ELECTROCHEMICAL MACHINING - NON TRADITIONAL MACHINING

ELECTROCHEMICAL MACHINING

Schematic illustration of the electrochemical machining process.

PARTS MADE

(a) Turbine blade made of nickel

alloy of 360 HB. Note the

shape of the electrode on the

right.

(b) Thin slots on a 4340-steel

roller-bearing cage.

(c) Integral airfoils on a

compressor disk.

INTRODUCTION

Non-conventional machining system in which metal is removed by electrochemical process.

Characterized as ‘Reverse Electroplating’ means it removes metal instead of adding it.

Normally used for mass production and for hard materials that are difficult to machine using

conventional processes.

Both external and internal geometries can be machined.

PRINCIPLE

Faraday’s law of electrolysis : The Weight of the substance produced during electrolysis

process is directly proportional to:

Current which passes

Length of time of process.

The equivalent weight of the material

Two dissimilar metals are in contact with an electrolyte and anode loses metal to cathode.

PARTS

ANODE : Workpiece CATHODE : Tool ELECTROLYTE : An electrically conductive fluid

PARAMETERS

PARAMETERS

PROCESS

POWER SUPPLY

Available in sizes upto 10,000 amp (some

circuits are available upto 40,000amp)

Range of voltage : 2 to 30 volts d.c.

A constant voltage has to be maintained and

high density is required

ELECTROLYTE

Essential for electrolytic process.

It cools the cutting zone which becomes hot due to the flow of high current.

Neutral salts are used as electrolyte in place of highly corrosive acids and alkalies .

Electrolyte solution is pumped between the tool/workpiece gap at about 2.5 N/mm2 and 30m/s..

TOOL

REQUIREMENTS OF TOOL FOR ECM :

• Good thermal conductivity.

• Strong enough to withstand high pressures.

• It should be easily machined.

MATERIAL FOR TOOL :

Copper, Brass & Stainless steel.

OUTER INSULATION MATERIAL :

Vinyl, Teflon, epoxy, enables or high temperature varnish.

CONTROL SYSTEM

Control Parameters include:

• Voltage

• Inlet and outlet pressure of electrolyte

• Temperature of electrolyte The current is dependent on above parameters and feed rat .

ADVANTAGES

ECM is well suited for the machining of complex two-dimensional shapes

Delicate parts may be made

Difficult-to machine geometries

Poorly machinable materials may be processed

Little or no tool wear

DISADVANTAGES

Initial tooling can be timely and costly

Environmentally harmful by-products

Complicated tool design

Large power consumption

CHARACTERISTICS

Stress free grooves

Any groove geometry

Any conductive metal can be machined

Repeatable accuracy of 0.0005”

High surface finish

Fast cycle time.

The process is economical when a large no. of complex identical products are to be made.

Large cavities are more economical on ECM and can be made in 1/10th time in EDM.