JP3606527B2

JP3606527B2 - Shaft cutting tool

Info

Publication number: JP3606527B2
Application number: JP28149193A
Authority: JP
Inventors: 勉吉田; 正弘町田; 勝石井; 稔福永
Original assignee: 三菱マテリアル神戸ツールズ株式会社
Priority date: 1993-11-10
Filing date: 1993-11-10
Publication date: 2005-01-05
Anticipated expiration: 2020-01-05
Also published as: JPH07138692A

Description

【０００１】
【産業上の利用分野】
本発明は、ドリル，エンドミルおよびリーマ等の軸物切削工具に関し、殊に軸物切削工具の刃部の耐摩耗性および耐ピッチング性を向上させる技術に関するものである。
【０００２】
【従来の技術】
粉末冶金法で製造されるＷＣ系超硬合金やＴｉＣ系サーメット等の硬質合金は、その優れた耐摩耗性を利用して旋削用チップ等として以前より広く利用されてきたが、これら材料の特性は、一般に高硬度になるほど脆くなる傾向にあると言われている。従って、これら硬質材料は切削・耐摩工具として一般に広く使用されている高速度工具鋼（以下、「ハイス」と略称する）に比べて靭性の面で難点を背負っていた。
【０００３】
しかしながら、近年に至り超微粒子超硬合金が発明されたことや粉末冶金法の難点であるポアーの発生を完全消滅できる熱間静水圧加圧処理（以下、「ＨＩＰ処理」と呼ぶ）が積極的に採用される等、製造法の進歩によってハイスに近い靭性を持つ硬質材料が開発されつつある。
【０００４】
一方、ドリルやエンドミル等の軸物切削工具の素材としては、ハイスが主に採用されているが、最近の高能率加工のニーズから日増しに高速加工の要求が高まっている。これらの軸物切削工具は、高速切削で広く使用されて理論面での解明が進んでいる旋削チップに比べ切削機構が複雑であり、切屑排出の問題と相俟って工具に加わる負荷も大きいので、折損，チッピング等の問題が容易に解決できず、これらの工具の高速切削への道が閉ざされていた。ところが、上述の如く超硬合金の関連技術が改良されるにつれて、軸物切削工具においてもＷＣ系超硬合金材料が普及する様になっており、その優れた硬さ、耐熱性、剛性を活かし、高速切削や高精度加工が一応可能になったと思われた。
【０００５】
しかしながら、使用条件によっては、突発的な折れ，欠けが発生することが指摘されている。この原因として、切削中に刃先先端に発生する切削熱による熱伝導性の悪さや摩耗劣化による切削抵抗の増加によるものと考えられる。従って、これら問題を解決しさらに信頼性を高めた超硬合金素材の開発が望まれているのが現状である。
【０００６】
【発明が解決しようとする課題】
例えばドリルによる切削は、旋削チップと異なって円周方向で切削条件が異なる複雑な機構を示す。即ち、基本的には軸中心に近づくほどスラストが増大する一方で、切削速度，トルクは急激に減少する傾向を示す。従って、軸中心のチゼル部では軸方向の押しつけ力が支配的に作用し、材質面からはこの力に抗する強度が要求される。一方外周部では切削速度が大となることから、耐熱性や耐摩耗性と耐チッピング性が要求される。しかしながら、現在使用されている超硬合金製ドリルのほとんどは、ＷＣを１．５〜２．５μｍの粗粒子をベースにして耐熱元素を添加した合金組成となっている。即ち、一般鋼材や鋳鉄などの穿孔加工に使用される超硬合金製ドリルは、穿孔加工中に発生する熱によってドリル寿命が大きく左右されると言われており、その対策として耐熱性を向上させる元素を多く添加した超硬合金を使用しているが、この様なドリル素材は耐熱元素の添加によって若干の熱伝導性が悪くなることから、一般的にＰ，Ｍ種といわれる超硬合金はＷＣを意識して粗粒化（１．５〜２．５μｍ程度）し、熱伝導性を向上させているのが現状である。
【０００７】
しかしながら、粗粒子のＷＣを用いると硬度が当然の如く低くなって耐摩耗性が低下し、刃先先端のマージン摩耗による切削性能の短寿命化につながることになる。またＷＣと結合相の不均一組織からくる耐チッピング性の面でも、従来使用されているドリルはまだ完全に解決されておらず、信頼性の面で問題点を残している。
【０００８】
ところでドリル等の軸物切削工具における欠けや折れの原因としては、材料面および形状面の双方からの影響があると思われる。そこで形状面でのドリルの具体例としては、ミラクルドリル（商品名：株式会社神戸製鋼所製）、ニューポイントドリル（商品名：三菱マテリアル株式会社製）、マルチドリル（商品名：住友金属株式会社製）、更には細井ドリル（商品名）の様に、チゼル部等の形状を工夫することによって欠けの問題を解消しようとした各種ドリルが商品化されている。またエンドミルにおいても、すくい角をポジにした刃先にして刃部にかかる負荷を減少したものや、加工仕上げ面を良くするために切れ刃をピン角にした工具等も提案されている。しかしながら、刃先部の局部摩耗やチッピング等により欠けや折れなどの折損による切削寿命のバラツキは完全には解消していないのが現状である。
【０００９】
一方、材料面から機能的特徴を生かした工具の開発も行なわれており、欠けや折れ等を防止するためには、一般的に抗折力を上げて靭性を向上することが有効な手段であると言われている。しかしながら、摩耗性と靭性とは相反する性質であり、靭性の優れた超微粒子合金においても例外ではない。その対策として、刃先に耐摩耗性の良い硬質物をコーティング（膜質はＴｉＣが主体）したドリルやエンドミル等が実用化・市販されているが、スローアウエイチップに比べ刃先形状が複雑なことから、コーティングが剥離しやすいという問題もある。また超微粒子合金を使用している超硬合金製エンドミルにおいても、より長い寿命を達成すべくコーティングを施した工具が出現しているが、寿命のバラツキや精度上で依然として問題がある。尚コーティング膜は、耐摩耗性と耐熱性に主眼をおいたものであり、欠けや折れの問題とは基本的には無縁である。
【００１０】
このような技術背景において、摩耗性と靭性を同時に改善しさらに切削性を向上する手段として、工具の複合化も有効である（例えば、特開平２−２６９５１５号）。この様な技術においては、複合化はろう付けによって達成されているのが一般的であり、例えば先ムクドリルなどの軸物切削工具では刃部が超硬合金製チップ、シャンク部が鋼材とする接合体となっているが、接合強度の不安やろう付け時の熱応力による接合部の折損剥離の問題を内在しており、工具使用の際の突発的折れ問題はまだ解決しないまま今日に至っている。また真空ろう付け技術も採用されてきているが、上述した熱応力や接合強度の問題は依然として残されている。
【００１１】
本発明はこうした状況の下になされたものであって、その目的は、耐摩耗性や耐チッピング性の向上を図ると共に、折損などの発生を防止し、性能を高めた軸物切削工具を提供することにある。
【００１２】
【課題を解決するための手段】
上記目的を達成し得た本発明の軸物切削工具とは、刃部が、ＷＣを主体とする超硬合金であって、Ｗを除く周期律表４Ａ，５Ａ，６Ａ族元素よりなる群から選ばれる１種以上の金属元素の炭化物粉末が０．２〜３０重量％であると共に、結合相となるＣｏおよび／またはＮｉの粉末が４〜２０重量％の割合で配合され、残部が平均粒径：０．３〜０．７μｍのＷＣ粉と不可避不純物である原料混合粉末を焼結した超硬合金となっている。
【００１３】
そして本発明の軸物切削工具とは、上記の様な超硬合金を刃部の素材として用いると共に、シャンク部として、Ｗを除く周期律表４Ａ，５Ａ，６Ａ族元素よりなる群から選ばれる１種以上の金属元素の炭化物粉末が０．１〜５重量％、結合相としてのＣｏおよび／またはＮｉの粉末が４〜８重量％の割合で配合され、残部が平均粒径：１〜３μｍのＷＣ粉と不可避不純物である原料混合粉末を焼結したものを用いる点に要旨を有するものである。
【００１４】
【作用】
本発明は、基本的には軸物切削工具の刃部となる超硬合金の出発原料混合粉末の構成を規定したものであるが、この原料混合粉末のうち、Ｗを除く周期律表４Ａ，５Ａ，６Ａ族元素よりなる群から選ばれる１種以上の金属元素の炭化物（以下、「耐熱性化合物」と呼ぶことがある）粉末の配合量は０．２〜３０重量％とする必要がある。即ち、この配合量が０．２重量％未満であると、これら化合物を配合する基本的作用である耐熱性向上が発揮されず、一方３０重量％を超えると急激な靱性低下を生じる。尚上記耐熱性化合物は、周期律表４Ａ，５Ａ，６Ａ族元素のうちＷを除く金属元素を基本的に想定したものであり、それにはいわゆるダブルカーバイドと呼ばれるＴｉＣ−ＴａＣ系炭化物粉末も含む趣旨であるが、必要によってその一部をＴｉＣ−ＴａＣ−ＷＣ（いわゆるトリプルカーバイド）の様にＷを含む炭化物粉末で代替しても良い。この様な粉末に含まれるＷＣは、超硬合金の主体となって硬質相をなすＷＣと異なり、耐熱性化合物として作用する。
【００１５】
上記耐熱性化合物粉末の平均粒径は、０．５〜１．０μｍであることが好ましく、この様な微細な粒子を用いることによって超硬合金の耐摩耗性を更に向上することができる。また耐熱性化合物のうち、ＴｉＣやＴａＣなどの化合物も粒成長抑制剤として効果はあるが、それ以上にＶＣは０．２〜０．５重量％程度のわずかな添加量でも粒成長抑制剤としての効果を発揮する。即ち、ＶＣの添加量が０．２重量％未満ではその効果は少なく、０．５重量％を超えると靭性の面で悪くなる傾向を示す。
【００１６】
一方、結合相となるＣｏおよび／またはＮｉの粉末混合量は４〜２０重量％とする必要があるが、これは４重量％未満では靭性の面で悪くなる傾向にあり、２０重量％を超えると摩耗性の面で劣る傾向にある。
【００１７】
本発明で用いる原料混合粉末は、上記の他、残部がＷＣ粉および不可避不純物からなるものであるが、ＷＣ粉の平均粒径は０．３〜０．７μｍ範囲の超微粒子を使用する必要がある。即ち、ＷＣ粉の平均粒径が０．７μｍ超えると硬さでＨ_ＲＡ：９１．８以上の値が得られず耐摩耗性の点で劣り、局部摩耗による寿命低下が生じることになり、本発明の目的が達成されない。
【００１８】
尚平均粒径０．３〜０．７μｍのＷＣ粉と、耐熱性化合物粉末の平均粒子径の差を０．１〜０．５μｍ以内に抑えた均一組織にすることで、耐摩耗性，耐チッピング性が更に優れたものとなる。
【００１９】
上記原料粉末を調製するときの配合・混合処理法は、従来の粉末冶金法で行なわれる通常の混合法を採用すれば良く、例えばアトライターにて適量な有機溶剤（アセトン、エタノール、ヘキサン等）と配合粉および成形助剤を添加して撹拌を行ない、スラリー状になった原料混合粉末を乾燥・造粒処理する。尚本発明で用いる原料混合粉末には、必要に応じてＨｆ，Ｚｒ，Ｂ等の元素の炭・窒化物を０．１〜５重量％の割合で混合しても良く、これらは耐酸化性，耐熱性に寄与する。
【００２０】
刃部の超硬合金は、上記の様な原料混合粉末を焼結することによって得られるが、その手順・手段については特に限定されず、例えば下記の方法に従えばよい。その一つとしては、金型若しくはゴム型に充填したのち、加圧または静水圧圧力で加圧し成形体を作る方法と、もう一つは乾燥された混合粉に成形助剤やバインダー（熱可塑性樹脂，潤滑剤等）を投入し、粘土状にした後、射出成形機にて押出し成形体を作る方法であり、本発明材はどちらの成形法にも適用される。また成形後は上記成形助剤やバインダーを取り除き、適当な強度を持たせる為に、半焼結処理（７００〜１０００℃）を施し、そのまま焼結処理（１２５０〜１５００℃）したり、加工を加えて所定の形状に仕上げて前記と同じ様に焼結処理をする。この際の焼結は、上記温度範囲で真空中（１×１０〜１×１０^５Ｔｏｒｒ）で処理する。焼結処理したものは不活性ガス（Ａｒ，Ｎ_２等）を圧力媒体として１２００〜１４００℃の温度で１００〜２０００ｋｇ／ｃｍｍ^２の圧力でＨＩＰ処理を施すのが好ましい。
【００２１】
焼結・ＨＩＰ処理後の組織は、ＷＣ，耐熱性化合物（ＴｉＣ，ＴａＣ，Ｃｒ_３Ｃ_２等）とも微細で均一な組織を呈することが本発明では重要である。即ち、粗粒を使用すると、図２に示す様な組織となり、結合相にＣｏリッチな相が形成され、局部摩耗の発生によるチッピングによる損傷や硬度低下による耐摩耗性劣化，熱伝導度の低下等が生じ易くなる。
【００２２】
従って、従来使用される粗粒系のＰ，Ｍ種素材では上記の様な損傷現象が起き易いのに比べ、本発明材は出発原料から微粒子を使用した原料混合粉末を用い、且つ粒成長しない処理方法で製造するため、図１に示す様な均一な組織となり、そのことより優れた耐摩耗性および耐チッピング性を有する超硬ドリル素材（刃部の素材）を製造することができる。
【００２３】
上記の様な超硬合金を刃部の素材とし、組成の異なる超硬合金をシャンク部として用い、これらを接合することによって軸物切削工具を構成することが本発明の技術的範囲に含まれるものであるが、シャンク部で用いる超硬合金の構成は下記の通りである。
【００２４】
シャンク部に用いる素材は、刃部で発生する切削熱を吸収し易い組成にすることが重要であり、その為熱伝導性の良好な組成を採用することで切削寿命を伸ばすようにする。熱伝導度の向上には、低Ｃｏ化を図り、ＷＣなどの炭化物粒子を粗粒にするのが良い。こうした観点から、ＷＣ粉末は平均粒径が１〜３μｍの粗粒のものを用い、且つ結合相となるＣｏおよび／またはＮｉを３重量％未満では靭性の点で不足し、また９重量％を超えると熱伝導性の面で劣るので、４〜８％の範囲の組成が最も有効である。
【００２５】
軸物切削工具において、刃部とシャンク部は前記の様な組成で構成され、その長さ比率は刃部：シャンク部＝２〜３×ｄ（外周径）：全長−（２〜３×ｄ（外周径））が最適である。これは被削材の板厚から考えて、切削性能に直接影響しない長さを選んだものである。すなわち刃部が２ｄ未満の長さでは接合界面がワークに直接接触する領域となり、境界摩耗などの損傷が生じることになり、また３ｄを超える長さでは刃部で発生する切削熱を伝導する機能が発揮できないことになり、従ってその接合体の刃先とシャンク部の比率範囲を上記の様に規定した。
【００２６】
刃部とシャンク部の接合界面は平面状ではなく、相互に嵌合する複数の凹溝および凸条とするのが効果的であり、そのピッチ間隔は０．１〜０．３ｍｍであるのが最も好ましい。このピッチが０．１ｍｍ未満では熱伝導性の面での効果が薄く、０．３ｍｍを超えると接合強度が低下する。即ち、本発明では、刃部に発生する切削熱をシャンク部側へ逃しやすいようにして、その機能が発揮できるようにピッチ間隔を規定したのである。尚前記複数の凹溝および凸条の具体的な形状については特に限定するものではなく、凹溝および凸条が延びる方向に対して垂直な面での形状が波状，鋸歯状等、いずれも含む趣旨である。
【００２７】
以上述べた様に、刃部に超微粒子の合金組成材を採用することにより、耐摩耗性および耐チッピング性に優れた性能を発揮すると共に、刃部で発生した切削熱をシャンク部側で吸収し易い、即ち熱伝導性の良い超硬合金素材からなるシャンク部に伝達することによって切削性能を更に向上させることができる。
【００２８】
以下本発明を実施例によって更に詳細に説明するが、下記実施例は本発明を限定する性質のものではなく、前・後記の趣旨に徴して設計変更することはいずれも本発明の技術的範囲に含まれるものである。
【００２９】
【実施例】
参考例１
平均粒径が０．５μｍのＷＣ粉末、平均粒径が１．５μｍのＣｏ粉末および／またはＮｉ粉末、ＴｉＣ，ＴａＣ，ＶＣ，Ｃｒ_３Ｃ_２，ＮｂＣ等のＷを除く周期律表４Ａ，５Ａ，６Ａ族金属の炭化物（耐熱性化合物）、あるいはトリプルカーバイド（ＴｉＣ−ＴａＣ−ＷＣ）やダブルカーバイド（ＴｉＣ−ＴａＣ）の粉末で平均粒径が０．７μｍのもの、または振動ミルやアトライターによって粉砕した粒径が１．０μｍ以下で平均粒径が０．８μｍの耐熱性化合物粉末等の出発原料を用いて表１および表２に示す配合組成を作った。
【００３０】
これら配合粉末をそれぞれアトライターに投入し、有機溶剤（アセトンかヘキサン）と成形助剤を同時に撹拌し、５時間後に回収し、乾燥・造粒処理を行なった。その後、所定の金型にて１０００ｋｇ／ｃｍ^２以上の圧力で成形体を成形し、半焼結処理（４５０℃×４時間＋８５０℃×２時間）を施した。その後ドリル形状に加工し、１×１０^４Ｔｏｒｒの真空中で１３８０℃×０．５時間の焼結処理を施したものを、さらに１３５０℃で１５００気圧の不活性ガス（Ａｒ）中でＨＩＰ処理した。焼結およびＨＩＰ処理後の素材特性（硬さ，抗折力）を表１および表２に併記する。
【００３１】
【表１】

【００３２】
【表２】

【００３３】
得られた超硬合金の切削性能の評価を行なうために、直径：１０ｍｍの超硬合金製ドリルに加工し、下記の条件にて穿孔加工を行なった。
被削材：Ｓ５０Ｃ
切削速度：１２０ｍｍ／ｍｉｎ
送り：０．２５ｍｍ／ｒｅｖ
切削油：エマルジョン
ドリル直径：１０．０ｍｍ
板厚：１．６×Ｄ（ドリル直径）
切削寿命は、切粉の形状変化と切削音の発生および刃先の異常摩耗から最終寿命を判断した。その結果、表３に示すように、参考材は従来材の約２〜３倍の寿命が得られ、また図３および図４に示すように、ＷＣ粒径と切削寿命との関係、硬度と切削寿命とが明確に関係付けられることが明らかにされた。
【００３４】
【表３】

【００３５】
実施例１
表４は、刃部とシャンク部で構成される本発明の軸物切削工具を製造する際の原料混合粉末の組成および特性を示す。また表５には従来使用されている原料混合粉末の組成と特性を示す。刃部の組成は超微粒子の粉末を出発原料として、ＷＣは０．５μｍをベースに、Ｗを除く周期律表の４Ａ，５Ａ，６Ａ族の粒子径が１．０μｍ以下の炭化物を０．２〜３０重量％添加し、結合相となるＣｏおよび／またはＮｉは４〜２０重量％の範囲となっている。また粒成長を抑える元素として、ＶＣも添加しており、以上のことにより耐摩耗性と関係が深い硬度の値が従来材に比べ、高い値を示しているのが分かる。一方シャンク部に適用される組成はＷＣの粒径が１〜３μｍの粗粒を使用し、Ｗを除く周期律表４Ａ，５Ａ，６Ａ族の炭化物を０．１〜５重量％添加し、もしくは無添加で、結合相となるＣｏおよび／またはＮｉは４〜８重量％の範囲としているものである。このことより熱伝導性も良く、本発明のねらいである刃部の発生した切削熱をシャンク側へ伝えやすくなっている。
【００３６】
【表４】

【００３７】
【表５】

【００３８】
表４および５に示した原料粉末を秤量，配合し、有機溶剤中アトライターにて混合・分散後、乾燥・造粒を行なった。そして得られた造粒粉は成形を行なう際、まずホッパーに蓄積された刃部に用いる造粒粉を所定の成形金型に投入、その後所定量のシャンク部で用いる造粒粉を振動を与えながら投入し、１０００ｋｇ／ｃｍ^２以上の圧力で成形処理を行なった。この場合刃先部の長さは２〜３×ｄ（外周径）寸法に、すなわち刃先：シャンク＝（２〜３×ｄ（外周径））：全長−（２〜３×ｄ（外周径））になるように造粒粉を夫々個別に投入し、目的とする成形体を製作した。この成形体を脱ろう・半焼したのち、半焼加工にて目的の素材形状に仕上げ、真空炉にて１×１０〜１×１０^−５Ｔｏｒｒの真空下、１２８０〜１５００℃の温度で焼結処理を行なった。その後Ａｒ等の不活性ガスを圧力媒体として１００〜２０００ｋｇ／ｃｍ^２の圧力で１２００〜１４００℃高温処理を行なう熱間静水圧加圧処理（ＨＩＰ処理）を施し、本発明合金の素材を得た。
【００３９】
本発明材および比較材を用い、切削テストを行なった。尚切削テストはドリル（１０ｍｍφ）とエンドミル（直径：１０ｍｍ，２枚刃）を用い、夫々下記の条件で行なった。また同一条件で比較するために、本発明材，比較材とも同一コーティング（Ａｌ，Ｔｉ）Ｎ処理したもので切削評価した。
（ドリルの切削条件）
切削速度：１２０ｍｍ／ｍｉｎ
送り：０．２５ｍｍ／ｒｅｖ
板厚：１６ｍｍ
被削材：Ｓ５０Ｃ，５０Ｃ
切削油：エマルジョン油
（エンドミルの切削条件）
回転数：１９１０ｒｐｍ
被削材：ＳＫＤ１１
送り：３０６ｍｍ／ｍ（０．０８ｍｍ／刃）
切込み：１．０ｍｍ（Ｒ）×１５ｍｍ（Ｌ）
切削方法：ダウンカット，エアーブロー
切削長：６ｍ
【００４０】
その結果を一括して表６に示すが、ドリルによる切削試験においては、本発明材は２０００穴以上の高寿命を示しているが、従来使用されている粗粒系ドリルでは、３００〜４００穴の寿命しか得られていない。これは同一被膜コーティング下でも超硬母材の摩耗性は切削性能に影響しており、本発明材は刃部の耐摩耗性の優れた組成で、且つシャンク部が刃部に発生する切削熱を軽減化する方向に作用したことによる効果と思われる。またエンドミルにおいても、減径摩耗量で本発明材は比較材の１／２の値となっており、上記と同様の効果によって優れた切削性能を発揮していることが分かる。
【００４１】
【表６】

【００４２】
表７は本発明材（Ｎｏ．２５）の抗折強度を調べた結果を示したものである。尚比較材として、エンドミル素材（刃部：４Ａ）の焼結体同士を接合したもの（図５（ｂ））の抗折強度についても調査した結果についても示す。またＡ部（接合強度）およびＢ部は、図５（ａ）に示す位置で測定した値である。本発明材における接合界面はポアーやクラック等の欠陥は全く認められず、刃部母材あるいはシャンク部母材とほぼ同じ値が得られており、このことは接合による強度低下はないということを証明していた。
【００４３】
【表７】

【００４４】
【発明の効果】
本発明は以上の様に構成されており、従来のものより穿孔加工等の寿命が高寿命化された軸物切削工具が実現できた。
【図面の簡単な説明】
【図１】本発明の超硬合金の組織を模式的に示す説明図である。
【図２】従来の超硬合金の組織を模式的に示す説明図である。
【図３】各超硬合金の硬度と切削寿命の関係を示すグラフである。
【図４】各超硬合金のＷＣ粉平均粒径と切削寿命の関係を示すグラフである。
【図５】抗折試験片を示す説明図である。[0001]
[Industrial application fields]
The present invention is a drill relates again and again axis thereof cutting Engineering such end mills and reamers, a technique which particularly enhance the shaft thereof blade section abrasion resistance and pitting resistance of the cutting tool.
[0002]
[Prior art]
Hard alloys such as WC-based cemented carbide and TiC-based cermet manufactured by powder metallurgy have been widely used as turning tips, etc., due to their excellent wear resistance. Is generally said to tend to become brittle as the hardness increases. Therefore, these hard materials suffer from a toughness as compared with high-speed tool steel (hereinafter, abbreviated as “HIS”) which is generally widely used as a cutting / abrasion resistant tool.
[0003]
However, in recent years, ultra-fine particle cemented carbide has been invented, and hot isostatic pressing (hereinafter referred to as “HIP treatment”) that can completely eliminate the generation of pores, which is a drawback of powder metallurgy, has been aggressive. As a result of advances in manufacturing methods, hard materials with toughness close to high speed are being developed.
[0004]
On the other hand, HSS is mainly used as a material for shaft cutting tools such as drills and end mills, but the demand for high-speed machining is increasing day by day due to recent needs for high-efficiency machining. These shaft cutting tools have a complicated cutting mechanism compared to the turning tips that are widely used in high-speed cutting and have been elucidated in theory, and the load applied to the tools is large due to the problem of chip discharge. Problems such as breakage and chipping could not be easily solved, and the road to high-speed cutting of these tools was closed. However, as related art of cemented carbide is improved as described above, WC-based cemented carbide materials are becoming popular in shaft cutting tools, taking advantage of their excellent hardness, heat resistance, and rigidity. It seemed that high-speed cutting and high-precision machining were possible.
[0005]
However, it has been pointed out that sudden breakage or chipping may occur depending on use conditions. This is thought to be due to poor thermal conductivity due to cutting heat generated at the tip of the blade during cutting or increased cutting resistance due to wear deterioration. Therefore, the present situation is that it is desired to develop a cemented carbide material that solves these problems and further enhances reliability.
[0006]
[Problems to be solved by the invention]
For example, cutting by a drill shows a complicated mechanism in which cutting conditions differ in the circumferential direction unlike a turning tip. In other words, the thrust increases as the shaft center is approached, while the cutting speed and torque tend to decrease rapidly. Therefore, the axial pressing force is dominant in the chisel portion at the center of the shaft, and the material surface is required to have strength against this force. On the other hand, since the cutting speed is increased at the outer peripheral portion, heat resistance, wear resistance and chipping resistance are required. However, most of the drills made of cemented carbide used at present have an alloy composition in which refractory elements are added based on coarse particles of WC of 1.5 to 2.5 μm. In other words, cemented carbide drills used for drilling of general steel materials and cast iron are said to have a great influence on the drill life due to the heat generated during drilling. Cemented carbide with a lot of elements added is used, but since such a drill material has some thermal conductivity worsened by the addition of heat-resistant elements, the cemented carbide generally called P and M types are At present, the WC is coarsened (about 1.5 to 2.5 μm) to improve the thermal conductivity.
[0007]
However, when coarse grain WC is used, the hardness is naturally lowered and the wear resistance is lowered, leading to a shortened cutting performance due to margin wear at the edge of the cutting edge. Also, in terms of chipping resistance resulting from a heterogeneous structure of WC and the binder phase, the conventionally used drill has not been completely solved yet, and there remains a problem in terms of reliability.
[0008]
By the way, it is considered that the cause of chipping or breaking in a shaft cutting tool such as a drill is influenced by both the material surface and the shape surface. Therefore, specific examples of drills in terms of shape include miracle drill (trade name: manufactured by Kobe Steel), new point drill (trade name: manufactured by Mitsubishi Materials Corporation), multi-drill (trade name: Sumitomo Metal Co., Ltd.) And various drills that attempt to solve the problem of chipping by devising the shape of the chisel portion etc., such as Hosoi drill (trade name). Also for end mills, there have been proposed a tool with a rake angle having a positive rake angle and a reduced load on the blade part, and a tool with a cutting edge having a pin angle to improve the finished surface. However, the present situation is that the variation in cutting life due to breakage such as chipping or breakage due to local wear or chipping of the cutting edge portion has not been completely eliminated.
[0009]
On the other hand, tools that make use of functional characteristics from the material side are also being developed, and in order to prevent chipping and breakage, it is generally an effective means to improve toughness by increasing the bending strength. It is said that there is. However, wear and toughness are contradictory properties, and ultrafine particle alloys with excellent toughness are no exception. As countermeasures, drills and end mills, etc. with a hard-coated hard tip (film quality mainly made of TiC) are put into practical use and marketed, but the shape of the cutting edge is more complex than the throwaway tip. There is also a problem that the coating is easily peeled off. In addition, even in cemented carbide end mills using ultrafine particle alloys, tools with coatings appearing to achieve a longer life have appeared, but there are still problems in terms of variation in life and accuracy. The coating film focuses on wear resistance and heat resistance, and is basically free from problems of chipping and breaking.
[0010]
In such a technical background, as a means for simultaneously improving wearability and toughness and further improving machinability, it is also effective to combine tools (for example, JP-A-2-269515). In such a technique, the compounding is generally achieved by brazing. For example, in a shaft cutting tool such as a tip drill, a joined body in which the blade portion is a cemented carbide tip and the shank portion is a steel material. However, there are inherent problems such as anxiety of joint strength and problems of fracture peeling of the joint due to thermal stress at the time of brazing, and sudden breakage problems at the time of tool use have yet to be solved. Moreover, although the vacuum brazing technique has been adopted, the above-described problems of thermal stress and bonding strength still remain.
[0011]
The present invention has been made under such circumstances, and an object of the present invention is to provide a shaft cutting tool having improved performance while preventing breakage and the like while improving wear resistance and chipping resistance. There is.
[0012]
[Means for Solving the Problems]
The shaft was cut engineering tools of the present invention were able to achieve the above objects, the blade portion, a cemented carbide mainly composed of WC, Periodic Table 4A except W, 5A, from the group consisting of Group 6A elements The carbide powder of one or more metal elements selected is 0.2 to 30% by weight, the powder of Co and / or Ni serving as a binder phase is blended at a ratio of 4 to 20% by weight, and the balance is the average grain Diameter: A cemented carbide obtained by sintering a WC powder of 0.3 to 0.7 μm and a raw material mixed powder which is an inevitable impurity .
[0013]
And the axial material cutting tool of the present invention, the use of the above such cemented carbide as a material of the blade, as a shank portion, the periodic table 4A except W, 5A, selected from the group consisting of Group 6A elements 1 The carbide powder of the metal element of the seeds or more is blended at a ratio of 0.1 to 5% by weight, the powder of Co and / or Ni as the binder phase is 4 to 8% by weight, and the balance is the average particle size: 1 to 3 μm It has a gist in that it uses sintered WC powder and raw material mixed powder which is an inevitable impurity.
[0014]
[Action]
The present invention basically defines the configuration of the starting raw material mixed powder of cemented carbide that becomes the blade part of the shaft cutting tool. Of these raw material mixed powders, periodic tables 4A and 5A excluding W are included. The amount of powder of carbide of one or more metal elements selected from the group consisting of Group 6A elements (hereinafter sometimes referred to as “heat-resistant compounds”) needs to be 0.2-30 wt%. That is, when the blending amount is less than 0.2% by weight, the improvement of heat resistance, which is a basic action of blending these compounds, is not exhibited. On the other hand, when the blending amount exceeds 30% by weight, a rapid decrease in toughness occurs. The heat-resistant compound is basically assumed to be a metal element other than W among the periodic table 4A, 5A, and 6A group elements, and includes a TiC-TaC-based carbide powder called double carbide. However, if necessary, a part thereof may be replaced with a carbide powder containing W like TiC-TaC-WC (so-called triple carbide). WC contained in such a powder acts as a heat-resistant compound, unlike WC, which is mainly composed of cemented carbide and forms a hard phase.
[0015]
The average particle diameter of the heat-resistant compound powder is preferably 0.5 to 1.0 μm, and the wear resistance of the cemented carbide can be further improved by using such fine particles. Of the heat-resistant compounds, compounds such as TiC and TaC are also effective as grain growth inhibitors, but more than that, VC can be used as a grain growth inhibitor even with a slight addition amount of about 0.2 to 0.5% by weight. Demonstrate the effect. That is, when the amount of VC added is less than 0.2% by weight, the effect is small, and when it exceeds 0.5% by weight, the toughness tends to deteriorate.
[0016]
On the other hand, the amount of powder of Co and / or Ni used as the binder phase needs to be 4 to 20% by weight, but if it is less than 4% by weight, it tends to deteriorate in terms of toughness and exceeds 20% by weight. It tends to be inferior in terms of wear.
[0017]
In addition to the above, the raw material mixed powder used in the present invention is composed of WC powder and inevitable impurities, but it is necessary to use ultrafine particles having an average particle diameter of WC powder in the range of 0.3 to 0.7 μm. is there. That is, when the average particle diameter of the WC powder exceeds 0.7 μm, the value of H _{RA of} 91.8 or more cannot be obtained in terms of hardness, resulting in inferior wear resistance, resulting in a decrease in life due to local wear. The object of the invention is not achieved.
[0018]
In addition, by making a uniform structure in which the difference in the average particle size between the WC powder having an average particle size of 0.3 to 0.7 μm and the heat-resistant compound powder is suppressed to within 0.1 to 0.5 μm, the wear resistance, Chipping property is further improved.
[0019]
The mixing / mixing method for preparing the raw material powder may be a normal mixing method performed by conventional powder metallurgy, for example, an appropriate amount of organic solvent (acetone, ethanol, hexane, etc.) using an attritor. Then, the blended powder and the molding aid are added and stirred, and the raw material mixed powder in the form of slurry is dried and granulated. In addition, the raw material mixed powder used in the present invention may be mixed with carbon / nitride of an element such as Hf, Zr, B or the like at a ratio of 0.1 to 5% by weight as necessary. , Contributes to heat resistance.
[0020]
The cemented carbide of the blade is obtained by sintering the raw material mixed powder as described above, but the procedure and means thereof are not particularly limited, and for example, the following method may be followed. One method is to fill a mold or rubber mold and then pressurize it with pressure or hydrostatic pressure to make a molded body, and the other is a molding aid or binder (thermoplasticity) to the dried mixed powder. Resin, lubricant, etc.) are added to make a clay, and then an extrusion molded body is produced by an injection molding machine. The material of the present invention is applicable to both molding methods. In addition, after molding, the molding aid and binder are removed, and in order to give appropriate strength, semi-sintering treatment (700-1000 ° C) is performed, and then the sintering treatment (1250-1500 ° C) is performed as it is. Then, it is finished in a predetermined shape and sintered as described above. In this case, the sintering is performed in a vacuum (1 × 10 to 1 × 10 ⁵ Torr) in the above temperature range. The sintered material is preferably subjected to HIP treatment at a temperature of 1200 to 1400 ° C. and a pressure of 100 to 2000 kg / cm ² using an inert gas (Ar, N _2, etc.) as a pressure medium.
[0021]
It is important in the present invention that the structure after sintering / HIP treatment exhibits a fine and uniform structure for both WC and heat-resistant compounds (TiC, TaC, Cr ₃ C _2, etc.). That is, when coarse grains are used, the structure shown in FIG. 2 is formed, a Co-rich phase is formed in the binder phase, damage due to chipping due to the occurrence of local wear, wear resistance deterioration due to hardness reduction, and thermal conductivity decrease. Etc. are likely to occur.
[0022]
Therefore, compared with the conventional coarse-grained P and M seed materials, the damage phenomenon as described above is likely to occur. The present invention material uses a raw material mixed powder using fine particles from the starting material and does not grow grains. Since it is manufactured by the processing method, it becomes a uniform structure as shown in FIG. 1, and it is possible to manufacture a carbide drill material (blade material) having superior wear resistance and chipping resistance.
[0023]
It is within the technical scope of the present invention that a cemented carbide cutting tool is constructed by using a cemented carbide as described above as a raw material for the blade part, using a cemented carbide having a different composition as the shank part, and joining them together. However, the structure of the cemented carbide used in the shank portion is as follows.
[0024]
It is important that the material used for the shank part has a composition that easily absorbs the cutting heat generated at the blade part. Therefore, the cutting life is extended by adopting a composition having good thermal conductivity. In order to improve the thermal conductivity, it is preferable to reduce Co and make carbide particles such as WC coarse. From this point of view, the WC powder is a coarse particle having an average particle diameter of 1 to 3 μm, and the Co and / or Ni used as a binder phase is less than 3% by weight in terms of toughness, and 9% by weight. When it exceeds, it is inferior in terms of thermal conductivity, so a composition in the range of 4 to 8% is most effective.
[0025]
In the shaft cutting tool, the blade portion and the shank portion are configured as described above, and the length ratio thereof is blade portion: shank portion = 2 to 3 × d (outer diameter): total length− (2 to 3 × d ( The outer diameter)) is optimal. This is a length that does not directly affect the cutting performance, considering the thickness of the work material. That is, when the blade portion is less than 2d, the joining interface becomes a region in direct contact with the workpiece, and damage such as boundary wear occurs, and when it exceeds 3d, the cutting heat generated in the blade portion is conducted. Therefore, the ratio range between the blade edge and the shank portion of the joined body was specified as described above.
[0026]
The joining interface between the blade part and the shank part is not planar, but it is effective to use a plurality of grooves and ridges that fit together, and the pitch interval is 0.1 to 0.3 mm. Most preferred. If the pitch is less than 0.1 mm, the effect on the thermal conductivity is small, and if it exceeds 0.3 mm, the bonding strength is lowered. That is, in the present invention, the pitch interval is defined so that the cutting heat generated in the blade portion can be easily released to the shank portion side and the function can be exhibited. The specific shapes of the plurality of grooves and ridges are not particularly limited, and the shape in a plane perpendicular to the direction in which the grooves and ridges extend includes both wavy and sawtooth shapes. It is the purpose.
[0027]
As described above, the use of an ultra-fine alloy composition for the blade provides excellent performance in wear resistance and chipping resistance and absorbs the cutting heat generated at the blade on the shank side. The cutting performance can be further improved by transmitting to a shank portion made of a cemented carbide material that is easy to heat, that is, having good thermal conductivity.
[0028]
Hereinafter, the present invention will be described in more detail by way of examples. However, the following examples are not of a nature that limits the present invention, and any design changes in accordance with the gist of the preceding and following descriptions are all within the technical scope of the present invention. Is included.
[0029]
【Example】
Reference example 1
Periodic table 4A, 5A excluding W such as WC powder having an average particle diameter of 0.5 μm, Co powder and / or Ni powder having an average particle diameter of 1.5 μm, TiC, TaC, VC, Cr ₃ C ₂ , NbC, etc. , 6A group metal carbide (heat-resistant compound), triple carbide (TiC-TaC-WC) or double carbide (TiC-TaC) powder with an average particle size of 0.7 μm, or by vibration mill or attritor Formulation compositions shown in Tables 1 and 2 were made using starting materials such as heat-resistant compound powder having a pulverized particle size of 1.0 μm or less and an average particle size of 0.8 μm.
[0030]
Each of these blended powders was put into an attritor, and an organic solvent (acetone or hexane) and a molding aid were simultaneously stirred, recovered after 5 hours, and dried and granulated. Thereafter, a molded body was molded with a predetermined mold at a pressure of 1000 kg / cm ² or more and subjected to a semi-sintering process (450 ° C. × 4 hours + 850 ° C. × 2 hours). After that, it was processed into a drill shape and sintered at 1380 ° C. for 0.5 hours in a vacuum of 1 × 10 ⁴ Torr, and further HIP-treated in an inert gas (Ar) at 1500 ° C. at 1350 ° C. did. The material properties (hardness and bending strength) after sintering and HIP treatment are shown in Tables 1 and 2.
[0031]
[Table 1]

[0032]
[Table 2]

[0033]
In order to evaluate the cutting performance of the obtained cemented carbide, it was processed into a cemented carbide drill having a diameter of 10 mm and drilled under the following conditions.
Work material: S50C
Cutting speed: 120 mm / min
Feeding: 0.25mm / rev
Cutting oil: Emulsion drill diameter: 10.0mm
Plate thickness: 1.6 x D (Drill diameter)
The cutting life was determined from the shape change of the chips, generation of cutting noise, and abnormal wear of the cutting edge. As a result, as shown in Table 3, the reference material had a life of about 2 to 3 times that of the conventional material, and as shown in FIGS. 3 and 4, the relationship between the WC grain size and the cutting life, hardness, It was clarified that the cutting life is clearly related.
[0034]
[Table 3]

[0035]
Example 1
Table 4 shows the composition and characteristics of the raw material mixed powder when the shaft cutting tool of the present invention composed of the blade portion and the shank portion is manufactured. Table 5 shows the composition and characteristics of the raw material mixed powder conventionally used. The composition of the blade portion is a powder of ultrafine particles, WC is based on 0.5 μm, and the carbide of 4A, 5A, 6A group particle size of 1.0 μm or less in the periodic table excluding W is 0.2 μm. Co and / or Ni to be added to -30% by weight and become a binder phase is in the range of 4-20% by weight. Further, VC is also added as an element for suppressing grain growth. From the above, it can be seen that the hardness value closely related to wear resistance is higher than that of the conventional material. On the other hand, the composition applied to the shank portion uses coarse particles having a WC particle size of 1 to 3 μm, and 0.1 to 5 wt% of periodic table 4A, 5A, and 6A group carbides excluding W are added, or Without addition, Co and / or Ni serving as a binder phase is in the range of 4 to 8% by weight. Therefore, the thermal conductivity is good, and the cutting heat generated by the blade portion, which is the aim of the present invention, is easily transmitted to the shank side.
[0036]
[Table 4]

[0037]
[Table 5]

[0038]
The raw material powders shown in Tables 4 and 5 were weighed and blended, mixed and dispersed with an attritor in an organic solvent, and then dried and granulated. When the obtained granulated powder is molded, the granulated powder used in the blade portion accumulated in the hopper is first put into a predetermined molding die, and then the granulated powder used in a predetermined amount of the shank portion is vibrated. The molding process was performed at a pressure of 1000 kg / cm ² or more. In this case, the length of the cutting edge is 2 to 3 × d (outer diameter), that is, the cutting edge: shank = (2 to 3 × d (outer diameter)): full length− (2 to 3 × d (outer diameter)). Each of the granulated powders was individually added so that the desired molded body was produced. The molded body is dewaxed and semi-fired, then finished to the desired material shape by semi-baking, and sintered at a temperature of 1280 to 1500 ° C. under a vacuum of 1 × 10 to 1 × 10 ⁻⁵ Torr in a vacuum furnace. Was done. Thereafter, a hot isostatic pressing process (HIP process) in which an inert gas such as Ar was used as a pressure medium and a high temperature treatment at 1200 to 1400 ° C. at a pressure of 100 to 2000 kg / cm ² was performed to obtain a material of the alloy of the present invention. .
[0039]
A cutting test was performed using the inventive material and the comparative material. The cutting test was performed using a drill (10 mmφ) and an end mill (diameter: 10 mm, 2 blades) under the following conditions. In order to make a comparison under the same conditions, the material of the present invention and the comparative material were subjected to cutting evaluation using the same coating (Al, Ti) N treated.
(Drilling conditions)
Cutting speed: 120 mm / min
Feeding: 0.25mm / rev
Plate thickness: 16mm
Work material: S50C, 50C
Cutting oil: Emulsion oil (End mill cutting conditions)
Rotation speed: 1910 rpm
Work material: SKD11
Feeding: 306mm / m (0.08mm / tooth)
Cutting depth: 1.0 mm (R) x 15 mm (L)
Cutting method: Down cut, Air blow cutting length: 6m
[0040]
The results are collectively shown in Table 6. In the cutting test using a drill, the material of the present invention has a long life of 2000 holes or more, but in the conventionally used coarse-grained drill, 300 to 400 holes. Only a lifetime is obtained. This is because the wear resistance of the carbide base material affects the cutting performance even under the same coating coating, and the material of the present invention has a composition with excellent wear resistance of the blade portion and the cutting heat generated by the shank portion at the blade portion. It seems to be the effect of acting in the direction to reduce Also in the end mill, the material according to the present invention has a value of 1/2 that of the comparative material in terms of reduced diameter wear, and it can be seen that excellent cutting performance is exhibited by the same effect as described above.
[0041]
[Table 6]

[0042]
Table 7 shows the results of examining the bending strength of the material of the present invention (No. 25). In addition, as a comparative material, it shows about the result of having investigated also about the bending strength of what joined the sintered compact of the end mill raw material (blade part: 4A) (FIG.5 (b)). Moreover, A part (bonding strength) and B part are the values measured in the position shown to Fig.5 (a). Defects such as pores and cracks are not recognized at all in the joint interface of the present invention material, and almost the same value as the blade base material or the shank part base material is obtained, which means that there is no decrease in strength due to joining. I proved it.
[0043]
[Table 7]

[0044]
【The invention's effect】
The present invention is constructed as described above, the life of the drilling and the like than conventional high life has been the axis thereof the cutting engineering tool can be realized.
[Brief description of the drawings]
FIG. 1 is an explanatory view schematically showing the structure of a cemented carbide of the present invention.
FIG. 2 is an explanatory view schematically showing the structure of a conventional cemented carbide.
FIG. 3 is a graph showing the relationship between the hardness and cutting life of each cemented carbide.
FIG. 4 is a graph showing the relationship between WC powder average particle size and cutting life of each cemented carbide.
FIG. 5 is an explanatory view showing a bending test specimen.

Claims

In a shaft cutting tool configured by joining a blade part and a shank part,
As the blade portion, the carbide powder of one or more metal elements selected from the group consisting of Group 4A, 5A, and 6A elements of the periodic table excluding W is 0.2 to 30 wt%, and Co and the binder phase Use a cemented carbide obtained by sintering WC powder having an average particle size of 0.3 to 0.7 μm and raw material mixed powder containing unavoidable impurities and / or Ni powder blended in a proportion of 4 to 20% by weight. With
As the shank portion, 0.1 to 5 wt% of carbide powder of one or more metal elements selected from the group consisting of Group 4A, 5A, and 6A elements of the periodic table excluding W, Co and / or Ni as a binder phase A shaft cutting tool characterized by using a powder of 4 to 8% by weight and a balance of sintered WC powder having an average particle size of 1 to 3 μm and raw material mixed powder which is an inevitable impurity.

2. The shaft object cutting tool according to claim 1, wherein a length ratio of the blade part and the shank part satisfies the following expression (1).
Blade part: Shank part = (2 to 3d): (Total length−Length of blade part) (1)
Where d: outer diameter

The shaft object according to claim 1 or 2, wherein a plurality of concave grooves and ridges that are fitted to each other are formed at a joint interface between the blade part and the shank part, and a pitch interval thereof is 0.1 to 0.3 mm. Cutting tools.

The cemented carbide of the blade part is a raw material mixture in which a part of carbide powder of one or more metal elements selected from the group consisting of Group 4A, 5A, and 6A elements of the periodic table is replaced with TiC-TaC-WC powder The shaft cutting tool according to any one of claims 1 to 3, wherein a powder is used.

The cemented carbide of the blade portion is a carbide powder of one or more metal elements selected from the group consisting of Group 4A, 5A, and 6A elements of the periodic table, and VC powder is in a proportion of 0. The shaft cutting tool according to any one of claims 1 to 4, wherein the raw material mixed powder contained in an amount of 2 to 0.5 wt% is used.

Cemented carbide of the cutting unit, the raw material mixture Periodic Table 4A, 5A, the average particle size of the carbide powder of at least one metal element selected from the group consisting of Group 6A element is 0.5~1.0μm The shaft cutting tool according to any one of claims 1 to 5, wherein powder is used.

The cemented carbide of the blade portion has an average particle diameter of the main WC powder and an average particle diameter of carbide powder of one or more metal elements selected from the group consisting of Group 4A, 5A, and 6A group elements of the periodic table. The shaft cutting tool according to any one of claims 1 to 6, wherein a raw material mixed powder having a difference of 0.5 µm or less is used.