JP2004009268A

JP2004009268A - Hard film coated high speed steel roughing end mill

Info

Publication number: JP2004009268A
Application number: JP2002169871A
Authority: JP
Inventors: Takashi Ishikawa; 石川　剛史
Original assignee: Hitachi Tool Engineering Ltd
Current assignee: Moldino Tool Engineering Ltd
Priority date: 2002-06-11
Filing date: 2002-06-11
Publication date: 2004-01-15

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hard film coated roughing end mill capable of attaining high speed and long life of rough cutting by a roughing end mill. <P>SOLUTION: In this hard film coated high speed steel roughing end mill, at least one or more layers of a hard film containing elements selected among one or more kinds selected among elements in 4a, 5a and 6a groups of a periodic table and Al and Si, elements selected among one or more kinds of at least N, C and O and a B element are coated. At least one layer of the hard film contains bond energy of B and N by an X-ray photoelectron spectroscopic analysis and is the hard film in which either one of bond energy of Ti and O or bond energy of Cr and O is recognized. V and Co included in a base material of the high speed steel is in the range of 3≤(V+Co)≤11 in wt.%. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明が属する技術分野】
本発明は、金型や機械構造部品に代表される金属材料等の切削加工において、主に粗削り用として用いられるエンドミル（以下、ラフィングエンドミルと呼ぶ。）に関する。
【０００２】
【従来の技術】
金型や機械構造部品に代表される金属材料等の粗加工用工具として、外周刃先部に連続して波状に形成された、波状切刃を有するラフィングエンドミルが使用されている。この波状切刃は、波状切刃のない直刃エンドミルと比べ切削加工時の切削応力が分散されるため、工具径に対する切込み量を大きくとることができ、荒削り加工に適する。このようにラフィングエンドミルは、通常の波状切刃を有しない直刃エンドミルによる切削加工よりも大きな衝撃力が刃先に加わると同時に、単位時間あたりの切屑排出量が多くなり、切屑が排出される波状切刃近傍の逃げ面側及びすくい面側は極めて高温にさらされる。そこで、ラフィングエンドミルの波状切刃近傍の工具摩耗を抑制するために、皮膜硬度がＨＶ（２００）０以上のＴｉＮ、ＴｉＣＮ等の硬質皮膜を被覆することも行なわれている。更に、例えば、特許第２５７６４００号に代表される従来のＴｉＮよりも皮膜硬度並びに耐酸化性の改善がなされたＴｉＡｌＮを被覆したラフィングエンドミル等も提案されている。しかしながら、更に近年の切削加工の分野では、粗切削加工の長寿命化並びにコスト低減のため、高能率化を目的とした高速加工及び被加工物の高硬度化等が求められており、これらＴｉＣＮ皮膜やＴｉＡｌＮ皮膜を被覆したラフィングエンドミルでは、これらの要求に対して満足される切削寿命は得られてはいない。
【０００３】
【発明が解決しようとする課題】
本発明者は、金属の粗加工におけるラフィングエンドミルの波状切刃近傍の逃げ面及びすくい面の損傷状態を注意深く解析した結果、工具逃げ面側では硬質皮膜内に酸素が拡散しており、皮膜最表面にＴｉとＯが結合した強度の低い酸化物を形成し、この強度の低い酸化物を起点とした硬質皮膜の脱落が繰り返されている事実を突き止めた。また、切屑の排出部となる工具すくい面側では被加工物である鉄と酸素が皮膜内部に拡散しており、この鉄と酸素が硬質皮膜の酸化を助長し摩耗が進行していた。以上のように、波状切刃先端近傍では著しく温度が上昇し、硬質皮膜の酸化と被加工物からの鉄の拡散並びに波状切刃逃げ面のアブレッシブ摩耗等が総合的に影響し、その結果工具切刃の欠損もしくはチッピングが発生し、切削工具の短寿命を招いていることが明らかとなった。従って、ラフィングエンドミルにおける切削加工の高能率化においては、波状切刃表面に被覆する硬質皮膜が高硬度で且つ高温環境下で優れた耐酸化性を有し、切削過程で被加工物から硬質皮膜内へ拡散する鉄に対して、親和性の低い硬質皮膜を被覆することにより、切削温度の上昇を抑制させる必要がある。また、工具母材としては、これら高硬度からなる硬質皮膜との密着性を維持するために靭性のある耐チッピング性に優れた母材とする必要がある。
【０００４】
本発明はこうした事情に鑑み、ラフィングエンドミルの波状切刃部表面に被覆する硬質皮膜は、高硬度であり且つ高温環境下で優れた耐酸化性を有することとし、また切削過程で被加工物から硬質皮膜内部に拡散する鉄に対して親和性の低い硬質皮膜を被覆することにより切削温度の上昇を抑制させる必要があると考えた。また同時に、極めて高硬度である硬質皮膜を被覆するため、ラフィングエンドミル母材と硬質皮膜との密着性を維持するために靭性のある耐チッピング性に優れかつ耐熱性に優れた母材とする必要があると考えた。これらの改善により、ラフィングエンドミルによる粗切削加工の高速化並びに長寿命化を達成することのできる硬質皮膜被覆ラフィングエンドミルの構成を提供することを課題とする。
【０００５】
【課題を解決するための手段】
これら課題を達成するための本発明は、周期律表の４ａ、５ａ、６ａ族の元素及びＡｌ、Ｓｉから選ばれる１種以上から選択された元素と、少なくともＮ、Ｃ、Ｏのうち１種以上より選択された元素とＢ元素を含む硬質皮膜を少なくとも１層以上被覆した硬質皮膜被覆高速度鋼製ラフィングエンドミルにおいて、該硬質皮膜の少なくとも１層は、Ｘ線光電子分光分析でＢとＮの結合エネルギーを含み、ＴｉとＯの結合エネルギーもしくはＣｒとＯの結合エネルギーのどちらかが認知される硬質皮膜であり、該高速度鋼の母材中に含まれるＶ及びＣｏが、重量％で３≦（Ｖ＋Ｃｏ）≦１１の範囲であることを特徴とする硬質皮膜被覆高速度鋼製ラフィングエンドミルである。
【０００６】
【発明の実施の形態】
ラフィングエンドミルによる粗切削加工の高速化並びに長寿命化を達成する為には、上述した通り、ラフィングエンドミルの波状切刃部表面に被覆する硬質皮膜は、高硬度であり、且つ、高温環境下で優れた耐酸化性を有すること、並びに切削過程で被加工物から硬質皮膜内部に拡散する鉄に対して親和性の低い硬質皮膜を被覆することにより、切削温度の上昇を抑制させる必要がある。また同時に、極めて高硬度である硬質皮膜を被覆するため、ラフィングエンドミル母材と硬質皮膜との密着性を維持するために靭性のある耐チッピング性に優れ、且つ、耐熱性に優れた母材とすることが重要である。その手段として、該高速度鋼の母材中に含まれるＶ及びＣｏが、重量％で３≦（Ｖ＋Ｃｏ）≦１１の範囲にすることが極めて有効である。上記該硬質皮膜は、皮膜硬度並びに高温環境下における耐酸化性に優れ、また被加工物中の鉄に対して、親和性が低く、潤滑作用を併せ持っているため、切削温度の上昇を抑制する作用を有する。これは該硬質皮膜内にＢＮとして存在することにより、高温環境下で該硬質皮膜最表面のＢＮ結合が、ＢとＯの結合に変わり、緻密で強度の高いＢ酸化物を硬質皮膜最表面に形成し、この緻密で強度の高いＢ酸化物がその後の酸化防止層として作用するためである。また同時に、緻密で強度の高いＢ酸化物は動的な酸化環境下においても、該硬質皮膜と剥離し難く酸化を抑制する。更に、硬質皮膜の高温環境下における軟化は、酸素の拡散に起因するため、耐酸化性に著しく優れる本発明皮膜は高温硬度に関しても著しく改善されるものである。更に、硬質皮膜内にＢＮとして存在する場合の利点として、鉄に対して極めて親和性が低いことである。このことにより、被加工物である鉄に対して優れた摩擦特性を示し、切削温度の上昇を抑制する。更に、硬質皮膜の高硬度化に対しても、硬質皮膜内にＢＮとして存在する場合、硬質皮膜格子内の内部応力を高め、硬質皮膜を著しく高硬度化させる。しかしながら、高硬度化されると同時に、硬質皮膜内に残留する圧縮応力も高くなってしまうため、硬質皮膜との密着性を維持するために靭性のある耐チッピング性に優れた母材とし、同時に耐熱性を付与することが必要である。そこで、母材中に含まれるＶ及びＣｏを、重量％で３≦（Ｖ＋Ｃｏ）≦１１の範囲に限定する必要がある。この範囲であれば、上記硬質皮膜内に発生する残留圧縮応力に対しても、母材内部で緩和することが可能であり密着性に優れ、上記該硬質皮膜の優れた耐酸化性と高硬度である特性を充分に発揮することができる。また、母材中のＶとＣｏが上記範囲を満足する場合、該硬質皮膜を被覆した場合の母材硬度と靭性のバランスが良く、また高速度鋼中のマトリックスの耐熱強度も優れる。これらの構成により、ラフィングエンドミルによる粗切削加工の高速化並びに長寿命化を達成することが可能となる。
【０００７】
硬質皮膜としては、該硬質皮膜内に最小結晶粒径が０．５ｎｍ以上、５０ｎｍ以下である結晶質相と、アモルファス相を含み、更に、該硬質皮膜はＸ線回折における回折強度が（２００）面で最大ピークを示し、その（２００）面の回折線が２θの半価幅で１．５度以上であることとする。更に好ましくは、該硬質皮膜の少なくとも１層が、Ｂ元素と金属成分としてＴｉもしくはＣｒ、及びＴｉとＣｒを主成分とする硬質皮膜であり、該硬質皮膜とは別の少なくとも１層は金属元素として少なくともＡｌとＴｉを含み、非金属元素として少なくともＮを含む硬質皮膜を用いることがより好ましい。
【０００８】
このような構成を採用することで、ラフィングエンドミルの波状切刃部表面に被覆する硬質皮膜は、高硬度であり且つ高温環境下で優れた耐酸化性を有し、並びに切削過程で被加工物から硬質皮膜内部に拡散する鉄に対して親和性の低い硬質皮膜となり、切削温度の上昇を抑制させることが可能となる。しかしながら、これら硬質皮膜の改善とともに、ラフィングエンドミル母材中の（Ｖ＋Ｃｏ）重量％含有量に関しても最適化を行う必要があり、極めて高硬度を有する硬質皮膜を被覆した場合にも、硬質皮膜内に発生する残留圧縮応力が母材内部で緩和され、高靭性であり耐チッピング性に優れ、また耐熱性をも併せ持った被覆ラフィングエンドミルが得られる。これらの改善により、ラフィングエンドミルによる粗切削加工の高速化並びに長寿命化が達成され、従来技術の課題を解決するに至った。
【０００９】
本発明である硬質皮膜を被覆したラフィングエンドミル母材として用いる高速度鋼は、上述したように、母材中に含まれるＶ及びＣｏが、重量％で３≦（Ｖ＋Ｃｏ）≦１１の範囲である必要がある。母材中のＶ及びＣｏは高速度鋼の硬度及び耐熱強度を決定する添加元素であると同時に靭性と耐摩耗性を決定する添加元素でもある。３重量％未満の場合は、高温環境下における母材強度が十分ではなく、工具寿命は不安定であった。これは、切削過程において波状切刃逃げ面側へ塑性変形を生じるためである。一方、１１重量％を越える場合は、該硬質皮膜内に発生する残留圧縮応力の緩和が不十分であり、密着性が十分ではなく、微細な皮膜剥離が発生する場合があり、波状切刃の山部にチッピングや欠けが発生してしまい短寿命を招いた。これらの結果より、本発明である該硬質皮膜と該ラフィングエンドミル母材への密着強度を考慮した結果、高速度鋼中のＶとＣｏの含有量を上記範囲内に決定した。また、該硬質皮膜中にＢとＮの結合が確認されない場合、上述したように皮膜硬度、耐酸化性並びに潤滑特性ともに十分ではなく、従来課題を解決するには至らなかった。また、ＢとＮの結合エネルギーは認められるが、ＴｉとＯの結合エネルギーとＣｒとＯの結合エネルギーの何れも認められない場合は、潤滑特性が十分ではなく、切削温度の上昇を抑制するには至らなかった。
【００１０】
本発明の高速度鋼は、母材硬さがＨＲＣ６４以上、ＨＲＣ６８未満であることが好ましい。母材硬度がＨＲＣ６４未満となる場合、過酷な切削環境下において波状切刃の山部が逃げ面側へ塑性変形を伴った摩耗進行も確認され、刃先強度が十分ではなく好ましくない。また、ＨＲＣ６８を超える場合は、該硬質皮膜内に発生する残留圧縮応力の緩和が不十分であり、微細な皮膜剥離が発生する場合が確認され、好ましくない。硬質皮膜は、該硬質皮膜内に最小結晶粒径が０．５ｎｍ以上、５０ｎｍ以下である結晶質相と、アモルファス相を含むことが望ましい。硬質皮膜内の最小結晶粒径が０．５ｎｍ以上、５０ｎｍ以下となる場合、皮膜硬度が高く、且つ高温硬度も著しく改善され、更に耐摩耗性に優れ好ましい。また、同時にアモルファス相を含む場合は、結晶と結晶の界面のような明瞭な結晶粒界がない為、結晶粒界を介して進行する酸素の拡散抑制に効果的であり、より好ましい。本硬質皮膜は、（２００）面に強く配向した場合が最も皮膜内の格子欠陥が少なく、高密度であり耐酸化性に優れることより（２００）面に最大のピーク強度をもつことが好ましい。更にその半価幅が１．５度以上の広がりを有する場合、皮膜硬度並びに耐酸化性改善への寄与が大きく好ましい。本硬質皮膜の少なくとも１層が、Ｂ元素と金属成分としてＴｉもしくはＣｒ、及びＴｉとＣｒを成分とする硬質皮膜であることが更に好ましい。Ｂ元素と、金属成分として、ＴｉもしくはＣｒ、及びＴｉとＣｒ、より構成される場合、皮膜硬度、耐酸化性並びに摺動特性のバランスに優れ、更に好ましい。
【００１１】
上記、該硬質皮膜は該ラフィングエンドミル被覆母材と優れた密着性、皮膜硬度及び耐酸化性を有すものの、母材との密着性を更に改善し、切削寿命を安定化させるために、他層と組み合わせることも可能であり、好ましい。この特性を満足できる硬質皮膜として、金属元素として少なくともＡｌとＴｉを含み、非金属元素として少なくともＮを含む硬質皮膜である。更に、硬質皮膜の母材への密着性を改善し、切削寿命を延ばすために、被覆前後に波状切刃近傍のバリやカエリ、及び被覆中に付着したドロップレット等の欠陥をショットブラスト等の機械的処理により除去することも好ましい。以下、本発明を実施例に基づいて説明するが、下記実施例は本発明を限定するものではなく、本発明主旨に基づき適宜変更を施すことは何れも本発明の技術的範囲に含まれるものである。
【００１２】
【実施例】
本発明の硬質皮膜被覆高速度鋼製ラフィングエンドミルは、その被覆方法については，特に限定されるものではないが，被覆母材への熱影響、工具の疲労強度、皮膜の密着性等を考慮した場合、比較的低温で被覆でき、被覆した皮膜に適度な圧縮応力が残留するアーク放電方式イオンプレーティング法による被覆処理を行なった。アークイオンプレーティング装置を用い、金属成分の蒸発源である各種合金製ターゲット、並びに反応ガスであるＮ_２ガス、ＣＨ_４ガス、Ａｒ＋Ｏ_２混合ガス、Ｂ_３Ｎ_３Ｈ_６ガスから目的の皮膜が得られるものを選択し，被覆母材温度４００℃，反応ガス圧力３．０Ｐａの条件下にて、被覆母材である各種高速度工具鋼製外径１２ｍｍの４刃ラフィングエンドミルにバイアス電圧−１５０Ｖを印加して、全皮膜の厚みが４μｍとなるように被覆処理を行った。硬質皮膜中へのＢ添加に関しては、金属ターゲット内に予め所定量添加した合金ターゲットを用いる場合と、被覆中にＢ含有気体を真空容器内に導入する場合においても可能である。更に必要に応じ予め、アークイオンプレーティング法によりＴｉＡｌＮ系皮膜を被覆した後、該硬質皮膜を被覆した。
【００１３】
【表１】

【００１４】
表１において、組成の定量分析にはエネルギー分散型Ｘ線分光法、オージェ光電子分光法及び電子線エネルギーロス分光法により総合的に決定した。また、Ｘ線光電子分光分析によるＢとＮの結合エネルギー、ＴｉとＯの結合エネルギー、ＣｒとＯの結合エネルギーの定性分析には、硬質皮膜表面を１０分間Ａｒイオンミーリング後ＳｉＯ_２換算で表面から約２０ｎｍ除去に行なった。分析結果を表１に併記する。該硬質皮膜内のアモルファス相の定性分析及び結晶質相からなる最小結晶粒径の測定は、硬質皮膜断面を透過型電子顕微鏡によりランダムに選択した視野の断面写真より行なった。表１に透過型電子顕微鏡による断面写真から実測した結晶質相からなる最小結晶粒径を併記する。結晶粒径の実測方法は、断面写真から断面の面積を円の面積として置き換えた場合の直径である等価円直径により求めた。
【００１５】
得られた本発明例を用い、次に示す切削条件にて、刃先の欠けないしは摩耗等により工具が切削不能となるまで加工を行い、その時の切削長を工具寿命とした。工具：４枚刃ラフィングエンドミル、外径１２ｍｍ
切削方法：側面切削ダウンカット
被削材：ＳＫＤ６１ＨＲＣ２０
切込み：Ａｄ１８ｍｍ×Ｒｄ１０ｍｍ
切削速度：７０ｍ／ｍｉｎ
送り：０．１ｍｍ／ｔｏｏｔｈ
切削油：エアーブロー
表１に本発例及び比較例の詳細及びその切削結果を示す。また、併せて同一切削条件で加工した従来例についても表２に示す。
【００１６】
【表２】

【００１７】
表１に示す本発明例は、従来例に比して安定した切削寿命が得られている。以下本発明例の詳細について述べる。表１に示す各組成の透過型電子顕微鏡による格子像観察結果から、本発明例の硬質皮膜内には何れも皮膜全体のＢ含有量よりもＢ含有量が多いアモルファス相が確認された。図１に本発明例１の硬質皮膜のＸ線光電子分光分析によるＴｉの２ｐ軌道から得られる結合エネルギーを示し、少なくともＴｉとＮ、ＴｉとＯの結合エネルギーが確認された。図２に本発明例１の硬質皮膜のＸ線光電子分光分析によるＢの１ｓ軌道から得られる結合エネルギーを示し、少なくともＢとＮの結合エネルギーが確認された。図３に本発明例６の硬質皮膜のＸ線光電子分光分析によるＣｒの２ｐ軌道から得られる結合エネルギーを示し、少なくともＣｒとＮ、ＣｒとＯの結合エネルギーが確認された。
本発明例１、２、３はそれぞれ母材の（Ｖ＋Ｃｏ）重量％の合計が異なる場合の本発明例であるが従来例に比べ、切削寿命が長い。一方比較例１５、１６に母材中の（Ｖ＋Ｃｏ）重量％の合計が２．５重量％の場合と１２．１重量％の場合の比較例を示す。母材中の（Ｖ＋Ｃｏ）重量％の合計が２．５重量％の場合、波状切刃の逃げ面側へ塑性変形を生じ、母材強度が十分ではなく、チッピングが多発した。母材中の（Ｖ＋Ｃｏ）重量％の合計が１２．１重量％の場合は、微小な硬質皮膜剥離が観察され、高硬度を有する該硬質皮膜との密着性が悪く、不安定な摩耗状態であり、本発明である該硬質皮膜の特性を十分に発揮できなかった。したがって、ラフィングエンドミルによる粗切削加工においては硬質皮膜により、被覆母材の影響がかなり大きいことが明らかである。本発明例４は母材の硬度がＨＲＣ６３．８であるが従来例に比べ切削寿命が長い。本発明例５は本発明である（ＴｉＳｉ）（ＮＯＢ）の場合であるが、従来例に比べ切削寿命が長い。本発明例６は本発明である該硬質皮膜の成分がＣｒである（ＣｒＳｉ）（ＣＮＯＢ）の場合であるが従来例に比べ切削寿命が長い。本発明例７は（ＣｒＴｉ）（ＮＯＢ）の場合であるが、従来例に比べ切削寿命が長い。本発明例８は本発明である該硬質皮膜単一層の場合であるが、従来例に比べ切削寿命が長いものの、（ＴｉＡｌ）Ｎ系皮膜等と組み合わせた多層膜がより好ましいといえる。本発明例９はＴｉ（ＣＮＯ）皮膜との多層膜であるが、従来例に比べ切削寿命が長い。本発明例１０は本発明である該硬質皮膜の最強強度を示す面指数が（１１１）面の場合であるが従来例に比べて切削寿命に優れるものの、（２００）面に最も強く配向する硬質皮膜がより好ましい。本発明例１１は（ＣｒＡｌＳｉ）（ＮＯＢ）皮膜との多層膜であるが従来例に比べ切削寿命が長い。本発明例１２は本発明である該硬質皮膜内の結晶質相の最小結晶粒径が５４ｎｍの場合であるが、従来例に比べて切削寿命に優れるものの、５０ｎｍ以下がより好ましいといえる。本発明例１３は該硬質皮膜のＸ線回折から得られる（２００）面の半価幅が１．５度未満の場合であるが従来例に比べて切削寿命が長いが１．５度以上がより好ましいといえる。本発明例１４は、被覆時にＢ気体を用いた場合の事例であり、該硬質皮膜はＴｉとＢのみからなる場合であるが従来例に比べ切削寿命が長い。
【００１８】
【発明の効果】
以上の如く、本発明の硬質皮膜被覆高速度鋼製ラフィングエンドミルは、従来の硬質皮膜被覆高速度鋼製ラフィングエンドミルに比べ、波状切刃表面に被覆する硬質皮膜が高硬度で且つ高温環境下で優れた耐酸化性を有し、切削過程で被加工物から硬質皮膜内へ拡散する鉄に対して、親和性の低い硬質皮膜であるため、切削温度の上昇を抑制させる効果を有する。またこれらの効果は、ラフィングエンドミル母材の最適な（Ｖ＋Ｃｏ）含有量に規定する必要があり、高靭性で耐チッピング性に優れた母材とし、高硬度硬質皮膜の残留圧縮応力を母材内部で緩和し、密着性に優れる。これらの改善により、波状切刃の山部のチッピング、欠けもしくは皮膜剥離等に起因した異常摩耗を著しく抑制することが可能となり、ラフィングエンドミルによる粗切削加工の高速化並びに長寿命化により、生産性向上並びにコスト低減に極めて有効である。
【図面の簡単な説明】
【図１】図１は、本発明例１のＸ線光電子分光分析によるＴｉの結合エネルギーを示す。
【図２】図２は、本発明例１のＸ線光電子分光分析によるＢの結合エネルギーを示す。
【図３】図３は、本発明例６のＸ線光電子分光分析によるＣｒの結合エネルギーを示す。[0001]
TECHNICAL FIELD OF THE INVENTION
TECHNICAL FIELD The present invention relates to an end mill (hereinafter, referred to as a roughing end mill) mainly used for rough cutting in cutting of a metal material or the like represented by a mold or a mechanical structural component.
[0002]
[Prior art]
A roughing end mill having a wavy cutting edge continuously formed in a wavy shape on an outer peripheral edge is used as a roughing tool for a metal material or the like represented by a mold or a mechanical structural component. This corrugated cutting edge disperses the cutting stress at the time of cutting compared to a straight-edged end mill having no corrugated cutting edge, so that the cutting amount with respect to the tool diameter can be increased, and is suitable for rough cutting. In this way, the roughing end mill applies a greater impact force to the cutting edge than cutting by a normal straight blade end mill that does not have a wavy cutting edge, and at the same time, the amount of chips discharged per unit time increases, and the wavy The flank side and rake side near the cutting edge are exposed to extremely high temperatures. Therefore, in order to suppress tool wear near the corrugated cutting edge of the roughing end mill, a hard coating such as TiN or TiCN having a coating hardness of HV (200) 0 or more is also used. Further, for example, a roughing end mill coated with TiAlN having improved film hardness and oxidation resistance over conventional TiN represented by Japanese Patent No. 2576400 has been proposed. However, in the field of cutting in recent years, in order to prolong the service life and reduce the cost of rough cutting, high-speed processing for the purpose of high efficiency and high hardness of the workpiece are required. With a roughing end mill coated with a coating or a TiAlN coating, a cutting life that satisfies these requirements has not been obtained.
[0003]
[Problems to be solved by the invention]
The present inventor carefully analyzed the damage state of the flank and rake face near the wavy cutting edge of the roughing end mill in the rough machining of metal.As a result, oxygen diffused into the hard coating on the tool flank side, It has been found out that a low-strength oxide in which Ti and O are bonded is formed on the surface, and the hard coating is repeatedly dropped off from the low-strength oxide. Also, on the tool rake face side, which is a chip discharge portion, iron and oxygen as workpieces diffused into the coating, and the iron and oxygen promoted oxidation of the hard coating and wear was progressing. As described above, the temperature rises remarkably near the tip of the wavy cutting edge, and the oxidation of the hard coating, the diffusion of iron from the workpiece, and the abrasive wear of the flank of the wavy cutting edge have an overall effect. It became clear that chipping or chipping of the cutting edge occurred, leading to a short life of the cutting tool. Therefore, in improving the efficiency of cutting in a roughing end mill, the hard coating covering the surface of the wavy cutting edge has high hardness and excellent oxidation resistance in a high-temperature environment. It is necessary to suppress an increase in the cutting temperature by coating a hard film having low affinity with respect to iron that diffuses into the inside. Further, as a tool base material, it is necessary to use a base material having toughness and excellent chipping resistance in order to maintain adhesion with the hard film having high hardness.
[0004]
In view of such circumstances, the present invention determines that the hard coating that coats the corrugated cutting edge surface of the roughing end mill has high hardness and excellent oxidation resistance in a high-temperature environment. We thought that it was necessary to suppress the rise in cutting temperature by coating a hard coating with low affinity for iron diffusing into the hard coating. At the same time, it is necessary to use a base material with excellent toughness and chipping resistance and heat resistance in order to maintain the adhesion between the roughing end mill base material and the hard film in order to coat a hard film with extremely high hardness. I thought there was. It is an object of the present invention to provide a hard coating-coated roughing end mill capable of achieving high-speed rough cutting by a roughing end mill and prolonging its life by these improvements.
[0005]
[Means for Solving the Problems]
In order to achieve these objects, the present invention provides an element selected from at least one element selected from the group consisting of elements of groups 4a, 5a, and 6a of the periodic table and Al and Si, and at least one element selected from the group consisting of N, C, and O. In a hard coating-coated high-speed steel roughing end mill coated with at least one hard coating containing an element selected from the above and the B element, at least one layer of the hard coating is formed of B and N by X-ray photoelectron spectroscopy. It is a hard coating that contains binding energy and recognizes either the binding energy of Ti and O or the binding energy of Cr and O. V and Co contained in the base material of the high-speed steel are 3% by weight. ≦ (V + Co) ≦ 11 is a rough coating end mill made of high-speed steel coated with a hard coating.
[0006]
BEST MODE FOR CARRYING OUT THE INVENTION
In order to achieve high speed and long life of rough cutting by roughing end mill, as described above, the hard coating covering the wavy cutting edge surface of roughing end mill has high hardness and under high temperature environment. It is necessary to suppress an increase in cutting temperature by having excellent oxidation resistance and coating a hard film having low affinity for iron that diffuses from the workpiece into the hard film during the cutting process. At the same time, to coat a hard coating that is extremely high in hardness, it has excellent toughness and chipping resistance to maintain the adhesion between the roughing end mill base material and the hard coating, and a base material that has excellent heat resistance. It is important to. As a means for achieving this, it is extremely effective that V and Co contained in the base material of the high-speed steel be in the range of 3 ≦ (V + Co) ≦ 11 by weight%. The hard coating has excellent coating hardness and oxidation resistance in a high-temperature environment, and has a low affinity for iron in a workpiece and has a lubricating effect, thereby suppressing an increase in cutting temperature. Has an action. This is because the presence of BN in the hard coating changes the BN bond on the outermost surface of the hard coating into a bond of B and O under a high temperature environment, and a dense and high-strength B oxide is applied to the outermost surface of the hard coating. This is because the dense and high-strength B oxide functions as a subsequent antioxidant layer. At the same time, the dense and high-strength B oxide is less likely to peel off from the hard coating even under a dynamic oxidizing environment and suppresses oxidation. Further, since the softening of the hard coating in a high-temperature environment is caused by diffusion of oxygen, the coating of the present invention, which is excellent in oxidation resistance, is also remarkably improved in high-temperature hardness. Another advantage of the presence of BN in the hard coating is that it has a very low affinity for iron. Thereby, it shows an excellent friction characteristic with respect to iron as a workpiece, and suppresses an increase in cutting temperature. Further, when BN is present in the hard coating, the internal stress in the hard coating lattice is increased, and the hardness of the hard coating is significantly increased. However, at the same time as the hardness is increased, the compressive stress remaining in the hard coating also increases, so that a base material with excellent toughness and chipping resistance to maintain adhesion with the hard coating, and at the same time, It is necessary to provide heat resistance. Therefore, it is necessary to limit V and Co contained in the base material to a range of 3 ≦ (V + Co) ≦ 11 by weight%. Within this range, even the residual compressive stress generated in the hard coating can be relaxed inside the base material, and has excellent adhesion, and the hard coating has excellent oxidation resistance and high hardness. Can be sufficiently exhibited. Further, when V and Co in the base material satisfy the above range, the base material hardness and toughness when coated with the hard coating are well-balanced, and the heat resistance of the matrix in the high-speed steel is also excellent. With these configurations, it is possible to achieve high speed and long life of rough cutting by the roughing end mill.
[0007]
The hard coating includes a crystalline phase having a minimum crystal grain size of 0.5 nm or more and 50 nm or less and an amorphous phase in the hard coating, and the hard coating has a diffraction intensity in X-ray diffraction of (200). A maximum peak is shown in the plane, and the diffraction line of the (200) plane is 1.5 degrees or more in a half width of 2θ. More preferably, at least one layer of the hard coating is a hard coating mainly containing element B and Ti or Cr as a metal component, and Ti and Cr as main components, and at least one layer other than the hard coating is a metal element. It is more preferable to use a hard coating containing at least Al and Ti as a material and at least N as a nonmetallic element.
[0008]
By adopting such a configuration, the hard coating covering the wavy cutting edge surface of the roughing end mill has high hardness and excellent oxidation resistance in a high temperature environment, and also has a work piece in a cutting process. The hard coating has low affinity for iron that diffuses into the hard coating from the inside, and it is possible to suppress an increase in cutting temperature. However, along with the improvement of these hard coatings, it is necessary to optimize the (V + Co) wt% content in the roughing end mill base material, and even when a hard coating having extremely high hardness is coated, The generated residual compressive stress is relaxed inside the base material, and a coated roughing end mill having high toughness, excellent chipping resistance, and heat resistance can be obtained. With these improvements, the rough cutting by the roughing end mill has been speeded up and the service life has been extended, and the problem of the prior art has been solved.
[0009]
As described above, in the high-speed steel used as a roughing end mill base material coated with a hard coating according to the present invention, V and Co contained in the base material are in a range of 3 ≦ (V + Co) ≦ 11 by weight%. There is a need. V and Co in the base metal are additive elements that determine the hardness and heat resistance of the high-speed steel, and are also additive elements that determine the toughness and wear resistance. When the amount is less than 3% by weight, the base material strength in a high-temperature environment was not sufficient, and the tool life was unstable. This is because plastic deformation occurs on the flank side of the wavy cutting edge in the cutting process. On the other hand, if it exceeds 11% by weight, the residual compressive stress generated in the hard coating is insufficiently relaxed, the adhesiveness is not sufficient, and fine coating peeling may occur, and the corrugated cutting edge Chipping and chipping occurred in the mountain, resulting in a short life. From these results, the content of V and Co in the high-speed steel was determined within the above range as a result of considering the adhesion strength between the hard coating and the roughing end mill base material according to the present invention. Further, when the bond between B and N is not confirmed in the hard coating, the coating hardness, oxidation resistance and lubricating properties are not sufficient as described above, and the conventional problems have not been solved. When the bond energy between B and N is recognized, but neither the bond energy between Ti and O or the bond energy between Cr and O is recognized, the lubricating properties are not sufficient, and the increase in the cutting temperature is suppressed. Did not reach.
[0010]
The high-speed steel of the present invention preferably has a base metal hardness of HRC64 or more and less than HRC68. When the base metal hardness is less than HRC64, the abrasion progression accompanied by plastic deformation of the ridges of the wavy cutting edge toward the flank side under severe cutting environment is also confirmed, and the cutting edge strength is not sufficient, which is not preferable. On the other hand, if it exceeds HRC68, the residual compressive stress generated in the hard coating is insufficiently relaxed, and it is confirmed that fine coating peeling may occur, which is not preferable. The hard coating desirably includes a crystalline phase having a minimum crystal grain size of 0.5 nm or more and 50 nm or less and an amorphous phase in the hard coating. When the minimum crystal grain size in the hard film is 0.5 nm or more and 50 nm or less, the film hardness is high, the high-temperature hardness is remarkably improved, and the wear resistance is further improved, which is preferable. In addition, when an amorphous phase is contained at the same time, since there is no clear crystal grain boundary such as an interface between crystals, it is effective for suppressing diffusion of oxygen proceeding through the crystal grain boundary, which is more preferable. This hard coating preferably has the maximum peak intensity on the (200) plane because it has the least lattice defects in the coating when it is strongly oriented on the (200) plane, has high density and is excellent in oxidation resistance. Furthermore, when the half width has a spread of 1.5 degrees or more, the contribution to the improvement of the film hardness and the oxidation resistance is large, which is preferable. It is further preferable that at least one layer of the present hard coating is a hard coating containing a B element and Ti or Cr as a metal component, and Ti and Cr as components. When composed of the B element and Ti or Cr as the metal component, and Ti and Cr, the balance between the film hardness, the oxidation resistance, and the sliding characteristics is excellent, which is more preferable.
[0011]
Although the hard coating has excellent adhesion to the roughing end mill-coated base material, coating hardness and oxidation resistance, the hard coating further improves the adhesion with the base material and stabilizes the cutting life. Combinations with layers are possible and preferred. A hard coating that satisfies these characteristics is a hard coating containing at least Al and Ti as metal elements and at least N as a nonmetal element. Furthermore, in order to improve the adhesion of the hard coating to the base material and extend the cutting life, defects such as burrs and burrs near the wavy cutting edge before and after coating, and defects such as droplets adhering during coating, such as shot blasting, are It is also preferable to remove by mechanical treatment. Hereinafter, the present invention will be described based on examples, but the following examples do not limit the present invention, and any appropriate modifications based on the gist of the present invention are included in the technical scope of the present invention. It is.
[0012]
【Example】
The roughing end mill made of a high-speed steel coated with a hard coating of the present invention is not particularly limited in its coating method, but takes into account the thermal effects on the coated base material, the fatigue strength of the tool, the adhesion of the coating, and the like. In this case, a coating treatment was performed by an arc discharge ion plating method in which coating could be performed at a relatively low temperature and an appropriate compressive stress remained in the coated film. Using an arc ion plating apparatus, a target film made of various alloy targets, which are evaporation sources of metal components, and N ₂ gas, CH ₄ gas, Ar + O ₂ mixed gas, and B ₃ N ₃ H ₆ gas, which are reaction gases, form target films. The obtained material was selected, and under the conditions of a coating base material temperature of 400 ° C. and a reaction gas pressure of 3.0 Pa, a bias voltage of −150 V was applied to a 4-flute roughing end mill having an outer diameter of 12 mm made of various high-speed tool steels as a coating base material. Was applied to perform a coating treatment so that the thickness of the entire coating became 4 μm. Regarding the addition of B to the hard coating, it is possible to use an alloy target to which a predetermined amount is added in advance in a metal target or to introduce a B-containing gas into a vacuum vessel during coating. Further, if necessary, a TiAlN-based film was previously coated by an arc ion plating method, and then the hard film was coated.
[0013]
[Table 1]

[0014]
In Table 1, the quantitative analysis of the composition was comprehensively determined by energy dispersive X-ray spectroscopy, Auger photoelectron spectroscopy, and electron beam energy loss spectroscopy. For the qualitative analysis of B and N bond energies, Ti and O bond energies, and Cr and O bond energies by X-ray photoelectron spectroscopy, the hard film surface was subjected to Ar ion milling for 10 minutes, followed by SiO ₂ conversion from the surface. About 20 nm was removed. The analysis results are also shown in Table 1. The qualitative analysis of the amorphous phase in the hard film and the measurement of the minimum crystal grain size composed of the crystalline phase were performed from a cross-sectional photograph of a field of view in which the cross section of the hard film was randomly selected by a transmission electron microscope. Table 1 also shows the minimum crystal grain size of the crystalline phase actually measured from a cross-sectional photograph taken by a transmission electron microscope. The actual measurement method of the crystal grain size was determined from the equivalent circular diameter which is the diameter when the area of the cross section was replaced by the area of the circle from the cross section photograph.
[0015]
Using the obtained example of the present invention, machining was performed under the following cutting conditions until the tool could not be cut due to chipping or wear of the cutting edge, and the cutting length at that time was defined as the tool life. Tool: 4-flute roughing end mill, outer diameter 12mm
Cutting method: Side cut down cut Work material: SKD61HRC20
Cut: Ad18mm × Rd10mm
Cutting speed: 70m / min
Feed: 0.1mm / tooth
Cutting oil: Air blow Table 1 shows details of the present invention and comparative examples and cutting results. Table 2 also shows a conventional example processed under the same cutting conditions.
[0016]
[Table 2]

[0017]
In the example of the present invention shown in Table 1, a stable cutting life was obtained as compared with the conventional example. Hereinafter, the details of the present invention will be described. From the results of observation of the lattice images of the respective compositions shown in Table 1 with a transmission electron microscope, an amorphous phase having a B content higher than the B content of the entire coating was confirmed in each of the hard coatings of the present invention. FIG. 1 shows the binding energy obtained from the 2p orbit of Ti by X-ray photoelectron spectroscopy analysis of the hard coating of Example 1 of the present invention, and at least the binding energy of Ti and N and Ti and O was confirmed. FIG. 2 shows the binding energy obtained from the 1s orbital of B by X-ray photoelectron spectroscopy of the hard coating of Example 1 of the present invention, and at least the binding energy between B and N was confirmed. FIG. 3 shows the binding energy obtained from the 2p orbital of Cr by X-ray photoelectron spectroscopy of the hard coating of Example 6 of the present invention, and at least the binding energy of Cr and N and Cr and O was confirmed.
Examples 1, 2, and 3 of the present invention are examples of the present invention in which the sum of (V + Co) wt% of the base materials is different, but the cutting life is longer than the conventional example. On the other hand, Comparative Examples 15 and 16 show Comparative Examples in which the sum of (V + Co) wt% in the base material is 2.5 wt% and 12.1 wt%. When the total of (V + Co)% by weight in the base material was 2.5% by weight, plastic deformation occurred on the flank side of the wavy cutting edge, the base material strength was not sufficient, and chipping occurred frequently. When the total of (V + Co)% by weight in the base material is 12.1% by weight, minute hard film peeling is observed, adhesion to the hard film having high hardness is poor, and unstable wear is caused. In some cases, the properties of the hard coating of the present invention could not be sufficiently exhibited. Therefore, it is clear that the influence of the coated base material is considerably large due to the hard coating in the rough cutting by the roughing end mill. In Example 4 of the present invention, the hardness of the base material was 63.8, but the cutting life was longer than that of the conventional example. Inventive Example 5 is the case of (TiSi) (NOB) of the present invention, but has a longer cutting life than the conventional example. Inventive Example 6 is a case where the component of the hard coating of the present invention is Cr (CrSi) (CNOB), but has a longer cutting life than the conventional example. Example 7 of the present invention is the case of (CrTi) (NOB), but has a longer cutting life than the conventional example. Example 8 of the present invention is a case of the single layer of the hard coating of the present invention. However, although the cutting life is longer than that of the conventional example, it can be said that a multilayer film combined with a (TiAl) N type coating or the like is more preferable. Inventive Example 9 is a multilayer film with a Ti (CNO) film, but has a longer cutting life than the conventional example. Inventive Example 10 is a case in which the surface index indicating the strongest strength of the hard coating of the present invention is the (111) plane. Although the cutting life is superior to that of the conventional example, the hard coating that is most strongly oriented on the (200) plane Coatings are more preferred. Inventive Example 11 is a multilayer film with a (CrAlSi) (NOB) film, but has a longer cutting life than the conventional example. Inventive Example 12 is a case where the minimum crystal grain size of the crystalline phase in the hard coating according to the present invention is 54 nm. Although the cutting life is superior to that of the conventional example, it can be said that 50 nm or less is more preferable. Invention Example 13 is a case where the half-value width of the (200) plane obtained from the X-ray diffraction of the hard coating is less than 1.5 degrees. The cutting life is longer than that of the conventional example, but the cutting life is 1.5 degrees or more. It can be said that it is more preferable. Example 14 of the present invention is a case in which B gas is used at the time of coating, and the hard coating consists of only Ti and B, but has a longer cutting life than the conventional example.
[0018]
【The invention's effect】
As described above, the hard coating-coated high-speed steel roughing end mill of the present invention has a hard coating that coats the corrugated cutting surface with a higher hardness and a higher temperature environment than the conventional hard coating-coated high-speed steel roughing end mill. The hard coating has excellent oxidation resistance and low affinity for iron that diffuses from the workpiece into the hard coating during the cutting process, and thus has an effect of suppressing an increase in cutting temperature. In addition, these effects need to be regulated to the optimum (V + Co) content of the roughing end mill base material. The base material has high toughness and excellent chipping resistance, and the residual compressive stress of the high hardness hard film is reduced in the base material. To relax and provide excellent adhesion. These improvements make it possible to significantly suppress abnormal wear caused by chipping, chipping, or peeling of the coating on the peaks of the wavy cutting edge. It is extremely effective for improvement and cost reduction.
[Brief description of the drawings]
FIG. 1 shows the binding energy of Ti by X-ray photoelectron spectroscopy of Example 1 of the present invention.
FIG. 2 shows the binding energy of B by X-ray photoelectron spectroscopy of Example 1 of the present invention.
FIG. 3 shows the binding energy of Cr by X-ray photoelectron spectroscopy of Example 6 of the present invention.

Claims

Including elements selected from the group 4a, 5a, and 6a of the periodic table and at least one element selected from Al and Si, and at least one element selected from at least one of N, C, and O and the B element In a hard coating-coated high-speed steel roughing end mill coated with at least one hard coating, at least one layer of the hard coating contains a binding energy of B and N by X-ray photoelectron spectroscopy, and a binding energy of Ti and O. Alternatively, it is a hard film in which either the binding energy of Cr and O is recognized, and V and Co contained in the base material of the high-speed steel are in a range of 3 ≦ (V + Co) ≦ 11 by weight%. A roughing end mill made of high-speed steel coated with a hard coating.

In the hard coating coated high speed steel roughing end mill according to claim 1, the particle diameter of crystal grains contained in the hard coating is defined as an equivalent circular diameter which is a diameter when the area of the particle cross section is replaced by the area of a circle. A hard film-coated high-speed steel roughing end mill comprising a crystalline phase having a minimum crystal grain size of 0.5 nm or more and 50 nm or less, and an amorphous phase.

3. The hard film-coated high-speed steel roughing end mill according to claim 1, wherein the hard film has a diffraction peak in X-ray diffraction at a (200) plane, and a diffraction line at the (200) plane. Is a roughing end mill made of a high-speed steel coated with a hard coating, having a half-width of 2θ of 1.5 ° or more.

The hard film-coated high-speed steel roughing end mill according to claim 1, wherein at least one layer of the hard film is a hard film containing a B element and a metal component of Ti or Cr, and a Ti and Cr component. A roughing end mill made of high-speed steel coated with a hard coating.

The rough coating end mill made of a high-speed steel coated with a hard coating according to any one of claims 1 to 4, wherein at least one layer other than the hard coating contains at least Al and Ti as metal elements and at least N as a nonmetal element. A roughing end mill made of high-speed steel coated with a hard coating.

The hard film coated high speed steel roughing end mill according to claim 1, wherein the high speed steel has a base material hardness of HRC64 or more and less than HRC68.