31-01-2013, 04:23 PM
ELECTRO CHAMICAL MACHINING
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ABSTRACT
Electrochemical machining offers significant improvements in dimensional accuracy as compared with conventional electrochemical machining. One primary issue in electrochemical machining is to identify and control the interelectrode gap size. This paper presents an identification method for the gap size by in‐process analysis of machining current. Stochastic modeling and analysis of the current reveal two gap indicators: signal variance and damping ratio. The variance has a linear relationship with the gap size within a commonly used gap range of 0.10 to 0.20 mm for a wide range of durations. The damping ratio has been found to be highly correlated with the gap size. Laboratory experiments confirm the feasibility of this method under unevenly distributed gap conditions. The process mechanism underlying these findings is also discussed.
INTRODUCTION
• Electro chemical machining is a non conventional machining process.
• ECM was introduced by Gussef in 1929 .
• ECM is based on a controlled removal of metal by anodic dissolution in an electrolytic cell in which the work piece is anode and tool is cathode.
• Electrolysis is the process due to which chemical reaction occurs.
• Electrochemical machining has been developed initially to machine hard metals and alloys.
• Electrolytes are used as a working medium for the process.
• ECM is employed in many ways, for example, by automotive, offshore petroleum, and medical engineering industries, as well as by aerospace firms.
• ECM is based on Michael Faraday’s and Ohms laws.
Electro chemical machining process is mainly based on Michael Faraday’s following law of electrolysis-
• The amount of any substance dissolved or deposited is directly proportional to the amount of electricity which has flowed.
• The amounts of different substances deposited or dissolved by the same quantity of electricity are proportional to their chemical equivalent weights
Electrolysis is the chemical process which occurs when electric current is passed between two conductors dipped in a liquid solution(electrolyte). One conductor which is metal work piece is known as anode and another which is tool is known as cathode.
WORKING
The job to be machined is fixed in the vice in the manicuring chamber ,
that is sealed for any lekage of electrolyte and is corrosion resistant ,
having window to see machining operation. Tool is brought near the job
with the help of press buttons provided on the control panel and the table
lifting arrangement , maintaining particular gap .The tool progress is
manoeuvred vertically by servo motor and is governed by micro
controller based programmable drive. Then the prosses parameters are
set like tool feed rate ,voltage, timer.
The prosses is started in the presence of an electrolyte flow that is
Circulated with the help of pump filling gap between anode and cathode.
Electrolyte flow is adjusted by control valve.
DRAWING AND ANALYSIS
Set up consists of three sub systems-
• Machining cell
• Control panel
• Electrolyte circulation