The word machining means removal of any substance and the word electrochemical resembles the mode of energy used. The two terms combined together give rise to a process known as electrochemical machining. In this article, we are going to see all the related concept on Electrochemical Machining (ECM).
What is Electrochemical Machining?
Electrochemical machining is a process of removing metal with the help of the electrolysis process. The electrochemical process is also known as the reverse of the electroplating process because, in electroplating, the metal is deposited on the surface of the workpiece, while in electrochemical machining the metal is removed from the workpiece. This process is used for the large-scale production of machined parts.
History of Electrochemical Machining
Electrochemical machining is a modified yet different process which has its roots connected to electrolytic polishing, which was founded in the year 1911 by a Russian chemist E. Shpitalsky.
It was in the year 1929 ECM was experimentally developed by W. Gussef.
It was in 1959 when an engineering company commercialised the used of electrolysis for removal of metals. The ECM technology kept on becoming better with their passage of time passed .
Principle of Electrochemical Machining
The Electrochemical machining process is based on Faraday’s law of electrolysis.
Faraday’s law of electrolysis:
It states that when two electrodes, anode ( +ve) and cathode (-ve) are placed in an electrolyte the mass of the metal deposited on the cathode coming from the anode is directly proportional to the potential difference applied across the electrodes.
Conceptual Electrochemical Model
In the setup shown below, NaCl is used as an electrolyte, the workpiece is placed as the anode, tool (desired shape) is used as cathode and a potential difference is applied. There is a very small gap between the workpiece and the tool for the removal of material.
As soon as a potential difference is applied between the anode and the cathode, the ions start moving from anode to cathode.. The negative ions are attracted towards the workpiece which is placed at the +ve potential and positive ions are attracted towards the tool which is placed at the – ve potential. The chemical reactions taking place in the basic process of electrochemical machining are as follows:
2H+ + 2e– = H2
Hydrogen ions gain electrons and get converted into hydrogen gas. (at cathode)
Fe = Fe++ + 2e–
The iron atom releases its 2 electrons and gets converted into Iron ions. (at the anode)
Na++OH– = NaOH
Fe2++2Cl– = FeCl2
Sodium ions react with hydroxyl ions to form Sodium hydroxide.
Iron ions react reacts with chlorine ions to form iron chloride (slug)
Construction of Electrochemical Machining Setup
An electrochemical plant has various parts, those are as follows,
#1 Power supply
The power supply is the source of energy that is provided to the setup. The power supply is generally a DC battery consisting of a potential difference from 3 to 30V depending upon the requirement.
An electrolyte is a salt solution in which the workpiece and tool is kept during the process of machining. It acts as a current-carrying medium between the workpiece and the tool. It also helps in the removal of waste products from internal gaps and also acts as a coolant by preventing overheating of the tool and the workpiece. Different electrolytes used in ECM are Sodium chloride (NaCl), Sodium nitrate (NaNO3), hydrochloric acid (HCl), etc.
Tool or cathode used in ECM is one of the electrodes. It is also the desired shape in which the workpiece is to be cut. The tool used in ECM should always have accurate dimensions.
#4 Mechanical System
One of the most important elements in ECM is the mechanical system. It is used for the advancement of a tool that is perpendicular to the workpiece and is at a constant velocity.
The tank contains the electrolyte, tool, and the workpiece. All the reactions take place here.
#6 Pressure Gauge
A pressure gauge is used to measure the pressure of electrolytes which is supplied to the tool.
#7 Flow Control Valve
A flow control valve is used to control the flow of electrolyte which is supplied to the tool.
#8 Pressure Relief Valve
In case the pressure of electrolyte flow exceeds a certain limit, the pressure relief valve opens and it sends the electrolyte back to the tank.
#9 Reservoir Tank
The tank that stores pure Electrolyte is called the reservoir tank.
There are two pumps used namely A and B. Pump A is used to draw electrolyte from the reservoir tank and pump B is used to supply the electrolyte to the reservoir tank.
#11 Filter and Centrifuge
A filter is used to filter the electrolyte reaching the reservoir tank. And prevents the accumulation of excess electrolytes. The function of a centrifuge is to separate the slug from the electrolyte.
#12 Slug Container
A slug container is used to store the slug which is separated from the electrolyte. This slug can be used for various experimental purposes.
Working of Electrochemical Machining
The working of electrochemical machining starts with the advancement of the tool towards the workpiece. The tool and the workpiece are kept in a suitable electrolyte with a very small gap between them.
As soon as the potential difference is applied (DC), the workpiece starts behaving as an anode and the tool starts behaving as a cathode.
When the condition of electrolysis is fulfilled, the removal of metal from the workpiece starts. The removal takes place according to the shape of the tool. Material is removed from the workpiece and gets settled down in the form of a slug, which is due to the flow of electrolyte.
The electrolyte then goes through a filtration process. In the filtration process, the electrolyte is passed through a centrifuge where the slug is removed. Then it passes through a filter where other remaining impurities are removed. If there is an increase in the pressure of the electrolyte, the pressure valve deviates the flow of the electrolyte directly to the tank.
Applications of Electrochemical Machining
- As mentioned earlier in the article ECM is used for heavy machining of hard materials which cannot be machined using conventional methods.
- Due to its high accuracy and surface finish, ECM is used for micromachining. As there is no contact between the tool and workpiece the final product obtained is accurate at the atomic level.
- ECM is also used for the production of very small gear systems which cannot be machined using typical machining processes.
- ECM is used for machining turbine blades as it is difficult to machine due to its complex concave structure.
- ECM can also be used for drilling and milling operations.
Advantages of Electrochemical Machining
- Suitable for hard materials
The electrochemical machining process is used for machining hard materials. Those materials which are difficult to be machined using typical processes are machined by electrochemical machining.
- Negligible stresses
Unlike any other machining process, in electrochemical machining, there are no stresses produced as there is no contact between the tool and the workpiece.
- No heat produced
There is negligible heat produced in this process of machining as there is no friction involved in electrochemical machining. If a very small amount of heat is produced due to the movement of ions then this heat is absorbed by the electrolyte in which the workpiece is dipped.
- No tool wear
As there is no friction involved and no heat produced in electrochemical machining, the tool is not subjected to any stresses, resulting in no wear and tear of the tool material.
- Surface finish
The surface finish obtained in the case of electrochemical machining is excellent. Mirror finished surfaces can be obtained by this process of machining. This is due to the removal of material at an atomic level.
- Accurate dimensions
Accuracy is very important in most industries. With the help of ECM, we can obtain accurate dimensions because the electrochemical process involved in ECM works on atomic levels.
- Mass production
The electrochemical machining process is generally used for the mass production of machined parts. This is because various factors like electrolyte can be reused, no tool wear, no heat produced, etc.
Disadvantages of Electrochemical Machining
- Higher cost
The cost of electrochemical machining equipment is much higher when compared to other machining processes. The cost of maintenance is also high in the case of ECM.
Generally, the parts which are machined using ECM are metals. We know that metals are electropositive and get corroded when they come in contact with a liquid. Hence there is a chance that the metal workpiece may get corroded due to the electrolyte.
- Large area
An ECM setup consists of various individual parts. Due to so many complex working parts, an ECM setup requires a large area. Hence it is difficult to install the setup in a small area.
- Limited materials
One of the major drawbacks of ECM is that only those materials which are good conductors of electricity can be machined.
Semiconductors and bad conductors are not suitable for the machining processes through ECM.
- Hazardous to the environment
The reuse of electrolytes can be done for a limited cycle. After a certain time, there’s a need to dispose of the electrolyte and slug produced in the process. The waste products produced in the ECM process are harmful to dispose of.
- Introduction to Non-Traditional Machining [PDF] – For IIT Kanpur
- Video Lecture on Non-traditional Machining- NPTEL