1 Electrochemical Machining (ECM)- SBP

Preamble

• High cost of conventional machine tool

• Requirement of high machining accuracy and

repeatability

• Machining of hard metals

• Need of finishing operations

• Difficulty in producing intricate shapes

• Machining without tool

• Noncontact machining

Electrochemical Machining

(ECM)

Dr S B Patil

Associate Professor Mechanical Engineering

College of Engineering, Pune 411005

[email protected]

You should know

1. Explain the principle of operation of ECM.

2. Explain the process electrolysis as the basis of for the

ECM process.

3. Explain Farady’s laws of electrolysis.

4. What are the various subsystems of ECM? Explain in

brief.

You should know

5. State the various process parameters of ECM and

describe their effect

6. State the various advantages, disadvantages and

applications of ECM process. Also state the

advantages of ECM over EDM process.

7. State the various safety precautions required during

ECM process.

8. Identify the various process which uses ECM principle

and describe any one of them.

Non conventional processes (Electro-chemical

energy)

Energy type Electro-chemical energy

Basic mechanism Ion displacement

Source of immediate

energy

High current

Transfer energy

medium

electrolyte

Examples Electrochemical grinding

(ECG), electrochemical

machining (ECM)


• Uses an electrolyte and electrical current to ionize and remove metal atoms

• Can machine complex cavities in high-strength materials

• Leaves a burr-free surface

• Not affected by the strength, hardness or toughness of the material



Operating Principle-ECM

• As the tool approaches

the work piece it erodes

the negative shape of it.

Thus complex shapes are

made from soft copper

metal and used to

produce negative

duplicates of it. This

process is called

electrochemical sinking


• The tool may also be connected to a CNC machine to

produce even more complex shapes with a single tool.


• Several tools may be joined to provide a fast broaching

technique on hardened material.

• Conventional machines may be easily changed to an

ECM and is a common practice.

ECM Process parameters

1. Material- Type and composition

2. Electrical parameters- voltage, current

3. Electrolyte- type, temperature, pressure

4. Operating parameters- gap, feed

ECM-Main Subsystems

• The power supply.

• The electrolyte circulation system.

• The control system.

• The machine.

ECM Components

(Power)

• The power needed to operate the ECM is obviouslyelectrical. There are many specifications to this power.

• The current density must be high.

• The gap between the tool and the work piece must below for higher accuracy, thus the voltage must be low toavoid a short circuit.

• The control system uses some of this electrical power.

Commonly used electrolytes

• Sodium chloride

• Sodium chromate

• Sodium hydroxide

• Potassium nitrate

• Sodium sulphate

• Potassium chloride

• Sodium fluoride

ECM Components

(electrolyte circulation system)

• The electrolyte must be injected in the gap at high speed

(between 1500 to 3000 ml/min).

• The inlet pressure must be between 0.15-3 MPa.

• The electrolyte system must include a fairly strong pump.

• System also includes a filter, sludge removal system,

and treatment units.

• The electrolyte is stored in a tank.

ECM Components

(control system)

• Control parameters include:

– Voltage

– Inlet and outlet pressure of electrolyte

– Temperature of electrolyte.

• The current is dependant on the above parameters and

the feed rate.

ECM Components

(Machine)

• The machine is a major subsystem of the ECM.

• It includes the table, the frame, work enclosure (prevents

the electrolyte from spilling), the work head (where the

tool is mounted)

• The tools (electrodes) are also part of the machine

system

ECM-Advantages

• There is no cutting forces therefore clamping is not

required except for controlled motion of the work piece.

• There is no heat affected zone.

• Very accurate.

• Relatively fast

• Can machine harder metals than the tool.

Advantages over EDM

• Faster than EDM

• No tool wear at all.

• No heat affected zone.

• Better finish and accuracy.

ECM-Disadvantages

• More expensive than conventional machining.

• Need more area for installation.

• Electrolytes may destroy the equipment.

• Not environmentally friendly (sludge and other waste)

• High energy consumption.

• Material has to be electrically conductive.

ECM-Applications

• The most common application of ECM is high accuracy duplication. Because there is no tool wear, it can be used repeatedly with a high degree of accuracy.

• It is also used to make cavities and holes in various products.

• Sinking operations (RAM ECM) are also used as an alternative to RAM EDM.

• It is commonly used on thin walled, easily deformable and brittle material because they would probably develop cracks with conventional machining.

ECM-Economics

• The process is economical when a large number of

complex identical products need to be made (at least 50

units)

• Several tools could be connected to a cassette to make

many cavities simultaneously. (i.e. cylinder cavities in

engines)

• Large cavities are more economical on ECM and can be

processed in 1/10 the time of EDM.

ECM-Products

• The two most common products of ECM are turbine/compressor blades and rifle barrels. Each of those parts require machining of extremely hard metals with certain mechanical specifications that would be really difficult to perform on conventional machines.

• Some of these mechanical characteristics achieved by ECM are:– Stress free grooves.

– Any groove geometry.

– Any conductive metal can be machined.

– Repeatable accuracy of 0.0005”.

– High surface finish.

– Fast cycle time.

Safety Considerations

• Several sensors are used to control short circuit,turbulence, passivation, contact and over currentsensors. In case of contact, immense heat would begenerated melting the tool, evaporating the electrolyteand cause a fire.

• The worker must be insulated to prevent electrocution.

• The tool and the work piece must be grounded beforeany handling is performed.

Safety Consideration

• Hydrogen gas emitted is very flammable, so it should be disposed of properly and fire precautions should be taken.

• The waste material is very dangerous andenvironmentally unfriendly (metal sludge) so it must berecycle or disposed of properly.

• Electrolyte is highly pressurized and worker must check for minor cracks in piping before operating.

Pulsed Electrochemical Machining

• A form of electrochemical machining; the current is

pulsed to eliminate the need for high electrolyte flow

• Improves fatigue life of the part

Electrochemical Grinding

• Uses a rotating cathode embedded with abrasive

particles for applications comparable to milling, grinding

and sawing

• Most of the metal removal is done by the electrolyte,

resulting in very low tool wear

• Adaptable for honing

Electrochemical Grinding

Documents

1 Electrochemical Machining (ECM)- SBP