JP4442944B2 - EDM method for non-conductive materials - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は、非導電性材料の放電加工方法、とくに非導電性セラミックスを放電加工するのに好適な非導電性材料の放電加工方法に関する。
【０００２】
【従来の技術】
放電加工は、被加工物と電極との間に油、水などの加工液を介して放電を発生させ、放電により生じる高熱高圧を利用して、気化、溶融により被加工物の表面を微小量づつ除去する加工方法であり、導電性の金属材料やセラミックスなど、非導電性材料の孔開け、切削などの加工に利用されている。
【０００３】
セラミックス、ガラスなどの非導電性材料（電気絶縁材料）を放電加工する場合、加工液として硝酸カリウム、塩化ナトリウムなどを含む電解液を適用し、被加工物の表面に針状電極を介して、電解ガスのコロナ放電を発生させ、放電時に生じる高熱により被加工材料を揮散させて、針状電極に対向する非導電性材料の極微小面積部分を加工する方法が知られている。
【０００４】
しかしながら、この方法においては、非導電性材料の極微小面積部分しか加工することができず、彫刻加工など、比較的広い面積部分を加工するには、きわめて大きなエネルギーを必要とするため、彫刻加工などに適用することは実用上不可能である。また、この方法においては、電解ガスが爆発を起こすというおそれもある。
【０００５】
通常のエネルギー量で安全に非導電性材料を放電加工するには、電極と被加工物である非導電性材料との間に安定した放電現象を形成することが必要であり、そのために、放電時、非導電性材料の表面に導電性を付与する方法が考えられ、非導電性材料の表面に導電性の皮膜を形成する、非導電性材料の表面をイオン注入などの手段で導電性を有する材質に改質するなどの試みがなされた。
【０００６】
しかしながら、非導電性材料の表面に金属メッキ層など導電体層を形成して放電加工を行った場合には、初期には放電が生じるが、電極に対向した非導電性材料の表面の金属メッキ層が無くなると放電が持続し難くなり、非導電性材料の表面を導電性を有する材質に改質した場合も、改質部分は加工が進行するが、改質された部分が無くなると放電が持続し難くなるという難点がある。加工すべき非導電性材料の表面に溶射、メッキなどの手段により銅、鉄などの導電体層を形成し、導電体層と電極との間に放電を発生させて導電体層の加工を行い、この導電性層が無くなると、導電体層の加工により生じたケロシンなどの加工液中の炭素および導電体層の微粒粉により形成された導電体および／または放電の熱エネルギーにより非導電性材料の表面が高温となることによって導体化されて生じた導電性層と電極との間で放電を行うようにする電気絶縁体の加工方法（特開昭６３−１５０１０９号公報）も提案されているが、この方法によっても安定した放電を持続することは必ずしも容易ではない。
【０００７】
絶縁性セラミックス皮膜を有するタービンブレードなどに孔開け加工などを行う場合、絶縁性セラミックス皮膜の表面に導電体を配設し、導電体に対向して電極を配置した後、加工液を供給しながら導電体を放電加工して貫通孔を形成し、引き続いて、この放電加工により生じた加工屑の付着堆積や含浸により絶縁性セラミックス皮膜の表面に形成された導電体層を利用して、絶縁性セラミックス皮膜に放電加工を行い微細孔を形成する方法も提案されている（特開平１０−２０２４３１号公報）が、非導電性材料の放電加工にこの方法を適用する場合には、加工面にいちいち導電体を配設しなければならないという煩わしさがあり、加工形態も限定されるという問題点がある。
【０００８】
また、本発明者の一人は、工作物表面に導電層を形成する特別の処理装置、工程を設けることなしに、絶縁体の加工を行うことができるとともに、従来不可能であった数ｍｍ〜数ｃｍの深さの深穴形状の加工を可能とする目的で「電極と被加工物間に電圧を印可しつつ加工を行う放電加工装置において、前記被加工物である絶縁物固体と前記被加工物である導電材固体とを、電極と被加工物との相対移動方向と直交する方向に機械的に密着せしめる接合手段と、前記絶縁物固体と導電物固体との接合部分と前記電極との間に放電電圧を印可する電源と、前記絶縁物固体と導電物固体と、前記電極とを、前記絶縁物固体と導電物固体との接合面に対して平行な方向に相対移動させる手段とを備えてなる放電加工装置」を提案した（特開平７−１３６８４９号公報）。しかし、絶縁物固体に接合する導電物固体は溶射や蒸着などの手段を用いる必要があり、また、放電中に導電物固体が絶縁物固体より剥離した場合には放電が持続しない場合や容易な方法で導電物固体を配置して放電加工を行うことが望まれた。
【０００９】
一方、放電加工において、放電の安定化、加工速度の向上、加工精度の向上、仕上げ面の改善などを目的として、加工液に、黒鉛、カーボンブラック、シリコン、アルミニウム、石墨などの粉末を混入して放電加工を行う方法が知られている。（特公昭３４−１２４９号公報、特公昭５２−２６３５７公報、特開平３−２７７４２１号公報、特開平６−２０６１２１号公報、特開平９−２７２０１９１号公報など）
【００１０】
上記の方法は、炭素鋼などの金属材料を加工対象とするものであるが、発明者らは、セラッミックスの放電加工についての研究を行っていく過程において、例えばグラファイトを加工液に混入して放電加工を行った場合、ある条件の下では、放電中、被加工物であるセラミックスの加工面に、加工液の分解により生じた炭化物やセラミックスとの間で形成した炭化物などからなる導電性化合物が付着して、導電性表面層を形成し、安定した放電を持続することを見出した。
【００１１】
【発明が解決しようとする課題】
本発明は、この知見に基づいてさらに実験、検討を重ねた結果としてなされたものであり、その目的は、大きなエネルギーを必要とすることなく、放電加工による金属材料の仕上げ加工に要する程度のエネルギー量で、非導電性材料、とくに、従来は微小面積を加工する場合を除いては困難であったガラスなどの酸化物系セラミックス、Ｓｉ3 Ｎ4 焼結体などの非酸化物系セラミックスのような非導電性材料の彫刻加工をも可能とする非導電性材料の放電加工方法を提供するものである。
【００１２】
上記の目的を達成するための本発明の請求項１による非導電性材料の放電加工方法は、放電加工すべき非導電性材料の表面に導電性物質を付着させた後、導電性粉末である黒鉛粉末またはカーボンブラック粉末を１０〜３０ｇ／ｌ混入した加工液を電極と前記非導電性材料との間に供給して放電加工を行うことを特徴とする。
【００１５】
請求項２による非導電性材料の放電加工方法は、請求項１記載の方法において、非導電性材料の表面に付着する導電性物質が、金属網と導電性粉末を添加した塗膜からなることを特徴とする。
【００１６】
請求項３による非導電性材料の放電加工方法は、請求項１または２記載の方法において、電極が黒鉛電極であることを特徴とし、請求項４による非導電性材料の放電加工方法は、請求項１〜３記載の方法において、電極として黒鉛電極と、銅電極または黒鉛と銅からなる複合体電極が使用されることを特徴とする。
【００１７】
発明者らの検討結果によれば、非導電性材料の放電加工において、加工液に導電性粉体を添加した場合、（１）導電性表面層は集中放電、短絡および長パルス放電などの異常放電時に形成され、被加工物表層の除去加工は正常放電時に行われる。すなわち、導電性表面層の形成と被加工物表層の除去加工が交互に行われるから加工効率が低くなる。（２）異常放電が生じるため、被加工物の表面粗さが、従来の導電性材料の放電加工で得られるものより粗くなり、加工精度も低くなることが経験された。
【００１８】
上記請求項に記載される本発明は、これらの問題点を解消するものであって、（１）放電加工の初期において、被加工物表面に導電性表面層が早期に形成される。（２）正常放電時に、導電性表面層の形成および被加工物表層の除去加工が行われる。（３）正常放電発生率が向上し、加工面粗さおよび加工速度が改善されることを特徴とする。
【００１９】
【発明の実施の形態】
本発明において、加工の対象となる非導電性材料としては、とくに、ＺｒＯ2 、Ａｌ2 Ｏ3 、ムライト（３Ａｌ2 Ｏ3 ・２ＳｉＯ2 ）、ガラスなどの酸化物系セラミックス、Ｓｉ3 Ｏ4 、ＳｉＣ、ＡｌＮ、サイアロン（Ｓｉ・Ａｌ・Ｏ・Ｎ）などの非酸化物系セラミックスなどが挙げられる。
【００２０】
本発明では、まず、放電加工すべき非導電性材料の表面に導電性物質を付着させ、ついで、導電性粉末を混入した加工液を電極と前記非導電性材料との間に供給して放電加工を行う。予め、非導電性材料の表面に付着させる導電性物質は、放電加工時に剥離しないことが必要であり、一例としては、黒鉛、カーボンブラック、α−ＳｉＣ、あるいはシリコン、アルミニウムなどの金属粉末からなる導電体の粉末を単独または混合して添加した塗料を塗布、乾燥し、必要により焼付硬化させて導電性物質の塗膜を形成する。さらに、放電加工中における放電持続を阻害する導電性物質の剥離を防止するために、導電性物質中に導電性の金属メッシュを配設するのが有効である。金属メッシュの材質としては、柔軟性をそなえた銅、銀、金、白金などがより好適であるが、鉄、鉄−ニッケル−クロム系材料（ＳＵＳ）などの金属材料を用いることもできる。金属メッシュは、篩に用いられる目開きが６０〜３６０メッシュのものが好適に使用できる。
【００２１】
加工液としては、ケロシンを主体とする加工液、その他公知のすべての加工液が適用できる。加工液に混入する導電性粉末としては、黒鉛、カーボンブラック、α−ＳｉＣの粉末、あるいはシリコン、アルミニウムなどの金属粉末が挙げられる。
【００２２】
加工液に混入する導電性粉末は、平均粒径が２〜３０μｍで固有抵抗が５０Ω・ｃｍ以下の特性を有する黒鉛粉末、α−ＳｉＣ粉末が、とくに好適に使用される。平均粒径が３０μｍを越えると、放電加工中に、短絡、集中放電などの異常放電が生じ易くなり、平均粒径は２μｍ未満では、加工速度は向上するものの被加工面の面粗さが低下する。加工液に混入する導電性粉末の固有抵抗は５０Ω・ｃｍ以下が好ましく、固有抵抗が５０Ω・ｃｍを越えると、放電加工中、被加工材料の表面に形成される導電性表面層と電極間の放電安定性が低下し易い。なお、この固有抵抗は、直径１０ｍｍ、長さ１２０ｍｍの通気性で絶縁性のアルミナ管に試料５ｇを入れ、一端より荷重を負荷し、以下の条件で４端子電圧降下法により測定し、無負荷時の電圧降下値より求める。
端子間距離（ｍｍ）：２０
設定電流値（ｍＡ）：５
負荷荷重（ｋｇ／ｃｍ2 ）：１、５、１０および１５
【００２３】
本発明による放電加工は、以下の工程に従って進行する。
（１）被加工物である非導電性材料と電極間に印可した電圧により、加工液中の導電性粉末が帯電し、電圧印可方向に並ぶ工程。
（２）並んだ導電性粉末に沿って放電する工程。
（３）放電により、被加工物の表面に導電性表面層が形成する工程。
（４）電極と導電性表面層間で安定した放電現象が生じ、被加工物表面の除去加工と導電性表面層の形成が同時に行われる工程。
【００２４】
加工液に混入する導電性粉末としては、カーボンブラックを用いることもでき、ＤＢＰ吸油量が１００ｍｌ／１００ｍｇ以上、Ｄｓｔモード径が１００ｎｍ以上の特性を有するカーボンブラックがとくに好適に使用される。ＤＢＰ吸油量が１００ｍｌ／１００ｍｇ未満、Ｄｓｔモード径が１００ｎｍ未満のものでは、上記の工程において、カーボンブラックが帯電して電圧印可方向に並び難い。カーボンブラックは、導電性を高めるために、２０００〜３０００℃の温度で熱処理を施してもよい。
【００２５】
本発明においては、加工電極として黒鉛電極を使用することにより、放電加工中、被加工物の表面への導電性表面層の形成が促進される。電極素材としては、骨材となる炭素粒子の平均粒径が２０μｍ以下のものが好ましく、１０μｍ以下のものがより好ましい。平均粒径が２０μｍを越える場合、時には１０μｍを越える場合でも、被加工物表面に消耗脱落する炭素粒子が集中放電の核となり、加工面精度を低下させる傾向がある。加工電極の消耗を少なくして加工精度を向上させるために、黒鉛電極と銅電極を使用することもできる。例えば、加工初期の１０〜２０分間は黒鉛電極を使用し、以後の加工は銅電極を使用して行う。また、銅電極に代えて黒鉛と銅との焼結複合体や含浸複合体からなる電極を使用することもできる。なお、銅電極のみを使用した場合にでも加工できるが、黒鉛電極または黒鉛複合体電極の方が酸化物系非導電性材料を放電加工し易い傾向がある。
【００２６】
本発明の作用について説明すると、電極と被加工物との間に、導電性粉体粒子を混合した加工液を存在させることにより、導電性粉体粒子が電極と被加工物との間の電力線に沿って電気泳動を行い、この現象が繰り返されることにより、一部の導電性粉体粒子群が重なり合って柱状の架橋を形成し、この架橋の部分から放電を生じる。
【００２７】
放電時に、柱状の導電性粉体粒子群は被加工物表面に飛散し、導電性表面層を形成する。被加工物となる非導電性材料の表面に導電性物質を付着させ、ついで、とくに請求項２〜３に規定する導電性粉末を混入した加工液を存在させて放電加工を行うことにより、初期に被加工物表面の導電性表面層の形成が早期に行われ、正常放電時に導電性表面層の形成および被加工物表面層の除去加工が同時に進行し、加工効率が改善される。
【００２８】
また、電極と被加工物との間に、導電性粉体粒子を混合した加工液を存在させると、前記のように、導電性粉体粒子が電極と被加工物との間の電力線に沿って電気泳動を行い、一部の導電性粉体粒子群が重なり合って柱状の架橋を形成し、この架橋の部分から放電が発生するが、この現象により、電極と被加工物との間の距離（極間距離）が広くなり加工屑の排出が容易となる。従って、短絡および集中放電などの異常放電の発生率が低減され、被加工物の加工表面粗さが改善される。
【００２９】
【実施例】
以下、本発明の実施例について説明する。
実施例１
市販のＺｒＯ2 焼結体を被加工物とし、三菱電機（株）製放電加工機（ＡＤＭＡＱ−Ｅ）を使用して放電加工を行った。加工液にはケロシン、加工液に混入する導電性粉体として、オリエンタル産業（株）製の黒鉛粉（ＦＡ−４、平均粒径：４μｍ、固有抵抗：０．３Ω・ｃｍ）、電極として東海カーボン（株）製ＨＫ−２（直径５ｍｍ）を使用した。なお、放電加工に先立って、予め、被加工物の表面に、上記の黒鉛粉（ＦＡ−４）を含有させた合成樹脂塗料を塗布し、乾燥させて導電性塗膜を形成した。加工条件および加工結果を表１に示す。
【００３０】
【表１】
表１に示すように、本発明に従って、放電加工すべき被加工物の非導電性材料の表面に導電性物質を塗着させ、ついで、導電性粉末を混入した加工液を供給して放電加工を行ったもの（試験Ｎｏ．２〜４）では、加工速度、加工面粗さの改善が認められる。試験Ｎｏ．１のものと試験Ｎｏ．２〜４のものでは、Ｒｍａｘの差は大きくないが、加工面のうねりには大きな差が観察された。
【００３２】
実施例２
市販のＳｉ3 Ｎ4 焼結体を被加工物とし、三菱電機（株）製放電加工機（ＡＤＭＡＱ−Ｅ）を使用して放電加工を行った。加工液にはケロシン、加工液に混入する導電性粉体として、オリエンタル産業（株）製の黒鉛粉（ＦＡ−４、平均粒径：４μｍ、固有抵抗：０．３Ω・ｃｍ）、電極として東海カーボン（株）製ＨＫ−２（直径５ｍｍ）を使用した。なお、放電加工に先立って、予め、被加工物の表面に、上記の黒鉛粉（ＦＡ−４）を含有させた合成樹脂塗料を塗布し、焼付け硬化させて導電性塗膜を形成した。加工条件および加工結果を表２に示す。
【００３３】
【表２】
表２に示すように、本発明に従って、放電加工すべき被加工物の非導電性材料の表面に導電性物質を塗着させ、ついで、導電性粉末を混入した加工液を供給して放電加工を行ったもの（試験Ｎｏ．６〜８）では、加工速度はやや低下したが、加工面粗さは大きく改善されている。
【００３５】
実施例３
市販のＳｉＣ焼結体を被加工物とし、三菱電機（株）製放電加工機（ＡＤＭＡＱ−Ｅ）を使用して放電加工を行った。加工液にはケロシン、加工液に混入する導電性粉体として、カーボンブラック（東海カーボン（株）製シースト９Ｈ、ＤＢＰ吸油量：１３０ｍｌ／１００ｇ、Ｄｓｔモード径：６５ｎｍ）、電極として東海カーボン（株）製ＨＫ−２（直径５ｍｍ）を使用した。なお、放電加工に先立って、予め、被加工物の表面に、上記の黒鉛粉（ＦＡ−４）を含有させた合成樹脂塗料を塗布し、焼付け硬化させて導電性塗膜を形成した。加工条件および加工結果を表３に示す。
【００３６】
【表３】
表３に示すように、本発明に従って、放電加工すべき被加工物の非導電性材料の表面に導電性物質を塗着させ、ついで、導電性粉末を混入した加工液を供給して放電加工を行ったもの（試験Ｎｏ．１０〜１２）では加工面粗さの改善が認められる。
【００３８】
実施例４
市販のＺｒＯ2 焼結体を被加工物とし、実施例と同じく三菱電機（株）製放電加工機（ＡＤＭＡＱ−Ｅ）を使用して放電加工を行った。使用電極は、加工開始から１５分間は黒鉛電極（直径５ｍｍ）を使用し、以後は銅電極（直径５ｍｍ）を使用して放電加工を行った。加工液にはケロシン、加工液に混入する導電性粉体として、平均粒径の異なるオリエンタル産業（株）製の黒鉛粉（ＦＡ−４、固有抵抗：０．３Ω・ｃｍ）を使用し、黒鉛粉の濃度を２０ｇ／ｌとして放電加工を実施した。なお、放電加工に先立って、予め、被加工物の上に１００メッシュの銅網を載置し、黒鉛粉（ＦＡ−４）を含有させた合成樹脂塗料を塗布し、乾燥させて導電性塗膜を形成した。加工条件および加工結果を表４に示す。
【００３９】
【表４】
表４に示すように、加工液に混入される黒鉛粉の平均粒径が２μｍ未満の試験Ｎｏ．１３においては、加工速度は向上しているが、加工面粗さはやや低下するものとなった。また、黒鉛粉の平均粒径が３０μｍを越える試験Ｎｏ．１７においても面粗さが低下する傾向が見られる。
【００４１】
【発明の効果】
本発明によれば、大きなエネルギーを必要とすることなく、放電加工による金属材料の仕上げ加工に要する程度のエネルギー量で、非導電性材料、とくに、従来は微小面積を加工する場合を除いては困難であったガラス、ＺｒＯ2 などの酸化物系セラミックス、Ｓｉ3 Ｎ4 焼結体などの非酸化物系セラミックスのような非導電性材料の彫刻加工をも可能とする非導電性材料の放電加工方法が提供される。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electric discharge machining method for non-conductive materials, and more particularly to an electric discharge machining method for non-conductive materials suitable for electric discharge machining of non-conductive ceramics.
[0002]
[Prior art]
In electrical discharge machining, electrical discharge is generated between the workpiece and the electrode via a working fluid such as oil or water, and the surface of the workpiece is minutely evaporated by vaporization and melting using high heat and pressure generated by the electrical discharge. It is a processing method that removes the material one after another, and is used for processing such as drilling and cutting of nonconductive materials such as conductive metal materials and ceramics.
[0003]
When non-conductive materials (electrical insulating materials) such as ceramics and glass are electrodischarge machined, an electrolytic solution containing potassium nitrate, sodium chloride, etc. is applied as the machining fluid, and the surface of the workpiece is electrolyzed via a needle electrode. A method is known in which a corona discharge of gas is generated, and a material to be processed is volatilized by high heat generated at the time of discharge to process a very small area portion of a nonconductive material facing a needle electrode.
[0004]
However, in this method, only a very small area part of a non-conductive material can be processed, and enormous energies are required to process a relatively large area part such as engraving process. It is practically impossible to apply to the above. In this method, the electrolytic gas may also explode.
[0005]
In order to safely discharge non-conductive materials with a normal amount of energy, it is necessary to form a stable discharge phenomenon between the electrode and the non-conductive material that is the work piece. In some cases, a method of imparting conductivity to the surface of the non-conductive material can be considered. A conductive film is formed on the surface of the non-conductive material, and the surface of the non-conductive material is made conductive by means such as ion implantation. Attempts have been made to improve the material.
[0006]
However, when electric discharge machining is performed by forming a conductive layer such as a metal plating layer on the surface of the nonconductive material, an electric discharge occurs in the initial stage, but the metal plating on the surface of the nonconductive material facing the electrode is performed. When the layer disappears, the discharge becomes difficult to sustain, and even when the surface of the non-conductive material is modified to a conductive material, the modified portion will continue to be processed, but if the modified portion disappears, the discharge will occur. There is a drawback that it becomes difficult to sustain. A conductor layer such as copper or iron is formed on the surface of the non-conductive material to be processed by means such as thermal spraying or plating, and a discharge is generated between the conductor layer and the electrode to process the conductor layer. When this conductive layer disappears, the non-conductive material is formed by carbon in the processing liquid such as kerosene generated by processing of the conductive layer and / or the conductor formed by the fine particles of the conductive layer and / or the thermal energy of the discharge. A method of processing an electrical insulator (Japanese Patent Laid-Open No. 63-150109) has also been proposed in which a discharge is performed between a conductive layer and an electrode, which are formed as a conductor when the surface of the metal becomes high temperature. However, it is not always easy to maintain a stable discharge even by this method.
[0007]
When drilling, etc., in a turbine blade having an insulating ceramic film, a conductor is disposed on the surface of the insulating ceramic film, an electrode is disposed opposite the conductor, and then a processing liquid is supplied. Through electrical discharge machining of the conductor to form a through hole, and subsequently using the conductor layer formed on the surface of the insulating ceramic film by depositing and impregnating machining waste generated by this electrical discharge machining, insulation There has also been proposed a method for forming fine holes by performing electric discharge machining on a ceramic film (Japanese Patent Laid-Open No. 10-202431). However, when this method is applied to electric discharge machining of a non-conductive material, the surface is processed one by one. There is a problem that it is necessary to dispose a conductor, and there is a problem that processing forms are limited.
[0008]
In addition, one of the inventors can process the insulator without providing a special processing apparatus and process for forming a conductive layer on the surface of the workpiece, and several millimeters that have been impossible in the past. For the purpose of enabling processing of a deep hole shape having a depth of several centimeters, in the electrical discharge machining apparatus that performs machining while applying a voltage between the electrode and the workpiece, the insulating solid that is the workpiece and the workpiece Bonding means for mechanically bringing a conductive material solid that is a workpiece into close contact with a direction perpendicular to the relative movement direction of the electrode and the workpiece; a bonding portion between the insulating solid and the conductive solid; and the electrode A power source that applies a discharge voltage between, a means for relatively moving the insulator solid and the conductor solid, and the electrode in a direction parallel to a joint surface between the insulator solid and the conductor solid; Has been proposed (Japanese Patent Laid-Open No. 7-1). 6849 JP). However, it is necessary to use means such as thermal spraying and vapor deposition for the conductive solid bonded to the insulating solid, and when the conductive solid is separated from the insulating solid during the discharge, the discharge does not continue or is easy. It was desired to conduct electrical discharge machining by arranging a conductive solid by the method.
[0009]
On the other hand, in electrical discharge machining, powders such as graphite, carbon black, silicon, aluminum, and graphite are mixed into the machining fluid for the purpose of stabilizing electrical discharge, improving machining speed, improving machining accuracy, and improving the finished surface. A method of performing electric discharge machining is known. (Japanese Examined Patent Publication No. 34-1249, Japanese Examined Patent Publication No. 52-26357, Japanese Unexamined Patent Publication No. 3-277421, Japanese Unexamined Patent Publication No. 6-206121, Japanese Unexamined Patent Publication No. 9-272191, etc.)
[0010]
The above method is intended for machining a metal material such as carbon steel. In the process of conducting research on ceramics electric discharge machining, the inventors have mixed, for example, graphite into the machining liquid and discharged. When processing is performed, under certain conditions, a conductive compound composed of carbide formed by decomposition of the processing liquid or carbide formed with the ceramic is formed on the processed surface of the ceramic that is the workpiece during discharge. It has been found that it adheres to form a conductive surface layer and maintains a stable discharge.
[0011]
[Problems to be solved by the invention]
The present invention has been made as a result of repeated experiments and examinations based on this knowledge, and its purpose is not to require a large amount of energy, but to the extent necessary for the finishing of a metal material by electric discharge machining. Non-conductive materials, especially oxide-based ceramics such as glass and non-oxide-based ceramics such as Si 3 N 4 sintered bodies, which were difficult to obtain except when processing a small area in the past. It is an object of the present invention to provide an electric discharge machining method for a non-conductive material that enables engraving of the non-conductive material.
[0012]
Discharge machining method of the non-conductive material according to claim 1 of the present invention for achieving the above object, after depositing a conductive material on the surface of non-conductive material to be electric discharge machining, it is a conductive powder Electrical discharge machining is performed by supplying a machining liquid in which 10 to 30 g / l of graphite powder or carbon black powder is mixed between the electrode and the non-conductive material.
[0015]
Discharge machining method of the non-conductive material according to claim 2 is the method of claim 1 Symbol placement, the conductive material adhering to the surface of non-conductive material comprises a coating film added with a metal net and a conductive powder It is characterized by that.
[0016]
The electric discharge machining method for a non-conductive material according to claim 3 is the method according to claim 1 or 2 , wherein the electrode is a graphite electrode, and the electric discharge machining method for a non-conductive material according to claim 4 The method according to any one of Items 1 to 3, wherein a graphite electrode and a copper electrode or a composite electrode made of graphite and copper are used as electrodes.
[0017]
According to the results of the study by the inventors, when electroconductive powder is added to the machining fluid in electrical discharge machining of a non-conductive material, (1) the conductive surface layer has abnormalities such as concentrated discharge, short circuit, and long pulse discharge. It is formed at the time of discharge, and the removal processing of the workpiece surface layer is performed at the time of normal discharge. That is, since the formation of the conductive surface layer and the removal process of the workpiece surface layer are performed alternately, the processing efficiency is lowered. (2) It has been experienced that since abnormal discharge occurs, the surface roughness of the workpiece becomes rougher than that obtained by the conventional electric discharge machining of the conductive material, and the machining accuracy is also lowered.
[0018]
The present invention described in the above claims solves these problems. (1) In the initial stage of electric discharge machining, a conductive surface layer is formed on the surface of the workpiece at an early stage. (2) During normal discharge, a conductive surface layer is formed and a workpiece surface layer is removed. (3) The normal discharge occurrence rate is improved, and the surface roughness and the processing speed are improved.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, non-conductive materials to be processed include, in particular, ZrO 2 , Al 2 O 3 , mullite (3Al 2 O 3 .2SiO 2 ), oxide ceramics such as glass, Si 3 O 4 , Examples thereof include non-oxide ceramics such as SiC, AlN, and sialon (Si · Al · O · N).
[0020]
In the present invention, first, a conductive substance is attached to the surface of the non-conductive material to be electro-discharge machined, and then a machining liquid mixed with electro-conductive powder is supplied between the electrode and the non-conductive material for discharging. Processing. The conductive substance to be attached to the surface of the nonconductive material in advance must not be peeled off during the electric discharge machining. For example, the conductive substance is made of graphite, carbon black, α-SiC, or metal powder such as silicon or aluminum. A coating material containing a conductive powder added alone or mixed is applied, dried, and baked and cured as necessary to form a conductive material coating. Furthermore, it is effective to dispose a conductive metal mesh in the conductive material in order to prevent peeling of the conductive material that hinders sustained discharge during electric discharge machining. As the material of the metal mesh, copper, silver, gold, platinum or the like having flexibility is more suitable, but metal materials such as iron, iron-nickel-chromium-based material (SUS) can also be used. As the metal mesh, those having an opening of 60 to 360 mesh used for the sieve can be suitably used.
[0021]
As the processing liquid, a processing liquid mainly composed of kerosene or any other known processing liquid can be applied. Examples of the conductive powder mixed in the processing liquid include graphite, carbon black, α-SiC powder, and metal powder such as silicon and aluminum.
[0022]
As the conductive powder mixed in the processing liquid, graphite powder and α-SiC powder having an average particle diameter of 2 to 30 μm and a specific resistance of 50 Ω · cm or less are particularly preferably used. If the average particle size exceeds 30 μm, abnormal discharge such as short circuit or concentrated discharge is likely to occur during electric discharge machining. If the average particle size is less than 2 μm, the processing speed is improved but the surface roughness of the processed surface is reduced. To do. The specific resistance of the conductive powder mixed in the machining fluid is preferably 50 Ω · cm or less, and when the specific resistance exceeds 50 Ω · cm, during the electric discharge machining, between the conductive surface layer formed on the surface of the material to be processed and the electrode Discharge stability tends to decrease. This specific resistance is measured by a four-terminal voltage drop method under the following conditions by placing 5 g of a sample in a breathable and insulating alumina tube having a diameter of 10 mm and a length of 120 mm, and applying a load from one end. Obtained from the voltage drop at that time.
Distance between terminals (mm): 20
Set current value (mA): 5
Applied load (kg / cm 2 ): 1, 5, 10 and 15
[0023]
The electric discharge machining according to the present invention proceeds according to the following steps.
(1) A process in which the conductive powder in the machining liquid is charged by the voltage applied between the non-conductive material that is the workpiece and the electrode, and is arranged in the voltage application direction.
(2) A step of discharging along the aligned conductive powders.
(3) A step of forming a conductive surface layer on the surface of the workpiece by electric discharge.
(4) A process in which a stable discharge phenomenon occurs between the electrode and the conductive surface layer, and the removal of the workpiece surface and the formation of the conductive surface layer are performed simultaneously.
[0024]
Carbon black can also be used as the conductive powder mixed in the processing liquid, and carbon black having the characteristics that the DBP oil absorption is 100 ml / 100 mg or more and the Dst mode diameter is 100 nm or more is particularly preferably used. In the case where the DBP oil absorption is less than 100 ml / 100 mg and the Dst mode diameter is less than 100 nm, the carbon black is charged in the above process, and it is difficult to line up in the voltage application direction. Carbon black may be subjected to heat treatment at a temperature of 2000 to 3000 ° C. in order to increase conductivity.
[0025]
In the present invention, the use of a graphite electrode as the machining electrode facilitates the formation of a conductive surface layer on the surface of the workpiece during electrical discharge machining. The electrode material preferably has an average particle diameter of carbon particles of 20 μm or less, more preferably 10 μm or less, as an aggregate. When the average particle diameter exceeds 20 μm, sometimes even when it exceeds 10 μm, carbon particles that are consumed and dropped on the surface of the workpiece tend to be the core of concentrated discharge and tend to reduce the accuracy of the processed surface. In order to reduce the consumption of the machining electrode and improve the machining accuracy, a graphite electrode and a copper electrode can also be used. For example, a graphite electrode is used for 10 to 20 minutes in the initial stage of processing, and the subsequent processing is performed using a copper electrode. Moreover, it can replace with a copper electrode and can also use the electrode which consists of a sintering composite_body | complex of graphite and copper, or an impregnation composite_body | complex. In addition, although it can process even when only a copper electrode is used, there exists a tendency for a graphite electrode or a graphite complex electrode to discharge-process an oxide type nonelectroconductive material easily.
[0026]
The operation of the present invention will be described. The power line between the electrode and the workpiece is obtained by allowing the conductive powder particles to exist between the electrode and the workpiece so that the machining liquid is mixed with the conductive powder particles. When this phenomenon is repeated, a part of the conductive powder particle groups are overlapped to form a columnar bridge, and a discharge is generated from the bridge portion.
[0027]
During discharge, the columnar conductive powder particles are scattered on the surface of the work piece to form a conductive surface layer. By attaching a conductive substance to the surface of a non-conductive material to be processed, and then performing electrical discharge machining in the presence of a processing liquid mixed with conductive powder as defined in claims 2 to 3, In addition, the formation of the conductive surface layer on the surface of the workpiece is performed at an early stage, and during the normal discharge, the formation of the conductive surface layer and the removal processing of the surface layer of the workpiece proceed simultaneously, thereby improving the processing efficiency.
[0028]
In addition, when a working fluid in which conductive powder particles are mixed is present between the electrode and the workpiece, as described above, the conductive powder particles follow the power line between the electrode and the workpiece. Electrophoresis is performed, and a part of the conductive powder particles overlap to form a columnar cross-link, and a discharge is generated from the cross-linked portion. This phenomenon causes the distance between the electrode and the workpiece. (Distance between poles) becomes wider and the processing waste can be easily discharged. Therefore, the occurrence rate of abnormal discharge such as short circuit and concentrated discharge is reduced, and the processed surface roughness of the workpiece is improved.
[0029]
【Example】
Examples of the present invention will be described below.
Example 1
A commercially available ZrO 2 sintered body was used as a workpiece, and electric discharge machining was performed using an electric discharge machine (ADMAQ-E) manufactured by Mitsubishi Electric Corporation. Kerosene is used as the processing liquid, graphite powder (FA-4, average particle size: 4 μm, specific resistance: 0.3 Ω · cm) manufactured by Oriental Sangyo Co., Ltd. as conductive powder mixed in the processing liquid, and Tokai as the electrode Carbon Co., Ltd. HK-2 (diameter 5 mm) was used. Prior to electric discharge machining, a synthetic resin coating containing the above graphite powder (FA-4) was applied in advance to the surface of the workpiece and dried to form a conductive coating film. Table 1 shows the processing conditions and processing results.
[0030]
[Table 1]
As shown in Table 1, according to the present invention, a conductive material is applied to the surface of a non-conductive material of a workpiece to be electric discharge machined, and then a machining liquid mixed with conductive powder is supplied to perform electric discharge machining. In the case of the test (test Nos. 2 to 4), improvement in the processing speed and the processing surface roughness is recognized. Test No. 1 and test no. In the cases of 2 to 4, the difference in Rmax was not large, but a large difference was observed in the waviness of the processed surface.
[0032]
Example 2
A commercially available Si 3 N 4 sintered body was used as a workpiece, and electric discharge machining was performed using an electric discharge machine (ADMAQ-E) manufactured by Mitsubishi Electric Corporation. Kerosene is used as the processing liquid, graphite powder (FA-4, average particle size: 4 μm, specific resistance: 0.3 Ω · cm) manufactured by Oriental Sangyo Co., Ltd. as conductive powder mixed in the processing liquid, and Tokai as the electrode Carbon Co., Ltd. HK-2 (diameter 5 mm) was used. Prior to electric discharge machining, a synthetic resin coating containing the above graphite powder (FA-4) was applied in advance to the surface of the workpiece, and baked and cured to form a conductive coating film. Table 2 shows the processing conditions and processing results.
[0033]
[Table 2]
As shown in Table 2, according to the present invention, a conductive material is applied to the surface of the non-conductive material of the workpiece to be electric discharge machined, and then a machining liquid mixed with conductive powder is supplied to perform electric discharge machining. In the case where the test was performed (Test Nos. 6 to 8), the processing speed was slightly reduced, but the processing surface roughness was greatly improved.
[0035]
Example 3
A commercially available SiC sintered body was used as a workpiece, and electric discharge machining was performed using an electric discharge machine (ADMAQ-E) manufactured by Mitsubishi Electric Corporation. The processing fluid is kerosene, conductive black powder mixed in the processing fluid, carbon black (Tokai Carbon Co., Ltd. Seest 9H, DBP oil absorption: 130 ml / 100 g, Dst mode diameter: 65 nm), and Tokai Carbon Co., Ltd. as the electrode. ) HK-2 (diameter 5 mm) was used. Prior to electric discharge machining, a synthetic resin coating containing the above graphite powder (FA-4) was applied in advance to the surface of the workpiece, and baked and cured to form a conductive coating film. Table 3 shows the processing conditions and the processing results.
[0036]
[Table 3]
As shown in Table 3, according to the present invention, a conductive material is applied to the surface of the non-conductive material of the workpiece to be electric discharge machined, and then a machining liquid mixed with conductive powder is supplied to perform electric discharge machining. In the case of the test (Test Nos. 10 to 12), improvement of the machined surface roughness is recognized.
[0038]
Example 4
A commercially available ZrO 2 sintered body was used as a workpiece, and electric discharge machining was performed using an electric discharge machine (ADMAQ-E) manufactured by Mitsubishi Electric Corporation in the same manner as in the examples. As the electrode used, a graphite electrode (diameter 5 mm) was used for 15 minutes from the start of machining, and thereafter, electric discharge machining was performed using a copper electrode (diameter 5 mm). Kerosene is used as the processing liquid, and graphite powder (FA-4, specific resistance: 0.3 Ω · cm) manufactured by Oriental Sangyo Co., Ltd. with different average particle diameters is used as the conductive powder mixed in the processing liquid. Electric discharge machining was carried out at a powder concentration of 20 g / l. Prior to electrical discharge machining, a 100-mesh copper mesh was previously placed on the workpiece, a synthetic resin paint containing graphite powder (FA-4) was applied, and dried to conduct conductive coating. A film was formed. Table 4 shows the processing conditions and the processing results.
[0039]
[Table 4]
As shown in Table 4, test No. 2 in which the average particle size of the graphite powder mixed in the working fluid is less than 2 μm. In No. 13, the processing speed was improved, but the processing surface roughness was slightly reduced. Test No. 1 in which the average particle size of the graphite powder exceeds 30 μm. 17 also shows a tendency for the surface roughness to decrease.
[0041]
【The invention's effect】
According to the present invention, a large amount of energy is not required, and the amount of energy required for finishing a metal material by electric discharge machining is used except for the case of processing a non-conductive material, in particular, a small area conventionally. Discharge of non-conductive materials enabling engraving of non-conductive materials such as glass, oxide ceramics such as ZrO 2, and non-oxide ceramics such as Si 3 N 4 sintered bodies A processing method is provided.
Claims (4)
Priority Applications (1)
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|---|---|---|---|
| JP07516699A JP4442944B2 (en) | 1999-03-19 | 1999-03-19 | EDM method for non-conductive materials |
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|---|---|---|---|
| JP07516699A JP4442944B2 (en) | 1999-03-19 | 1999-03-19 | EDM method for non-conductive materials |
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