JP3708087B2

JP3708087B2 - Electric discharge machine

Info

Publication number: JP3708087B2
Application number: JP2003090559A
Authority: JP
Inventors: 治樹小原; 正生村井; 章義川原
Original assignee: FANUC Corp
Current assignee: FANUC Corp
Priority date: 2003-03-28
Filing date: 2003-03-28
Publication date: 2005-10-19
Anticipated expiration: 2023-03-28
Also published as: JP2004291206A

Description

【０００１】
【発明の属する技術分野】
本発明は、放電加工機に関し、特に電食防止を図った放電加工機に関する。
【０００２】
【従来の技術】
放電加工は加工液中で被加工物と工具電極間にパルス状に電圧を印加して放電加工を行うものであるが、水を主成分とした電解性の水系加工液を用いた場合、陽極酸化などの電気化学作用によって被加工物が電食（電気化学腐食）を起こすことが知られている。例えば、被加工物が鉄系材料では、鉄のイオンＦｅ^２＋，Ｆｅ^３＋が析出され、これが加工液内の陰イオンＯＨ⁻と結合し赤錆を発生させる。又、超硬材などでは、結合材であるコバルトなどが溶出し、被加工物の断面、表面が腐食し、材質欠陥が生じることが知られている。
【０００３】
この電食を防止する方法として、被加工物と工具電極間の間隙に印加する正極性電圧パルス間の休止時間内に、正極性とは逆極性の電圧パルスを印加し、加工中の平均加工電圧が零以下となるようにすることによって、電食を防止する方法が知られている（例えば、特許文献１参照）。
【０００４】
上述した電食防止方法は加工中における電食を防止するものであり、加工後の電食を防止するものではない。被加工物を放電加工により加工する場合、長時間の加工となることから、無人で自動運転により昼夜加工が連続的に行われる場合が多い。この場合で、夜間に加工が終了したとき、被加工物は加工液中に翌朝まで放置されることになる。放電加工終了後、被加工物が長時間加工液中に浸されていると、電食が発生する場合がある。この非加工中における電食防止対策として、ワイヤ電極又は上下ノズル近傍に配置した防食電極と被加工物間に防食電源より電圧を印加し、電食を防止したものも知られている（例えば、特許文献２参照）。
【０００５】
【特許文献１】
特開昭６１−１９２４１５号公報
【特許文献２】
特開平１１−７０４１４号公報
【０００６】
【発明が解決しようとする課題】
非加工中における電食防止としては上述したように特許文献２に記載されたような方法があるが、この方法は、上下のノズル近傍に配置した防食電極又はワイヤ電極を使用する必要があり、これら電極近傍の電食を防止することしかできず、大型の被加工物などでこれら電極部と離れた箇所については電食を防止することができない。
【０００７】
そこで、本発明は、上述した問題点を改善し、非加工中において被加工物全体に亘って電食を防止する放電加工機を提供することにある。
【０００８】
【課題を解決するための手段】
本願請求項１に係わる発明は、被加工物と工具電極を水系加工液を介して対向させ、間欠的に電圧を印加して加工を行う放電加工機において、被加工物をテーブルに絶縁して取り付ける取付手段と、非加工中に被加工物とテーブルの間に接続した防食電源を備えたことを特徴とするもので、この防食電源によって印加した電圧により電食を防止するようにしたものである。又、請求項２に係わる発明は、非加工中に工具電極とテーブルとを電気的に接続するスイッチ手段を備えるようにして、工具電極と被加工物間で発生する電食をも防止するようにした。さらに、請求項３に係わる発明は、加工中のみ被加工物とテーブルとを電気的に接続するスイッチ手段を備えるようにした。また、請求項４に係わる発明は、前記防食電源を直流電源で構成するか又は平均電圧を偏向された交流電源で構成するものとした。
【０００９】
【発明の実施の形態】
水を主成分とする電解性の加工液を介して放電加工を行う放電加工機において、加工終了後に被加工物を加工液内に放置しておくと、上述したように電食が生じる。一方、異種金属との接触は電池を構成し電流が流れることが知られている。そこで、図２に示すように、水を主成分とした水系加工液１０中に被加工物２としての超硬材料のＷＣ−Ｃｏ合金を吊り下げ、該被加工物２をマイナス側に、被加工物を取り付けるテーブル（ＳＵＳ３０４）４をプラス側に接続して直流電圧を印加し、流れる電流を測定した。又、電圧を印加せず、テーブル４と被加工物２を加工液１０中で接触させることなく、テーブル４と被加工物２を導線で接続しその導線に流れる電流を測定した。電圧を印可しない状態では７０μＡ程度の電流が流れていた。これは、テーブル４と被加工物２の金属間で電池が形成され電流が流れているものと判断され、この電流が腐食を加速する原因と想定される。又、テーブル４は被加工物２との対向面積が大きく、被加工物全体に電食を発生させる要因と考えられる。
【００１０】
被加工物２とテーブル４間に電圧を印加して、この印加電圧を上昇させて流れる電流を測定した。０．４Ｖ以上まで印加電圧を上げると流れる電流の向きが逆転し、印加電圧の上昇と共に流れる電流も増加することが検出された。そこで、テーブル４と被加工物２に電圧を印加しない場合と、２Ｖの電圧を印加して７０時間放置した場合の２つの実験を行ったところ、電圧を印加しない場合にはＷＣ−Ｃｏ合金の被加工物２には電食による腐食が生じていたが、電圧を印加したＷＣ−Ｃｏ合金の被加工物２にはほとんど腐食が発生していないことが分かった。本発明は、この現象を利用して、被加工物の電食を防止する放電加工機を構成するようにしたものである。
【００１１】
図１は、本発明の一実施形態のワイヤ放電加工機の要部構成図である。
被加工物２は、金属製（例えばステンレス）のテーブル４に載置され取付手段９で絶縁体３を介して取付られる。被加工物２はスイッチ手段５を介して防食電源７のマイナス側又はテーブル４側に切替接続されるように構成されている。又、テーブル４は防食電源７のプラス側に接続され、さらに、工具電極としてのワイヤ電極１が通電子８及びスイッチ手段６を介して防食電源７のプラス側に接続されている。
防食電源７は、前述したように２Ｖ程度の直流電源又は交流電源としている。交流電源とする場合、中心電圧を＋２Ｖ程度シフトして、テーブル４に接続する側を高くし、平均電圧が＋２Ｖ程度偏向した交流電源としている。
又、被加工物２はテーブル４に対して絶縁体３により電気的に絶縁され、スイッチ手段５がテーブル側端子に接続されたとき、この被加工物２とテーブル４は短絡される構成となっている。
なお、ワイヤ電極１によって被加工物２に対して放電加工を行うための加工電源、及び該加工電源とワイヤ電極１，被加工物２の接続は従来と同様のものであり、図１では省略している。
【００１２】
放電加工を行うに際しては、スイッチ手段５、６を図１の状態とは逆の状態にする。すなわち、スイッチ手段６をオフとして、防食電源７とワイヤ電極の接続を断つ。又、スイッチ手段５を被加工物２との接続側に接続し、被加工物２とテーブル４を短絡する。そして、図示しない加工用電源からワイヤ電極１と被加工物２間にパルス状電圧を印加して加工を行う。この放電加工は従来行われている方法と同一である。
【００１３】
放電加工が終了したときには、スイッチ手段５，６を図１に示す状態にする。すなわち、スイッチ手段５を防食電源７側に接続し、且つスイッチ手段６をオンとすることによって、ワイヤ電極１と防食電源７を接続する。その結果、被加工物２は、ワイヤ電極１及びテーブル４に対して負の電位で保持され、前述したように電食が防止される。
【００１４】
なお、スイッチ手段５，６の切替は手動切替でもよいが、夜間等の無人運転による加工をも考慮すると、スイッチ手段５，６をリレースイッチ等の放電加工機の制御装置によって制御されるスイッチ手段で構成し、加工終了時には自動的に図１の状態に切替るようにする。
【００１５】
なお、上述した実施形態では、ワイヤ電極１と被加工物２間にも防食電源７より電圧を印加したが、ワイヤ電極１は放電加工終了後、自動的に切断される場合もあること、又、被加工物２との対向面積も小さいこと、逆に、テーブル４は被加工物２との対向面積の大きく、且つ近接した位置に配置されるものであるから、電食の影響はワイヤ電極１よりテーブル４の方が大きいことから、テーブル４のみを防食電極としこのテーブル４と被加工物２間にのみ防食電源７から電圧を印加するようにしてもよい。この場合、スイッチ手段６を設ける必要はない。又、ワイヤ電極１と防食電源７を接続するスイッチ手段６を設ける場合、この防食電源７を被加工物２とワイヤ電極の短絡検知用電源として利用してもよい。
【００１６】
なお、上述した実施形態ではワイヤ放電加工機の例を説明したが、加工液として水を主成分とする電解性の水系加工液を用いて加工する型彫放電加工機においても本発明は適用できるものである。
【００１７】
【発明の効果】
被加工物を長時間加工液内に放置しても、電食による腐食が防止され、被加工物の品質が保持される。そのため、夜間無人加工において、夜間に加工が終了しても、被加工物は電食による腐食が少なく、被加工物の品質が保持される。又、被加工物と接近し、対向面積が大きいテーブルを防食電極として利用することから、大型の被加工物に対しても防食効果を上げることができる。
【図面の簡単な説明】
【図１】本発明の一実施形態の要部構成図である。
【図２】電食防止のための実験例の構成を示す図である。
【符号の説明】
１ワイヤ電極
２被加工物
３絶縁体
４テーブル
５，６スイッチ手段
７防食電源
１０加工液[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electric discharge machine, and more particularly to an electric discharge machine designed to prevent electrolytic corrosion.
[0002]
[Prior art]
In electrical discharge machining, electrical discharge machining is performed by applying a voltage in a pulsed manner between the workpiece and the tool electrode in the machining fluid, but when an electrolytic aqueous machining fluid containing water as the main component is used, the anode It is known that workpieces undergo electrolytic corrosion (electrochemical corrosion) due to electrochemical action such as oxidation. For example, when the workpiece is an iron-based material, iron ions Fe ²⁺ and Fe ³⁺ are precipitated, which are combined with anions OH ⁻ in the machining liquid to generate red rust. Further, it is known that cemented carbide or the like is eluted from cemented carbide, and the cross section and surface of the workpiece are corroded to cause material defects.
[0003]
As a method of preventing this electrolytic corrosion, a voltage pulse having a polarity opposite to that of the positive polarity is applied within the pause time between the positive voltage pulses applied to the gap between the workpiece and the tool electrode, and the average machining during machining is performed. A method for preventing electrolytic corrosion by making the voltage to be equal to or less than zero is known (for example, see Patent Document 1).
[0004]
The above-described electrolytic corrosion preventing method prevents electrolytic corrosion during processing, and does not prevent electrolytic corrosion after processing. When a workpiece is machined by electric discharge machining, the machining takes a long time, and therefore, unmanned automatic operation is often performed continuously day and night. In this case, when the processing is completed at night, the workpiece is left in the processing liquid until the next morning. When the workpiece is immersed in the machining liquid for a long time after the electric discharge machining is completed, electric corrosion may occur. As a measure for preventing electrolytic corrosion during this non-processing, there is also known a method in which a voltage is applied from an anticorrosive power source between the corrosion preventing electrode disposed near the wire electrode or the upper and lower nozzles and the workpiece to prevent electrolytic corrosion (eg, Patent Document 2).
[0005]
[Patent Document 1]
JP 61-192415 A [Patent Document 2]
JP-A-11-70414 [0006]
[Problems to be solved by the invention]
As described above, there is a method as described in Patent Document 2 for preventing electric corrosion during non-processing, but this method requires the use of anticorrosion electrodes or wire electrodes arranged in the vicinity of the upper and lower nozzles, Only electrolytic corrosion in the vicinity of these electrodes can be prevented, and electrolytic corrosion cannot be prevented in places away from these electrode portions due to a large workpiece or the like.
[0007]
Accordingly, the present invention is to provide an electric discharge machine that improves the above-described problems and prevents electrolytic corrosion over the entire workpiece during non-machining.
[0008]
[Means for Solving the Problems]
The invention according to claim 1 of the present invention relates to an electric discharge machine that performs machining by applying a voltage intermittently by facing a workpiece and a tool electrode through an aqueous machining fluid, and insulating the workpiece from a table. It is characterized in that it is equipped with a mounting means to be attached and a corrosion prevention power source connected between the workpiece and the table during non-processing, and is designed to prevent electrolytic corrosion by the voltage applied by this corrosion prevention power source. is there. Further, the invention according to claim 2 is provided with a switch means for electrically connecting the tool electrode and the table during non-machining so as to prevent electric corrosion generated between the tool electrode and the workpiece. I made it. Furthermore, the invention according to claim 3 is provided with switch means for electrically connecting the workpiece and the table only during the machining. According to a fourth aspect of the present invention, the anticorrosion power source is constituted by a DC power source or an AC power source having a deflected average voltage.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
In an electric discharge machine that performs electric discharge machining using an electrolytic machining liquid containing water as a main component, if the workpiece is left in the machining liquid after the machining is completed, electrolytic corrosion occurs as described above. On the other hand, it is known that contact with a dissimilar metal constitutes a battery and current flows. Therefore, as shown in FIG. 2, a WC-Co alloy of a super hard material as a workpiece 2 is suspended in a water-based machining fluid 10 containing water as a main component, and the workpiece 2 is moved to the minus side. A table (SUS304) 4 for attaching a workpiece was connected to the plus side, a DC voltage was applied, and the flowing current was measured. Moreover, the table 4 and the workpiece 2 were connected with a conducting wire without applying a voltage, and the table 4 and the workpiece 2 were not brought into contact with each other in the machining liquid 10, and the current flowing through the conducting wire was measured. In a state where no voltage was applied, a current of about 70 μA was flowing. This is presumed that a battery is formed between the metal of the table 4 and the workpiece 2 and a current flows, and this current accelerates corrosion. Further, the table 4 has a large area facing the workpiece 2 and is considered to be a factor that causes electric corrosion on the entire workpiece.
[0010]
A voltage was applied between the workpiece 2 and the table 4, and the flowing current was measured by increasing the applied voltage. It was detected that when the applied voltage was increased to 0.4 V or higher, the direction of the flowing current was reversed, and the flowing current was increased as the applied voltage was increased. Therefore, two experiments were conducted when no voltage was applied to the table 4 and the workpiece 2 and when a voltage of 2 V was applied and left for 70 hours. When no voltage was applied, the WC-Co alloy was tested. Although it was found that the workpiece 2 was corroded by electric corrosion, the WC-Co alloy workpiece 2 to which a voltage was applied was hardly corroded. The present invention utilizes this phenomenon to constitute an electric discharge machine that prevents electrolytic corrosion of a workpiece.
[0011]
FIG. 1 is a configuration diagram of a main part of a wire electric discharge machine according to an embodiment of the present invention.
The workpiece 2 is placed on a metal (for example, stainless steel) table 4 and attached by an attachment means 9 via an insulator 3. The workpiece 2 is configured to be switched and connected to the minus side of the anticorrosion power source 7 or the table 4 side via the switch means 5. The table 4 is connected to the plus side of the anticorrosion power source 7, and the wire electrode 1 as a tool electrode is connected to the plus side of the anticorrosion power source 7 through the electronic devices 8 and the switch means 6.
As described above, the anticorrosion power source 7 is a DC power source or an AC power source of about 2V. In the case of an AC power supply, the AC voltage is shifted by about + 2V, the side connected to the table 4 is increased, and the AC power supply has an average voltage deflected by about + 2V.
Further, the workpiece 2 is electrically insulated from the table 4 by the insulator 3, and when the switch means 5 is connected to the table side terminal, the workpiece 2 and the table 4 are short-circuited. ing.
Note that the machining power source for performing electric discharge machining on the workpiece 2 by the wire electrode 1 and the connection between the machining power source and the wire electrode 1 and the workpiece 2 are the same as those in the prior art, and are omitted in FIG. are doing.
[0012]
When performing electric discharge machining, the switch means 5 and 6 are set in a state opposite to the state shown in FIG. That is, the switch means 6 is turned off, and the connection between the anticorrosion power supply 7 and the wire electrode is cut off. Further, the switch means 5 is connected to the connection side with the workpiece 2 to short-circuit the workpiece 2 and the table 4. Then, processing is performed by applying a pulse voltage between the wire electrode 1 and the workpiece 2 from a processing power source (not shown). This electric discharge machining is the same as a conventional method.
[0013]
When the electric discharge machining is completed, the switch means 5 and 6 are brought into the state shown in FIG. That is, the wire electrode 1 and the anticorrosion power supply 7 are connected by connecting the switch means 5 to the anticorrosion power supply 7 side and turning on the switch means 6. As a result, the workpiece 2 is held at a negative potential with respect to the wire electrode 1 and the table 4, and the electrolytic corrosion is prevented as described above.
[0014]
The switching of the switching means 5 and 6 may be manual switching. However, in consideration of machining by unmanned operation such as at night, the switching means 5 and 6 are controlled by a control device of an electric discharge machine such as a relay switch. 1 and automatically switches to the state shown in FIG.
[0015]
In the above-described embodiment, a voltage is applied between the wire electrode 1 and the workpiece 2 from the anticorrosion power source 7. However, the wire electrode 1 may be automatically cut after the electric discharge machining is completed. The counter area of the workpiece 2 is small, and conversely, the table 4 is arranged at a position close to the workpiece 2 and close to the workpiece 2. Since the table 4 is larger than 1, the table 4 alone may be used as the anticorrosion electrode, and the voltage may be applied from the anticorrosion power source 7 only between the table 4 and the workpiece 2. In this case, it is not necessary to provide the switch means 6. When the switch means 6 for connecting the wire electrode 1 and the anticorrosion power supply 7 is provided, the anticorrosion power supply 7 may be used as a short-circuit detection power supply for the workpiece 2 and the wire electrode.
[0016]
In the above-described embodiment, an example of a wire electric discharge machine has been described. However, the present invention can also be applied to a die-sinking electric discharge machine that uses an electrolytic aqueous machining liquid mainly composed of water as a machining liquid. Is.
[0017]
【The invention's effect】
Even if the workpiece is left in the machining liquid for a long time, corrosion due to electrolytic corrosion is prevented, and the quality of the workpiece is maintained. Therefore, in unattended night processing, even if processing is completed at night, the workpiece is less subject to corrosion due to electric corrosion, and the quality of the workpiece is maintained. Further, since a table that is close to the workpiece and has a large opposing area is used as the anticorrosion electrode, the anticorrosion effect can be improved even for a large workpiece.
[Brief description of the drawings]
FIG. 1 is a main part configuration diagram of an embodiment of the present invention.
FIG. 2 is a diagram showing a configuration of an experimental example for preventing electrolytic corrosion.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Wire electrode 2 Work piece 3 Insulator 4 Table 5, 6 Switch means 7 Anticorrosion power supply 10 Processing liquid

Claims

In an electric discharge machine that performs machining by applying a voltage intermittently with a workpiece and a tool electrode facing each other via an aqueous machining fluid, mounting means for insulating and attaching the workpiece to a table, and during non-machining An electric discharge machine comprising a corrosion-proof power source connected between a workpiece and a table.

The electric discharge machine according to claim 1, further comprising switch means for electrically connecting the tool electrode and the table during non-machining.

The electric discharge machine according to claim 1 or 2, further comprising switch means for electrically connecting the workpiece and the table only during machining.

The electric discharge machine according to any one of claims 1 to 3, wherein the anticorrosion power source is constituted by a DC power source or an AC power source whose average voltage is deflected.