Electrochemical Honing – Working, Advantages, Disadvantages and Applications

Electrochemical Honing is a process in which material is removed with help of electrical energy, chemical energy and honing process.

For those who don’t know, honing is an abrasive machining process that produces a precision surface on a metal workpiece by scrubbing an abrasive stone against it along a controlled path.
In honing a hone tool is used. A hone tool is a tool that simultaneously rotates as well as translates.

High metal removal rates are possible with ECH, with no thermal or mechanical stresses and mirror surface finish can be achieved.

In an ECH process, a DC Power Supply is used of which the tool act as the cathode and the workpiece act as anode.
The pressirized electrolyte is injected to the area being cut at a set temperature. The feed rate is same as the rate of liquefaction of the material or the rate of conversion of material into a liquid state.
In this process, the gap between the tool and the workpiece varies between 80-800 micrometers (.003 in. and .030 in.).
As electrons cross the gap, material from the workpiece is dissolved as the tool forms the desired shape in workpiece.
The metal hydroxide formed during the process is carried away by the electrolytic fluid.

Honing Tool:
The honing tool is composed of abrasive grains that are bound together with an adhesive.
Generally hone grains are irregular shaped and about 10 to 50 micrometers in diameter ( 300 to 1500 mesh grit).
Smoother surface is produced if small grain sizes are used.
Honing tools are more friable as compared to grinding wheel so they conform to the shape of the workpiece as they wear in.
To counteract their friability, honing stones may be treated with wax or sulphur to improve life, wax is more commomly used for environmental reasons.
Honing can be made with any abrasive material but the most commonly used materials are coroundum, silicon carbide, cubic boron nitride, or diamond.

Working of Electrochemical Honing:
In electrochemical honing, electrolyte like sodium chloride, sodium nitrate are used.
The workpiece used in the electrochemical machining is a cylinderical workpiece which has to be cleaned from inside using electrochemical honing process.
At first, the abrasive tool is inserted into the cylindrical workpiece.
The abrasive tool which is inserted into the workpiece rotates inside it as well as have up and down resiprocatory motion.
Electrolyte is supplied to this process inside the cylindrical workpiece using a nozzle.
In this process, the workpiece acts as anode and the tool acts as cathode. In this process, a constant DC current is supplied.
The metal part of the tool apart from the stone is conductive, this metal part reacts with the electrolyte.
Due to the reaction, material starts removing from the internal part of the workpiece and a surface finish is obtained in the inside surface of the cylindrical workpiece.
The final finsih is given by the abrasive tool or the honing stone.
As the abrassive tool is an insulator so it will be only used in rubbing.
The final finish provided by the abrasive tool is very neat and of high quality.

Following are the main specifications of Electrochemical Honing Process:
i) The pressure during the entire honing pressure is kept approx. 1000 kPa.
ii) A contant DC current is used in this process with a current density of nearly 465 Amperse per square meters.
iii) The temperature of the electrolyte used is kept nearly 40 degree Celsius.
iv) A voltage of 6 to 30 volts is used in this process.
v) In this process, a tolerance of around 0.003 mm is obtained.

Advantages of Electrochemical Honing:-

1 In this process, no heat is produced.
2 Another advantage is that we do not have to do the shaping process after the electrochemical honing process as both surface finish and shaping is done in the same process.
3 For hard materials, traditional process of machining are not applicable but by using electrochemical honing hard or tough material can also be machined.
4 Very low tolerance is obtained in this process.
5 This process also results in deburring and no stress is developed as a result of this process.

Disadvantages of Electrochemical Honing:-

1 The cost of the eqipments used in this process is high.
2 It is only applicable to hard materials.
3 This process can be carried out by skilled labour only.

Applications :

1 ECH is widely used in power generation amd powerchemical industries.
2 It is used in gear teeth error correction.
3 It is used in increasing life span of the roller , gears, sleeves, dies, gears and internal cylinders.
4 It is also used in processing different materials like carbide, titanium, alloys, Inconel Incoloy, Titanium alloys, etc.