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Electrochemical machining (ECM) is a method of removing metal by an electrochemical process. It is normally used for mass production and is used for working extremely hard materials or materials that are difficult to machine using conventional methods.[1] Its use is limited to electrically conductive materials. ECM can cut small or odd-shaped angles, intricate contours or cavities in extremely hard steel and exotic metals such as titanium, hastelloy, kovar, inconel and carbide. Both external and internal geometries can be machined with an electrochemical machine.

ECM is often characterized as "reverse electroplating," in that it removes material instead of adding it.[2] It is similar in concept to electrical discharge machining (EDM) in that a high current is passed between an electrode and the part, through an electrolytic material removal process having a negatively charged electrode (cathode), a conductive fluid (electrolyte), and a conductive workpiece (anode); however, in ECM there is no tool wear.[1] The ECM cutting tool is guided along the desired path close to the work but without touching the piece. Unlike EDM, however, no sparks are created. High metal removal rates are possible with ECM, with no thermal or mechanical stresses being transferred to the part, and mirror surface finishes can be achieved.

In the ECM process, a cathode (tool) is advanced into an anode (workpiece). The pressurized electrolyte is injected at a set temperature to the area being cut. The feed rate is the same as the rate of liquefaction of the material. The area between the tool and the workpiece varies within .003 in. and .030 in.[1] As electrons cross the gap, material on the workpiece is dissolved, as the tool forms the desired shape. The electrolytic fluid carries away the metal hydroxide formed in the process.[3]

As far back as 1929, an experimental ECM process was developed by W.Gussef, although it was 1959 before a commercial process was established by the Anocut Engineering Company. B.R. and J.I. Lazarenko are also credited with proposing the use of electrolysis for metal removal.[4]

Much research was done in the 1960s and 1970s, particularly in the gas turbine industry. The rise of EDM in the same period slowed ECM research in the west, although work continued behind the Iron Curtain. The original problems of poor dimensional accuracy and environmentally polluting waste have largely been overcome, although the process remains a niche technique.

The ECM process is most widely used to produce complicated shapes such as turbine blades with good surface finish in difficult to machine materials. It is also widely and effectively used as a deburring process.[5]

In deburring, ECM removes metal projections left from the machining process, and to dulls sharp edges. This process is fast and often more convenient than the conventional methods of deburring by hand or nontraditional machining processes.[1]

Contents

Advantages and Disadvantages

Because the tool does not contact the workpiece, its advantage over conventional machining is that there is no need to use expensive alloys to make the tool tougher than the workpiece. There is less tool wear in ECM, and less heat and stress are produced in processing that could damage the part. Fewer passes are typically needed, and the tool can be repeatedly used.[6]

Disadvantages are the high tooling costs of ECM, and that up to 40,000 amps of power must be applied to the workpiece. The saline electrolyte also poses the risk of corrosion to tool, workpiece and equipment.[7]

Setup and Equipment

ECM machines come in both vertical and horizontal types. Depending on the work requirements, these machines are built in many different sizes as well. The vertical machine consists of a base, column, table, and spindle head. The spindle head has a servo-mechanism that automatically advances the tool and controls the gap between the cathode (tool) and the workpiece.[1]

CNC machines of up to six axes are available.[8]

Tool Materials

Copper is often used as the electrode material. Brass, graphite, and copper-tungsten are also often used because they are easily machined, they are conductive materials, and they will not corrode.[1]

Notes

  1. ^ a b c d e f Todd, H. Robert; Allen, K. Dell; Alting, Leo (1994), Manufacturing Processes Reference Guide (1st ed.), Industrial Press Inc., p. 198-199, ISBN 0-8311-3049-0.
  2. ^ Valenti, Michael, "Making the Cut." Mechanical Engineering, American Society of Mechanical Engineers, 2001. http://www.memagazine.org/backissues/membersonly/nov01/features/makcut/makcut.html accessed 2/23/2010
  3. ^ Valenti, "Making the Cut."
  4. ^ Valenti, "Making the Cut."
  5. ^ Valenti, "Making the Cut."
  6. ^ Valenti, "Making the Cut."
  7. ^ Valenti, "Making the Cut."
  8. ^ Valenti, "Making the Cut."

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