Post on 09-Jan-2017
transcript
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.