JP3958986B2

JP3958986B2 - Material for energizing coma of wire-cut electric discharge machine, energizing coma and manufacturing method thereof

Info

Publication number: JP3958986B2
Application number: JP2002074761A
Authority: JP
Inventors: 正雄鴇田
Original assignee: Ｓｐｓシンテックス株式会社
Priority date: 2002-03-18
Filing date: 2002-03-18
Publication date: 2007-08-15
Anticipated expiration: 2022-03-18
Also published as: JP2003266248A

Description

【０００１】
【産業上の利用分野】
本発明はワイヤカット放電加工機に使用する通電電極である通電コマ用の素材及びその製造方法に関し、詳しくは、高い耐摩耗性と耐熱性を有していて従来のものに比較して寿命を著しく長くできる通電コマ用素材、通電コマ及びその製造方法に関する。
【０００２】
【従来技術】
ワイヤカット放電加工機は、主としてプレス抜き型、アルミ押し出し型、或いは引き抜きダイスなど貫通形状の金型製造用のＮＣ（数値制御）工作機械として広く金型業界では使用されている。
このようなワイヤカット放電加工機では、図１に原理が概略的に示されるように、１台の加工機に上、下隔てて２個の通電コマ１を設けてその通電コマ１を電源装置２に電気的に接続、その通電コマ１にはワイヤカット放電加工機で使用するワイヤ電極３を接触させ、ワイヤ電極３を一方向（図で矢印の方向）に所望の速度で連続的に移動させると共に、通電コマ１を介してワイヤ電極３に電源装置２を接続し、また、被加工物Ｍにも電源装置２を接続してそれらに放電加工用のパルス放電エネルギーを供給し、被加工物とワイヤ電極との間の火花放電により被加工物をスリット状に溶断するようになっている。
【０００３】
ところで、ワイヤカット放電加工機の動作中においてはワイヤ電極は常に通電コマ（給電コマ或いは給電ダイスとも呼ばれている）に接触しながら移動するものであるが、微視的に見ると、通電コマの接触面はある曲率を有する曲面で形成されているため、ワイヤ電極との接触部分には常時微少間隙が変動する状態があり、通電コマとワイヤ電極の間でも放電が繰り返されている。このため、通電コマの接触面も長期の使用により溶けてしまい、使用に耐えなくなる。このため、通電コマの材質としては、高い耐摩耗性及び耐熱性が要求され、従来においては、ＷＣ−Ｃｏ系の超硬合金材料でつくられていた。
【０００４】
しかしながら、このようなＷＣ−Ｃｏ系の超硬合金材料を使用しているにも拘わらず、従来の通電コマではその摩耗が速く、使用頻度の高いワイヤカット放電加工機のユーザーでは毎月１ないし２回、使用頻度の少ないユーザーでも３ないし４ヶ月に１回程度、通電コマを交換する必要があった。このため、元来昼夜間無人化運転が必要なＮＣワイヤカット放電加工途中で加工を中断し、段取り替え作業、再調整作業などが入って煩雑であるだけでなく、稼働率の低下及び人的作業の介入による加工誤差の発生の問題、加工精度維持上の問題、作業に熟練を要する問題等があった。
本発明者は、かかる従来の通電コマの欠点を改良すべく、その素材の面から種々研究を重ねた結果、ＷＣ−Ｃｏ系の超硬材料でもＣｏの含有量により、更には、そのＷＣ−Ｃｏ系合金材料に添加される金属元素の種類或いはその量により、その通電コマとしての耐摩耗性及び耐熱性が大きく変化することを見出した。
【０００５】
【発明が解決しようとする課題】
したがって、本発明が解決しようとする課題は、耐摩耗性及び耐熱性に優れたワイヤカット放電加工機に使用するのに適した、通電コマ用素材、通電コマ及びその製造方法を提供することである。
本発明が解決しようとする他の課題は、ＷＣ−Ｃｏ系超硬材料中のＣｏの含有量を制御すると共に、材料の焼結方法を改良することにより耐摩耗性及び耐熱性に優れた通電コマ用素材、通電コマ及びその製造方法を提供することである。
本発明が解決しようとする他の課題は、上記ＷＣ−Ｃｏ系超硬材料中に添加する他の金属元素及びその量を制御することによって、耐摩耗性及び耐熱性に優れ、長寿命の通電コマ用素材、通電コマ及びその製造方法を提供することである。
【０００６】
【課題を解決するための手段】
本願の一つの発明は、ワイヤカット放電加工機に使用する通電コマ用の素材において、
前記素材が、平均粒径０．５μｍ以下の超微粒の炭化タングステン（ＷＣ）の粉末に、コバルト（Ｃｏ）の粉末を２．０重量％以下加え、更に粉末のモリブデン（Ｍｏ）、炭化クロム（Ｃｒ₃Ｃ₂）、炭化バナジウム（ＶＣ）及び炭化ニオブ（ＮｂＣ）からなるグループから選択される少なくとも１種を所望量加えた混合粉末を、パルス通電加圧焼結によって焼結して形成されている点に特徴を有する。
上記通電コマ用の素材において、前記混合粉末の超微粒ＷＣが、１種の粒径の粉末として又は２種以上の粒径の混合粉末として配合され、Ｃｒ₃Ｃ₂の含有量が１．０重量％以下であり、Ｃｏの含有量が０重量％ないし２．０重量％の範囲であってもよく、また、前記混合粉末がＭｏ、ＶＣ及びＮｂＣを含み、それらの含有量は、それぞれ、Ｍｏが２．０重量％ないし５．５重量％、ＶＣが０．１重量％ないし０．５重量％及びＮｂＣが０．１重量％ないし０．５重量％であってもよい。
【０００７】
本願の他の発明は、ワイヤカット放電加工機用の通電コマにおいて、前記通電コマの素材が、粒径０．５μｍ以下の超微粒のＷＣの粉末に、Ｃｏの粉末を２．０重量％以下を加え、更に粉末のＭｏ、Ｃｒ₃Ｃ₂、ＶＣ及びＮｂＣからなるグループから選択される少なくとも１種を所望量加えた混合粉末を、パルス通電加圧焼結によって焼結した焼結体としてつくられ、
前記焼結体の輪郭を所望の形状に電気的及び／又は機械的加工法によりつくられて構成されている。
前記通電コマにおいて、前記混合粉末の超微粒ＷＣが、１種の粒径の粉末として又は２種以上の粒径の混合粉末として配合され、Ｃｒ₃Ｃ₂の含有量が１．０重量％以下であり、Ｃｏの含有量が０重量％ないし２．０重量％の範囲であってもよく、また、前記混合粉末がＭｏ、ＶＣ及びＮｂＣを含み、それらの含有量は、それぞれ、Ｍｏが２．０重量％ないし５．５重量％、ＶＣが０．１重量％ないし０．５重量％及びＮｂＣが０．１重量％ないし０．５重量％であってもよい。
本願の別の発明は、ワイヤカット放電加工機用の通電コマの製造方法において、
粒径０．５μｍ以下の超微粒のＷＣの粉末に、Ｃｏの粉末を２．０重量％以下を加え、更に粉末のＭｏ、Ｃｒ₃Ｃ₂、ＶＣ及びＮｂＣからなるグループから選択される少なくとも１種を所望量加えた混合粉末を、パルス通電加圧焼結によって焼結して焼結体とし、
前記焼結体を所望の輪郭形状になるように電気的及び／又は機械的加工法により切断、研磨する、
ように構成されている。
前記通電コマの製造方法において、前記焼結体を１個の前記通電コマの所望の大きさよりわずかに大きい寸法形状にパルス通電加圧焼結のニヤネットシェープ成形で多数個を同時に焼結してつくり、前記焼結体の外周を研磨して最終の通電コマ寸法形状に仕上げるようにしてもよく、或いは、前記焼結体を１個の前記通電コマに比較して大きな平板状素材としてつくり、前記平板状素材から複数の通電コマ母材をワイヤカット放電加工により切り取り、前記通電コマ母材の外周を研削、研磨するようにしてもよい。
【０００８】
【実施例】
以下、図面を参照して本発明の実施形態について説明する。
まず、通電コマ用素材（以下単に素材）の材料の組成に付いて説明する。この素材をつくるための材料も、従来の素材の材料であるＷＣ−Ｃｏ系の超硬材料である。しかしながら、この発明では、出発原料粉末の組成として、粒径０．５μｍ以下の超微粒の炭化タングステン（ＷＣ）粉末を基材として、それに、微粒のコバルト（Ｃｏ）粉末を２重量％以下（０％も含む）加え、更に、炭化バナジウム（ＶＣ）、炭化クロム（Ｃｒ₃Ｃ₂）、モリブデン（Ｍｏ）及び炭化ニオブ（ＮｂＣ）のうち１種又は２種以上をそれぞれ所望量加えて混合し、混合粉末とする。ＷＣの粒径を０．５μｍ以下としたのは、粒径がそれより大きくなると、粒界結合部分が減少するためワイヤカット放電加工機の耐電蝕性（エロージョン性）が低下する、すなわち、寿命が短くなるからである。また、Ｃｏの含有量を２重量％以下としたのは、Ｃｏの含有量がそれより多くなると、元々結合層であるコバルトはＷＣに比べて融点が低く、ワイヤカット放電加工機の通電コマとしてこのＣｏ粒子の脱落が生じ、異常摩耗が生じ易くなり耐電蝕性に劣るからである。Ｃｏの含有量は、好ましくは、０重量％ないし２．０重量％の範囲、最も好ましくは、０．５重量％ないし１．０重量％の範囲である。
【０００９】
更に、Ｍｏを加える場合には、Ｃｏ量を減じ０ないし０．５重量％とする。Ｍｏの含有量は、好ましくは、２．０重量％ないし５．５重量％の範囲、最も好ましくは、５．０重量％ないし５．５重量％の範囲である。また、ＶＣを加える場合には、その含有量が０．５重量％以下であることが望ましい。その理由は、出発原料の平均粒径０．５μｍ以下の超微粒ＷＣの粒成長を抑制する効果を大きくするためである。ＶＣの含有量は、好ましくは、０．１重量％ないし０．５重量％の範囲、最も好ましくは、０．１重量％ないし０．３重量％の範囲である。更に、Ｃｒ₃Ｃ₂を加える場合には、その含有量が１．０重量％以下であることが望ましい。その理由は、ＷＣの粒成長を抑制する効果を得るためである。Ｃｒ₃Ｃ₂の含有量は、好ましくは、０．１重量％ないし１．０重量％の範囲、最も好ましくは、０．４重量％ないし０．９重量％の範囲である。更にまた、ＮｂＣを加える場合には、その含有量が０．５重量％以下であることが望ましい。その理由は、ＮｂＣの高融点材料を添加することによりＷＣの粒成長を抑制する効果を得るためである。ＮｂＣの含有量は、好ましくは、０．１重量％ないし０．５重量％の範囲、最も好ましくは、０．１重量％ないし０．３重量％の範囲である。
【００１０】
次に、このように混合してつくった出発原料粉末から通電コマの母材をつくる場合、パルス通電加圧焼結法（パルス通電加圧焼結法とは、放電プラズマ焼結（ＳＰＳ法）、放電焼結、プラズマ活性化焼結法等を総称して呼ぶ方法である。）により焼結する。そこで、上記のように混合した原料粉末をボールミル混合機のような混合機で十分に混合し、所望の大きさ、例えば、図２に示されるような、内径Ｄ₁＝３０ｍｍの筒状の焼結型ａ内に所望の量（焼結完了後の焼結体の厚さが通電コマの厚さになる量）充填し、パルス通電加圧焼結法で焼結し、図３に示されるような円板状又は円筒状の焼結体１０をつくる。すなわち、下部にグラファイト製下パンチ部材ｃが装着されたグラファイト製焼結型ａの穴ｂの中に上記の混合材料粉末ｍを所望量充填した後、その上からグラファイト製上パンチｄを装着して用意し、そのように用意した焼結型ａを、図４に概略的に示されるように、パルス通電加圧焼結装置ｅの真空チャンバ（図示せず）の中の下通電電極ｆ上にセットし、上から上通電電極ｇで押さえた後、加圧装置ｈにより所望の圧力で加圧し、所望の真空度（例えば５〜６Ｐａ）にして、或いは不活性ガス中の状態で電源装置ｊから所望の電圧（例えば１００Ｖ以下）で、所望のパルス状の電流（例えば、４，０００ないし８，０００Ａ）を所望の時間（例えば１０ないし２０分）流して所望の焼結温度（例えば１２５０〜１８００℃）にて焼結し、焼結体すなわち素材１０にする。
【００１１】
次に、このようにしてできた焼結体１０から通電コマの母材１１をつくる場合、焼結体すなわち素材１０を、図１に示されるようなワイヤカット放電加工機により、図５で破線１２で示される切断線に沿って、所望の大きさで所望の輪郭形状（図５の例では、４側面が例えば曲率半径Ｒ（Ｒ＝４０ｍｍ）の曲面で四隅が例えば曲率半径ｒ（ｒ＝２ないし３ｍｍ）の輪郭曲線でできた一辺略１０ｍｍの略正方形）になるように、以下のようにして切断される。まず、二つの母材１１ａ及び１１ｂを連続的に切り抜く場合、実線矢印Ｘ₁ないしＸ₈にしたがって切り進んで行き、母材１１ｂの切り抜き完了直前に例えば永久磁石などで母材１１ｂの落下防止の処置を行い、母材１１ａの切り抜き完了直前で、位置Ａ近傍で素材１０と母材１１ａとが０．１〜０．２ｍｍ程度の繋ぎしろで接続されるように、切断加工作業を停止する。
一方、母材１１ａを切り抜いた後に母材１１ｂを切り抜く場合には、破線矢印Ｙ₁ないしＹ₃の順に切り進んだ後位置Ａ近傍で前述と同じ繋ぎしろを残して切断加工作業を停止し、次に位置Ｂまで逆行（切断作業を停止した状態で）させて位置Ｂから破線矢印Ｙ₄ないしＹ₆の順に切り進み、位置Ｃ近傍で前述と同程度の繋ぎしろを残して切断加工を停止する。
このようにして切断加工が済んだ素材１０をワイヤカット放電加工機から外した後、母材１１ａ、１１ｂに衝撃を与えて素材１０から母材を切り離す。切り離した母材１１の外周を研削、研磨し、必要な場合には中心に貫通穴１６を形成して通電コマ１５（図６）に仕上げられる。この通電コマ１５の外周面１７にワイヤ電極を接触させてそのワイヤ電極に電力を供給する。
【００１２】
なお、焼結体である素材１０の形状は上記のような円板状の形状の他に、例えば、一辺６０ｍｍの正方形或いは５０ｍｍ×７０ｍｍの長方形等の非円形の形状にしてもよい。このような形状の焼結体をつくる場合、焼結型を一体型の筒状の焼結型としたのでは焼結型内からの焼結体の取り出しが困難になる。そこで、焼結型を割型にして焼結体の取り出しを容易にできるようにすればよい。
また、焼結体を１個の通電コマの大きさよりわずかに大きな形状に、ニヤネットシェープ成形又は正寸法のネットシェープ成形してもよい。この場合は１個の焼結体が１個の母材を構成することになる。このような方法を採用する場合、焼結の効率を上げるために、図７に示されるように焼結型をａ′で示されるように長い筒状にし、その中に焼結材料の粉末ｍの層と粉末のグラファイトからなるスペーサ層ｎとを複数個交互に重ね、一度に複数個の母材を焼結するようにしてもよい。この場合、母材を前述の多角形状にした場合一体型の焼結型内からの焼結体すなわち母材の取り出しが困難になるので、図８に示されるように、焼結型を円周方向に複数（この実施形態では４個）の部分ａ′１ないしａ′４に分割して（分割型）、外側を押さえスリーブｋで押さえるようにし、焼結体を取り出し易くしてもよい。更に、図９［Ａ］及び［Ｂ］に示されるように、焼結型ａ″に複数（この実施形態では４個）のキャビティｂ″を一平面上に形成し、各キャビティに粉末ｍを充填し、上下パンチ部材ｄ″、ｃ″で加圧しながら複数個の母材を同時に焼結しても良い。
【００１３】
【実施例１】
出発原料の組成が、粒径０．５μｍ以下の粉末状ＷＣ９３．６重量％、同じく粒径０．５μｍ以下の粉末Ｍｏ５．５重量％、粉末Ｃｏ０．５重量％、ＶＣ０．３重量％、ＮｂＣ０．１重量％の混合粉末を用意し、ボールミル混合機により十分に混合した。この原料粉末を、内径４２ｍｍの図２に示されるような円筒状の焼結型ａ内に厚さが７．０５ｍｍになるように充填した。このように原料粉末を充填した焼結型をパルス通電加圧焼結機にセットし、下記のような条件で焼結を行い、焼結体をつくった。
焼結圧力３０〜５０ＭＰａ
焼結電圧４〜１２Ｖ
焼結電流５，０００〜８，０００Ａ
焼結温度１６５０℃
焼結時間１５〜２０分
このようにしてつくった焼結体をワイヤカット放電加工機により前述のような略正方形（仕上がり状態の通電コマより大きい略正方形に１枚の素材から４個取りする）に輪郭切断加工した後、周囲を研磨して図６に示されるような寸法の通電コマをつくった。この通電コマＡ及び従来の市販の通電コマＢについて、通電コマの耐久性の比較試験を行った。
【００１４】
［試験１］
被加工材料：ＳＫＤ−１１
被加工材寸法（ｍｍ）：１５０（幅）×１５０（長さ）×２５（厚さ）
ワイヤ線径（ｍｍ）： φ０．２ｍｍ
ワイヤ材質：ＨＢＺ（日立製真鍮線）
ワイヤ送り速度（ＷＦ）：１２ノッチ
ワイヤ張力（ＷＴ）：１２ノッチ
比抵抗（加工液／蒸留水）：２８５〜２９０μｓ
放電条件：荒加工時にコンデンサ電源を入れる（２μＦ）
加工時間：４０時間
加工条件
【表１】

ここでノッチとは、ワイヤ送り速度、ワイヤ張力を適正ワイヤセット加工条件に調節するための可変のスイッチの目盛りを意味する。
【００１５】
［試験結果と考察］
上記のような加工条件の下で４０時間連続で厚さ２５ｍｍのダイス鋼（ＳＫＤ−１１）加工試験の結果、ＳＰＳ焼結体製の通電コマではおよそ深さ１．６μｍ、幅１００μｍであるのに対して、市販の焼結体製の通電コマではおよそ深さ２．５μｍ幅２００μｍとなった。これは図９に示す拡大断面図及びそれに関連した下記の計算結果の如く、近似値の面積消耗比で約３倍の違いが観測された。ワイヤ放電加工では、通電コマに接触する真鍮ワイヤ電極は通常送り方向にワイヤテンションを受けてピンと張った状態になっているが（弓の弦のように）、被加工材とワイヤ電極との間では、ワイヤ放電加工の進行に伴い、火花放電圧力により、ある振幅で振動を受けている。この振動が電蝕幅を広げる原因となり、また微少ギャップの２電極間では火花放電が飛びやすく、これらが通電コマの溝幅を拡大する原因になっている。
Ｓ₁＝１００×１．６÷２＝８０μｍ²
Ｓ₂＝２００×２．５÷２＝２５０μｍ²
ここで、Ｓ₁は、本発明によるＳＰＳ焼結体製の通電コマの近似値面積消耗量
Ｓ₂は、市販の焼結体製の通電コマの近似値面積消耗量
面積消耗比（Ｗｓ）＝Ｓ₂÷Ｓ₁＝２５０÷８０≒３．０倍
また、加工時間とレーザ測長器で計測した溝深さの関係をグラフで表せば図１０に示されるようになる。このグラフからも明らかなようにワイヤ電極によって通電コマに形成される溝の深さは、ワイヤ放電加工時間に比例して増大し、本発明の一実施例による通電コマＡの方が従来の通電コマＢの溝よりも、４０時間の比較的長時間の使用においても浅くて済み、それだけ寿命が長くなることになる。
【００１６】
次に、より長時間の連続加工として加工時間を９０時間とし、実際のワイヤカット放電加工で使用されるＮＣ輪郭加工の直線、曲線のプログラムを変え、また、被加工材料厚さを６０ｍｍ、３０ｍｍ及び２０ｍｍと異なるダイス鋼（ＳＫＤ−１１）について荒加工条件を主として試験を行った。
［試験２］
被加工材料：ＳＫＤ−１１
被加工材料寸法（ｍｍ）：
（ａ）１５０（幅）×１５０（奥行き）×６０（厚さ）
（ｂ）１００（幅）×１００（奥行き）×３０（厚さ）
（ｃ）１００（幅）×１００（奥行き）×２０（厚さ）
ワイヤ線径（ｍｍ）： φ０．２５
ワイヤ材質：ＦＫＡ（古河電工製真鍮線）
ワイヤ送り速度（ＷＦ）：１０ノッチ
ワイヤ張力（ＷＴ）：１２ノッチ
比抵抗（加工液／蒸留水）：２８５〜２９０μｓ
放電条件：加工時にコンデンサ電源を入れる（１μＦ）
加工電圧、電流：（ａ）６０ｔｍｍ６０Ｖ、６Ａ
（ｂ）３０、２０ｔｍｍ６５Ｖ、７Ａ
加工時間９０時間
加工条件
【表２】

【００１７】
［試験結果と考察］
（１）溝幅の比較
（ａ）通電コマＡ（本発明品）：約４００μｍ
（ｂ）通電コマＢ（従来品）：約５００μｍ
（２）溝深さの比較
（ａ）通電コマＡ：８７５μｍ
（ｂ）通電コマＢ：１３０μｍ
加工試験の結果、近似値計算結果の如く、面積消耗比で約１４．９倍の違いが観測された。
ワイヤに対する通電コマの取り付け位置に若干のずれがあったが、本試験への影響は全くなかった。また、本ワイヤカット放電加工条件下において正味放電加工時間の差異は殆ど無かった。これらのワイヤ放電加工現象において、ワイヤ電極の食いつき消耗（初期摩耗）が生じると放電面積が広がることがあり、通電コマ消耗は加速される傾向にあることが推測された。高硬度面を持つ本発明による通電コマＡは従来の通電コマＢよりも放電痕が広がらず、長時間の加工に耐え、長寿命であることが立証された。この試験結果をグラフに表せば図１１に示されるようになる。本発明の一実施例による通電コマＡの方が従来の通電コマＢの溝深さよりも、９０時間の比較的長時間の使用において遙かに浅くなり、それだけ寿命が長くなることになる。
【００１８】
なお、上記実施例では略正方形の形状の通電コマを示したが、通電コマの形状はこのような形状に限られず、円筒形、長方体、ロッド状等任意の形状にすることができる。
【００１９】
【発明の効果】
本発明によれば次のような効果を奏することが可能である。
（イ）新しい組成とＳＰＳ焼結体は、従来品に比べて粒間結合強度が高いため、通電コマの耐摩耗性、耐放電エロージョン特性、耐熱性に優れ、コバルト含有の場合でもコバルトの脱落が少なく寿命の長い通電コマをつくることが可能である。
（ロ）寿命が長いので長時間加工のワイヤカット放電加工機において加工途中での段取り替え、調整作業の頻度を減少することができ、メインテナンス、無人化運転が容易になる。
（ハ）前記（ロ）と関連して、再調整頻度が少なくなり加工精度の維持確保が容易になり、稼働率を向上させランニングコストを低減し加工の信頼性向上と生産性が高まる。
（ニ）ＳＰＳニヤネットシェープ成形及び／又はネットシェープ成形により後工程の研削、研磨工程を大幅に簡略化し、通電コマの製造コストを低減することができる。
【図面の簡単な説明】
【図１】ワイヤカット放電加工機の原理を説明する図である。
【図２】本発明の通電コマを製造する焼結型の例を示す断面図である。
【図３】通電コマの母材になる焼結体の例を示す図である。
【図４】パルス通電加圧焼結方法の概略説明図である。
【図５】焼結体から通電コマのする母材を切り出す方法を説明する図である。
【図６】本実施形態の通電コマの斜視図である。
【図７】焼結型の変形例を示す断面図である。
【図８】図７の焼結型の横断面図である。
【図９】焼結型の更に別の変形例を示す図で、［Ａ］は平面図で、［Ｂ］は断面図である。
【図１０】通電コマの試験結果を説明する図である。
【図１１】４０時間の試験結果による通電コマにできた溝の深さと加工時間との関係を示すグラフ図である。
【図１２】９０時間の試験結果による通電コマにできた溝の深さと加工時間との関係を示すグラフ図である。
１０素材１１、１１ａ、１１ｂ母材
１２切断線１５通電コマ
１６貫通穴１７外周面[0001]
[Industrial application fields]
The present invention relates to a material for a current-carrying top, which is a current-carrying electrode used in a wire-cut electric discharge machine, and a method for manufacturing the same, and more specifically, has high wear resistance and heat resistance and has a longer life than conventional ones. The present invention relates to a current-carrying material, a current-carrying piece, and a method for manufacturing the same.
[0002]
[Prior art]
The wire-cut electric discharge machine is widely used in the mold industry mainly as an NC (numerical control) machine tool for manufacturing a penetrating mold such as a punching die, an aluminum extrusion die, or a drawing die.
In such a wire-cut electric discharge machine, as schematically shown in FIG. 1, two current-carrying pieces 1 are provided on a single processing machine so as to be separated from each other, and the current-carrying piece 1 is connected to a power supply device. The wire electrode 3 used in the wire-cut electric discharge machine is brought into contact with the current-carrying piece 1, and the wire electrode 3 is continuously moved at a desired speed in one direction (the direction of the arrow in the figure). In addition, the power supply device 2 is connected to the wire electrode 3 through the energization piece 1, and the power supply device 2 is also connected to the workpiece M to supply pulse discharge energy for electric discharge machining to them. The workpiece is melted in a slit shape by spark discharge between the workpiece and the wire electrode.
[0003]
By the way, during the operation of the wire-cut electric discharge machine, the wire electrode always moves while being in contact with the energizing piece (also called a feeding piece or feeding die). Since the contact surface is formed with a curved surface having a certain curvature, there is always a state in which the minute gap fluctuates at the contact portion with the wire electrode, and the discharge is repeated between the energization piece and the wire electrode. For this reason, the contact surface of the current carrying piece is also melted by long-term use, and cannot be used. For this reason, high wear resistance and heat resistance are required as the material for the current-carrying piece, and conventionally, it has been made of a WC-Co based cemented carbide material.
[0004]
However, in spite of using such a WC-Co type cemented carbide material, the wear of the conventional energizing piece is fast, and a user of a wire-cut electric discharge machine that is frequently used is 1 to 2 every month. Even if the user is less frequently used, it was necessary to change the current carrying piece once every three to four months. For this reason, machining is interrupted in the middle of NC wire cut electrical discharge machining, which originally requires unattended operation during the day and night, and not only is troublesome due to setup change work and readjustment work, but also a reduction in operating rate and human resources. There were problems such as machining errors due to work intervention, problems in maintaining machining accuracy, and problems that required skill in work.
The present inventor has conducted various studies from the viewpoint of the material to improve the drawbacks of the conventional energization piece. As a result, even in the WC-Co type super hard material, the Co content is further increased depending on the Co content. It has been found that the wear resistance and heat resistance as a current carrying piece greatly vary depending on the type or amount of metal element added to the Co-based alloy material.
[0005]
[Problems to be solved by the invention]
Therefore, the problem to be solved by the present invention is to provide a current-carrying material, a current-carrying piece, and a manufacturing method thereof suitable for use in a wire-cut electric discharge machine excellent in wear resistance and heat resistance. is there.
Another problem to be solved by the present invention is to control the content of Co in the WC-Co cemented carbide material and improve the sintering method of the material to improve the wear resistance and heat resistance. It is to provide a top material, a current-carrying top, and a manufacturing method thereof.
Another problem to be solved by the present invention is to control the other metal elements and the amount thereof added to the WC-Co cemented carbide material, thereby providing excellent wear resistance and heat resistance and having a long life. It is to provide a top material, a current-carrying top, and a manufacturing method thereof.
[0006]
[Means for Solving the Problems]
One invention of the present application is a material for a current-carrying top used in a wire cut electric discharge machine,
The raw material is an ultrafine tungsten carbide (WC) powder having an average particle size of 0.5 μm or less, and 2.0 wt% or less of cobalt (Co) powder, and further, molybdenum (Mo), chromium carbide ( Cr ₃ C ₂ ), vanadium carbide (VC) and niobium carbide (NbC) are formed by sintering a mixed powder obtained by adding a desired amount of at least one selected from the group consisting of niobium carbide (NbC) by pulsed current pressure sintering. It is characterized in that
In the material for the current carrying piece, the ultrafine WC of the mixed powder is blended as a powder having one particle size or as a mixed powder having two or more particle sizes, and the content of Cr ₃ C ₂ is 1.0. The Co content may be in the range of 0 wt% to 2.0 wt%, and the mixed powder contains Mo, VC and NbC, and their contents are respectively Mo may be 2.0 wt% to 5.5 wt%, VC may be 0.1 wt% to 0.5 wt%, and NbC may be 0.1 wt% to 0.5 wt%.
[0007]
Another invention of the present application is that, in a current-carrying piece for a wire-cut electric discharge machine, the material of the current-carrying piece is an ultrafine WC powder having a particle size of 0.5 μm or less, and Co powder is 2.0% by weight or less. In addition, a mixed powder in which a desired amount of at least one selected from the group consisting of Mo, Cr ₃ C ₂ , VC and NbC is added as a sintered body obtained by sintering by pulsed current pressure sintering. And
The contour of the sintered body is formed into a desired shape by electrical and / or mechanical processing.
In the electrification top, the ultrafine WC of the mixed powder is blended as a powder having one particle size or as a mixed powder having two or more particle sizes, and the Cr ₃ C ₂ content is 1.0% by weight or less. The Co content may be in the range of 0 wt% to 2.0 wt%, and the mixed powder contains Mo, VC, and NbC, and the content of each of them is 2 for Mo. It may be 0.0 wt% to 5.5 wt%, VC may be 0.1 wt% to 0.5 wt%, and NbC may be 0.1 wt% to 0.5 wt%.
Another invention of the present application is a method for manufacturing a current-carrying piece for a wire-cut electric discharge machine,
At least one selected from the group consisting of Mo, Cr ₃ C ₂ , VC, and NbC is added to a powder of Co in an ultrafine WC powder with a particle size of 0.5 μm or less, and 2.0 wt% or less of Co powder. The mixed powder to which a desired amount of seeds is added is sintered by pulsed current pressure sintering to form a sintered body,
The sintered body is cut and polished by an electrical and / or mechanical processing method so as to have a desired contour shape,
It is configured as follows.
In the method of manufacturing the current-carrying piece, a plurality of the sintered bodies are sintered at the same time to a shape slightly larger than a desired size of the one current-carrying piece by near-net shape forming of pulsed current pressure sintering. The outer periphery of the sintered body may be polished to finish to the final energized piece size shape, or the sintered body may be made as a large flat plate material compared to one energized piece, A plurality of energized piece base materials may be cut from the flat plate material by wire-cut electric discharge machining, and the outer periphery of the energized piece base material may be ground and polished.
[0008]
【Example】
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, the composition of the material for the current carrying piece (hereinafter simply referred to as “material”) will be described. The material for making this material is also a conventional WC-Co based carbide material. However, according to the present invention, the composition of the starting material powder is based on an ultrafine tungsten carbide (WC) powder having a particle size of 0.5 μm or less as a base material, and fine cobalt (Co) powder is 2 wt% or less (0 In addition, one or more of vanadium carbide (VC), chromium carbide (Cr ₃ C ₂ ), molybdenum (Mo) and niobium carbide (NbC) are added in desired amounts and mixed. Mix powder. The reason why the WC particle size is 0.5 μm or less is that when the particle size is larger than that, the grain boundary bonding portion is reduced, so that the electric corrosion resistance (erosion property) of the wire-cut electric discharge machine is lowered. Because it becomes shorter. In addition, the Co content is set to 2% by weight or less because when the Co content is more than that, cobalt, which is originally a bonding layer, has a lower melting point than WC, and serves as an energizing piece for a wire-cut electric discharge machine. This is because the Co particles fall off, and abnormal wear tends to occur, resulting in poor corrosion resistance. The Co content is preferably in the range of 0 wt% to 2.0 wt%, most preferably in the range of 0.5 wt% to 1.0 wt%.
[0009]
Furthermore, when adding Mo, the amount of Co is reduced to 0 to 0.5% by weight. The Mo content is preferably in the range of 2.0 wt% to 5.5 wt%, most preferably in the range of 5.0 wt% to 5.5 wt%. Moreover, when adding VC, it is desirable that the content is 0.5 weight% or less. The reason for this is to increase the effect of suppressing the grain growth of the ultrafine WC having an average grain size of 0.5 μm or less of the starting material. The VC content is preferably in the range of 0.1 wt% to 0.5 wt%, most preferably in the range of 0.1 wt% to 0.3 wt%. Further, if adding Cr ₃ C _2, it is preferable that the content is 1.0 wt% or less. The reason is to obtain an effect of suppressing grain growth of WC. The content of Cr ₃ C ₂ is preferably in the range of 0.1 wt% to 1.0 wt%, most preferably in the range of 0.4 wt% to 0.9 wt%. Furthermore, when NbC is added, the content is desirably 0.5% by weight or less. The reason is to obtain an effect of suppressing grain growth of WC by adding a high melting point material of NbC. The NbC content is preferably in the range of 0.1 wt% to 0.5 wt%, most preferably in the range of 0.1 wt% to 0.3 wt%.
[0010]
Next, when making the base material of the current carrying piece from the starting raw material powder produced by mixing in this way, the pulse current pressure sintering method (the pulse current pressure sintering method is the spark plasma sintering (SPS method)) The discharge sintering, the plasma activated sintering method, etc. are collectively referred to.). Therefore, the raw material powders mixed as described above are sufficiently mixed with a mixer such as a ball mill mixer, and a desired size, for example, as shown in FIG. 2, a cylindrical firing with an inner diameter D ₁ = 30 mm. A desired amount (the amount in which the thickness of the sintered body after the completion of sintering becomes the thickness of the current-carrying piece) is filled in the mold a, and sintered by the pulse current pressure sintering method, as shown in FIG. Such a disk-shaped or cylindrical sintered body 10 is produced. That is, after a desired amount of the mixed material powder m is filled in the hole b of the graphite sintering die a having a graphite lower punch member c attached to the lower portion, a graphite upper punch d is mounted thereon. As shown schematically in FIG. 4, the thus prepared sintering mold a is placed on the lower energizing electrode f in the vacuum chamber (not shown) of the pulse energizing pressure sintering apparatus e. After being pressed by the upper energizing electrode g from above, the power supply device is pressurized at a desired pressure by the pressurizing device h to a desired degree of vacuum (for example, 5 to 6 Pa) or in a state of inert gas. From j, a desired pulsed current (eg, 4,000 to 8,000 A) is passed for a desired time (eg, 10 to 20 minutes) at a desired voltage (eg, 100 V or less), and a desired sintering temperature (eg, 1250). Sintered at ~ 1800 ° C) To sintered body or material 10.
[0011]
Next, when the base material 11 of the current carrying piece is made from the sintered body 10 made in this way, the sintered body, that is, the material 10 is broken by a broken line in FIG. 5 using a wire-cut electric discharge machine as shown in FIG. 12 along the cutting line 12 and a desired contour shape with a desired size (in the example of FIG. 5, the four side surfaces are curved surfaces having a curvature radius R (R = 40 mm) and the four corners are, for example, curvature radii r (r = r = 2 to 3 mm) and is cut in the following manner so as to form an approximately square with a side of approximately 10 mm. First, the two when cutting out the

base material

11a and 11b successively, to no solid arrows X ₁ went a cut according to X _8, and more at cutout immediately before completion, for example, the permanent magnets of the base material 11b of the fall prevention of the base material 11b The treatment is performed, and the cutting work is stopped immediately before completion of the cutting of the base material 11a so that the material 10 and the base material 11a are connected in the vicinity of the position A with a joining margin of about 0.1 to 0.2 mm.
On the other hand, in the case of cutting the base material 11b after cutting the base material 11a, the cutting work is stopped leaving the same joining margin in the vicinity of the position A in the vicinity of the position A after cutting in the order of broken line arrows Y ₁ to Y ₃ . Next, go back to position B (with the cutting operation stopped), and proceed from position B in the order of dashed arrows Y ₄ to Y ₆ , and stop cutting while leaving the same margin as above in the vicinity of position C. To do.
After the material 10 that has been cut in this way is removed from the wire-cut electric discharge machine, the

base material

11a, 11b is impacted to separate the base material from the material 10. The outer periphery of the separated base material 11 is ground and polished, and if necessary, a through hole 16 is formed at the center to finish the current piece 15 (FIG. 6). A wire electrode is brought into contact with the outer peripheral surface 17 of the energization piece 15 to supply electric power to the wire electrode.
[0012]
In addition, the shape of the raw material 10 which is a sintered body may be a non-circular shape such as a square with a side of 60 mm or a rectangle with a size of 50 mm × 70 mm, for example, in addition to the disk shape as described above. In the case of producing a sintered body having such a shape, it is difficult to take out the sintered body from the inside of the sintering mold if the sintering mold is an integral cylindrical sintering mold. Therefore, the sintered mold may be split so that the sintered body can be easily taken out.
Alternatively, the sintered body may be formed into a shape slightly larger than the size of one current carrying piece, or may be formed into a net shape or a net shape having a positive dimension. In this case, one sintered body constitutes one base material. When such a method is employed, in order to increase the efficiency of the sintering, the sintering mold is formed into a long cylinder as shown by a ′ as shown in FIG. And a plurality of spacer layers n made of powdered graphite may be alternately stacked to sinter a plurality of base materials at a time. In this case, since it becomes difficult to take out the sintered body, that is, the base material from the integrated sintering die when the base material has the polygonal shape described above, as shown in FIG. It may be divided into a plurality of (four in this embodiment) portions a′1 to a′4 in the direction (divided type), and the outer side may be pressed by the pressing sleeve k to facilitate removal of the sintered body. Further, as shown in FIGS. 9A and 9B, a plurality of (four in this embodiment) cavities b ″ are formed on one plane in the sintering mold a ″, and the powder m is put in each cavity. A plurality of base materials may be sintered at the same time while filling and pressing with upper and lower punch members d ″ and c ″.
[0013]
[Example 1]
The composition of the starting material is powdery WC 93.6% by weight with a particle size of 0.5 μm or less, 5.5% by weight of powder Mo with a particle size of 0.5 μm or less, 0.5% by weight of powder Co, 0.3% by weight of VC, NbC0 A 1% by weight mixed powder was prepared and thoroughly mixed with a ball mill mixer. This raw material powder was filled into a cylindrical sintering mold a having an inner diameter of 42 mm as shown in FIG. The sintering mold filled with the raw material powder was set in a pulse current pressure sintering machine and sintered under the following conditions to produce a sintered body.
Sintering pressure 30-50MPa
Sintering voltage 4-12V
Sintering current 5,000-8,000A
Sintering temperature 1650 ° C
Sintering time 15 to 20 minutes The sintered body made in this way is approximately square as described above using a wire-cut electric discharge machine (takes four from a single material into approximately squares larger than the finished energized coma). After cutting the outline, the periphery was polished to produce a current carrying piece having dimensions as shown in FIG. With respect to this energization piece A and a conventional commercially available energization piece B, a comparative test of the durability of the energization piece was performed.
[0014]
[Test 1]
Work material: SKD-11
Workpiece dimensions (mm): 150 (width) x 150 (length) x 25 (thickness)
Wire diameter (mm): φ0.2mm
Wire material: HBZ (Hitachi brass wire)
Wire feed rate (WF): 12 notch wire tension (WT): 12 notch specific resistance (working fluid / distilled water): 285-290 μs
Discharge condition: Turn on the capacitor power during roughing (2μF)
Processing time: 40 hours processing conditions [Table 1]

Here, the notch means a scale of a variable switch for adjusting the wire feed speed and the wire tension to the proper wire set processing conditions.
[0015]
[Test results and discussion]
As a result of a 25 mm-thick die steel (SKD-11) processing test for 40 hours under the above processing conditions, the SPS sintered body has a depth of about 1.6 μm and a width of about 100 μm. On the other hand, the current-carrying piece made of a commercially available sintered body has a depth of about 2.5 μm and a width of 200 μm. As shown in the enlarged cross-sectional view shown in FIG. 9 and the following calculation result related thereto, a difference of about three times was observed in the approximate area wear ratio. In wire electric discharge machining, the brass wire electrode in contact with the current-carrying piece is usually in tension with the wire tension in the feed direction (like a bowstring), but between the workpiece and the wire electrode. Then, with the progress of wire electric discharge machining, vibration is received with a certain amplitude due to the spark discharge pressure. This vibration causes the electric corrosion width to widen, and spark discharge easily occurs between the two electrodes with a minute gap, which causes the groove width of the current carrying piece to be increased.
S ₁ = 100 × 1.6 ÷ 2 = 80 μm ²
S ₂ = 200 × 2.5 ÷ 2 = 250 μm ²
Here, S ₁ is the approximate area consumption amount S ₂ of the current-carrying piece made of the SPS sintered body according to the present invention, and S ₂ is the approximate value area consumption amount area consumption ratio (Ws) = S ₂ ÷ S ₁ = 250 ÷ 80≈3.0 times Further, if the relationship between the machining time and the groove depth measured by the laser length measuring device is represented by a graph, it is as shown in FIG. As apparent from this graph, the depth of the groove formed in the energization piece by the wire electrode increases in proportion to the wire electric discharge machining time, and the energization piece A according to the embodiment of the present invention is more conventional. Compared with the groove of the frame B, it can be shallower even when used for a relatively long time of 40 hours, and the lifetime is increased accordingly.
[0016]
Next, the machining time is set to 90 hours for longer continuous machining, the NC contour machining straight line and curve programs used in actual wire-cut electric discharge machining are changed, and the material thickness to be machined is 60 mm and 30 mm. And the test was mainly conducted on roughing conditions for die steel (SKD-11) different from 20 mm.
[Test 2]
Work material: SKD-11
Work material dimensions (mm):
(A) 150 (width) x 150 (depth) x 60 (thickness)
(B) 100 (width) x 100 (depth) x 30 (thickness)
(C) 100 (width) x 100 (depth) x 20 (thickness)
Wire diameter (mm): φ0.25
Wire material: FKA (Furukawa Electric brass wire)
Wire feed rate (WF): 10 notch wire tension (WT): 12 notch specific resistance (working fluid / distilled water): 285-290 μs
Discharge condition: Turn on the capacitor power supply during processing (1μF)
Processing voltage, current: (a) 60tmm 60V, 6A
(B) 30, 20tmm 65V, 7A
Machining time 90 hours Machining conditions [Table 2]

[0017]
[Test results and discussion]
(1) Comparison of groove width (a) Energizing piece A (product of the present invention): about 400 μm
(B) Energizing piece B (conventional product): approx. 500 μm
(2) Comparison of groove depth (a) Energizing piece A: 875 μm
(B) Energization top B: 130 μm
As a result of the processing test, as shown in the approximate value calculation result, a difference of about 14.9 times in the area consumption ratio was observed.
There was a slight shift in the mounting position of the current carrying piece to the wire, but there was no effect on this test. Moreover, there was almost no difference in the net electric discharge machining time under the wire cut electric discharge machining conditions. In these wire electric discharge machining phenomena, it is speculated that when the bite wear (initial wear) of the wire electrode occurs, the discharge area may be widened, and the commutation combustion tends to be accelerated. It has been proved that the current-carrying piece A according to the present invention having a high hardness surface has less discharge traces than the conventional current-carrying piece B, can withstand long-time processing, and has a long life. If this test result is represented in a graph, it will be as shown in FIG. The energizing piece A according to an embodiment of the present invention is much shallower than the conventional energizing piece B in the use for a relatively long time of 90 hours, and the life is increased accordingly.
[0018]
In addition, although the substantially square-shaped energization piece was shown in the said Example, the shape of an energization piece is not restricted to such a shape, It can be made into arbitrary shapes, such as a cylindrical shape, a rectangular parallelepiped, and a rod shape.
[0019]
【The invention's effect】
According to the present invention, the following effects can be obtained.
(A) The new composition and the SPS sintered body have higher intergranular bond strength compared to the conventional products, so it has excellent wear resistance, discharge erosion resistance, and heat resistance of the current carrying top, and even when cobalt is contained, the cobalt is removed. It is possible to make a current-carrying piece with little life.
(B) Since the service life is long, it is possible to reduce the frequency of setup change and adjustment work during machining in a wire-cut electric discharge machine for long machining, and maintenance and unmanned operation are facilitated.
(C) In relation to (b), the readjustment frequency is reduced and it is easy to maintain and ensure machining accuracy, the operating rate is increased, the running cost is reduced, the machining reliability is improved, and the productivity is increased.
(D) SPS near net shape molding and / or net shape molding can greatly simplify the subsequent grinding and polishing steps, and reduce the manufacturing cost of the current carrying pieces.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining the principle of a wire cut electric discharge machine.
FIG. 2 is a cross-sectional view showing an example of a sintered mold for producing a current-carrying piece of the present invention.
FIG. 3 is a view showing an example of a sintered body that becomes a base material of a current carrying piece.
FIG. 4 is a schematic explanatory diagram of a pulse current pressure sintering method.
FIG. 5 is a diagram for explaining a method of cutting out a base material to be energized from a sintered body.
FIG. 6 is a perspective view of an energization piece of the present embodiment.
FIG. 7 is a cross-sectional view showing a modified example of a sintered mold.
8 is a cross-sectional view of the sintered mold of FIG.
FIGS. 9A and 9B are views showing still another modified example of the sintered mold, in which [A] is a plan view and [B] is a cross-sectional view.
FIG. 10 is a diagram for explaining a test result of energized frames.
FIG. 11 is a graph showing the relationship between the depth of a groove formed in a current-carrying piece and the processing time based on a 40-hour test result.
FIG. 12 is a graph showing the relationship between the depth of a groove formed in a current-carrying piece and the processing time based on a 90-hour test result.
DESCRIPTION OF SYMBOLS 10

Material

11, 11a, 11b Base material 12 Cutting line 15 Current carrying piece 16 Through hole 17 Outer peripheral surface

Claims

In the material for energizing tops used in wire cut electrical discharge machines,
The raw material is an ultrafine tungsten carbide (WC) powder having an average particle size of 0.5 μm or less, and 2.0 wt% or less of cobalt (Co) powder, and further, molybdenum (Mo), chromium carbide ( Cr ₃ C ₂ ), vanadium carbide (VC) and niobium carbide (NbC) are formed by sintering a mixed powder obtained by adding a desired amount of at least one selected from the group consisting of niobium carbide (NbC) by pulsed current pressure sintering. A material for energizing coma characterized by

2. The material for a current carrying piece according to claim 1, wherein the ultrafine WC of the mixed powder is blended as a powder having one particle size or a mixed powder having two or more particle sizes, and contains Cr ₃ C ₂ . A current-carrying top material having an amount of 1.0 wt% or less and a Co content in the range of 0 wt% to 2.0 wt%.

3. The material for energizing coma according to claim 1 or 2, wherein the mixed powder contains Mo, VC and NbC, and the contents thereof are Mo 2.0% to 5.5% by weight, VC, respectively. Is 0.1 wt% to 0.5 wt% and NbC is 0.1 wt% to 0.5 wt%.

In energization top for wire cut electric discharge machine,
The material for the current carrying piece is made of super fine WC powder having a particle size of 0.5 μm or less, and 2.0% by weight or less of Co powder is added, and further consists of powdered Mo, Cr ₃ C ₂ , VC and NbC. A mixed powder obtained by adding a desired amount of at least one selected from the group is produced as a sintered body obtained by sintering by pulsed current pressure sintering,
An energization piece characterized in that the contour of the sintered body is formed into a desired shape by electrical and / or mechanical processing.

5. The energization top according to claim 4, wherein the ultrafine WC of the mixed powder is blended as a powder having one particle size or as a mixed powder having two or more particle sizes, and the content of Cr ₃ C ₂ is 1 An energization coma having a Co content of 0 wt% or less and a Co content in the range of 0 wt% to 2.0 wt%.

6. The current carrying piece according to claim 4 or 5, wherein the mixed powder contains Mo, VC and NbC, and the contents thereof are respectively 2.0 wt% to 5.5 wt% for Mo and 0.5 wt% for VC. A current-carrying top having 1 wt% to 0.5 wt% and NbC of 0.1 wt% to 0.5 wt%.

In the manufacturing method of the current carrying piece for the wire cut electric discharge machine,
At least one selected from the group consisting of Mo, Cr ₃ C ₂ , VC, and NbC is added to a powder of Co in an ultrafine WC powder with a particle size of 0.5 μm or less, and 2.0 wt% or less of Co powder. The mixed powder to which a desired amount of seeds is added is sintered by pulsed current pressure sintering to form a sintered body,
The sintered body is cut and polished by an electrical and / or mechanical processing method so as to have a desired contour shape,
A method for manufacturing a current-carrying piece.

In the manufacturing method of the electricity supply top of Claim 7,
The sintered body is formed by simultaneously sintering a large number of pieces into a shape slightly larger than the desired size of one of the current-carrying pieces by near-net shaping of pulsed current pressure sintering,
The outer periphery of the sintered body is polished and finished to the final energized frame size shape,
A method for manufacturing a current-carrying piece.

In the manufacturing method of the electricity supply top of Claim 7,
Making the sintered body as a large flat plate material compared to one energizing piece,
A plurality of energized piece base materials are cut from the flat plate material by wire cut electric discharge machining,
Grinding and polishing the outer periphery of the energization piece base material,
A method for manufacturing a current-carrying piece.