14/09/2014
ABSTRACT FOR ELECTROCHEMICAL MACHINING:
ELECTROCHEMICAL MACHINING:
Electrochemical Machining (ECM) is a nontraditional machining process in which material is removed by the mechanism of anodic dissolution during an electrolysis process.
A d.c. voltage (10-30volts) is applied across the inter-electrode gap between pre-shaped cathode tool and an anode workpiece. The electrolyte (e.g. NACL aqueous solution) flows at high speed (10-60 m/s) through the inter-electrode gap (0.1-0.6 mm). the current density is usually 20 to 200 amperes per cm square.
The anodic dissolution rate, which is governed by faraday’s laws of electrolysis, depends on the electrochemical properties of the metal, electrolyte properties and electric current/voltage supplied.
ECM generates an approximate mirror image of the tool on the work piece. Advantages of ECM over other traditional machining processes (e.g. turning and milling) include its applicability regardless of material hardness, no tool wear, comparable high material removal rate, smooth and bright surface, and the production of components of complex geometry with stress-free and crack-free surfaces.
Therefore, ECM has been applied in many industrial applications including turbine blades, engine castings, bearing cages, gears, dies and molds and surgical implants.
Fig : Schematic illustration of the electrochemical-machining process. This process is the reverse of electroplating
• This process is reversal of the electro plating
• Electrolyte acts as current carrier
• High rate of electrolyte movement in tool work piece gap washes metal ions away from the work piece ( ANODE)
• This is washed just before they have a chance to plate on the tool ( cathode)
• Shaped tool made of brass , copper , bronze , or stainless steel
• Electrolyte is pumped at a high rate through the passages in the tool
• Machines having current capacities as high as 40,000 A and as low as 5A are available
Similarities between EDM and ECM
• The tool and workpiece are separated by a very small gap, i.e. no contact in between them is made.
• The tool and material must both be conductors of electricity.
• Needs high capital investment.
• Systems consume lots of power.
• A fluid is used as a medium between the tool and the work piece (conductive for ECM and dielectric for EDM).
• The tool is fed continuously towards the workpiece to maintain a constant gap between them (EDM may incorporate intermittent or cyclic, typically partial, tool withdrawal).
MICRO ELECTROCHEMICAL MACHINING (MicroECM)
The electrochemical machining process, when applied to the micro-machining range of applications associated with machining ultraprecision shapes with complicated geometry, is termed as micro electrochemical machining. MicroECM uses microtools that are in micron level dimensions. This micromachining technology because of its distinct advantages such as high material removal rate (MRR), better precision and control, short machining time, reliability, process flexibility, and environmental acceptability is capable of machining chemically resistant materials such as titanium, copper alloys and stainless steel, that are widely used in biomedical, electronic and other micro mechanical machining applications. In microECM—the principle of material removal is same as the conventional ECM that is by controlled anodic dissolution—the tool never touches the workpiece, nor is it consumed in the process. As a result, microECM offers an accurate, highly repeatable process with rapid machining times that produce final surface and edge. The continuous and uniform replacement of electrolyte in the gap and localization of anodic dissolution in the process of course poses some difficulties in drilling a microhole and machining 3D complex cavities that and that needs to be suitably addressed.
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