1. Electrochemical Machining (ECM)
Dr. Lotfi K. Gaafar
13/05/2002
AUC - MENG

2. Electrochemical Machining
13/05/2002
AUC - MENG

3. Electrochemical Machining
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
13/05/2002
AUC - MENG

4. Electrochemical Machining
13/05/2002
AUC - MENG

5. Operating Principle
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
This is basically the same concept as RAM EDM, or EDM sinking. It even has a really similar name. ECM sinking, or RAM ECM. The only difference is the way the metal is removed from the work piece.
13/05/2002
AUC - MENG

6. Operating Principle
The tool may also be connected to a CNC machine to produce even more complex shapes with a single tool.
13/05/2002
AUC - MENG

7. Operating Principle
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.
Brown. Advanced Machining Technology Handbook
13/05/2002
AUC - MENG

8. Main Subsystems The power supply. The electrolyte circulation system.
The control system.
The machine.
Brown. Advanced Machining Technology Handbook
13/05/2002
AUC - MENG

9. ECM Components (Power)
The power needed to operate the ECM is obviously electrical. There are many specifications to this power.
The current density must be high.
The gap between the tool and the work piece must be low for higher accuracy, thus the voltage must be low to avoid a short circuit.
The control system uses some of this electrical power.
The current density is the amount of current that passes per area. In ECM sinking, it is approximately the current divided by the cross sectional area of the tool.
If the gap is large the current may diverge producing a distorted replica. Thus the gap should be small so that these distortions are minimal. If the gap is really small and the voltage is high, current breakthrough may occur (spark). This spark produces a short circuit, producing immense heat, and evaporating the electrolyte ruining all the process.
Some power is needed for any control system. In most cases EC machines use electrical power for their control system because it is readily available for the rest of the process.
13/05/2002
AUC - MENG

10. ECM Components (electrolyte circulation system)
The electrolyte must be injected in the gap at high speed (between 1500 to 3000 m/min).
The inlet pressure must be between 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.
As the current increases the amount of electrolyte needed to cool, flush the sludge and inhibit the reaction increases.
13/05/2002
AUC - MENG

11. 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.
The operator does not specify the current. It is calculated from the other inputs.
The gap distance is directly related to the voltage
Brown. Advanced Machining Technology Handbook
13/05/2002
AUC - MENG

12. 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
The casing is also part of the machine. It is basically all the rest of the subsystems in the ECM.
Brown. Advanced Machining Technology Handbook
13/05/2002
AUC - MENG

13. 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.
Brown. Advanced Machining Technology Handbook
Kalpakjian. Manufacturing Engineering & Technology.
13/05/2002
AUC - MENG

14. Advantages over EDM Faster than EDM No tool wear at all.
No heat affected zone.
Better finish and accuracy.
Brown. Advanced Machining Technology Handbook
13/05/2002
AUC - MENG

15. 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.
Brown. Advanced Machining Technology Handbook
Kalpakjian. Manufacturing Engineering & Technology
13/05/2002
AUC - MENG

16. 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.
It can be used to make any shape cavity, but it more often used for larger cavities for economical reasons.
Brown. Advanced Machining Technology Handbook
13/05/2002
AUC - MENG

17. 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.
Engine cylinder cavities are made by ECM. A 6 cylinder would have 6 Cathodes connected to a cassette, such that the sinking operation would be performed once for each engine rather than 6 times.
Brown. Advanced Machining Technology Handbook
13/05/2002
AUC - MENG

18. 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 ”.
High surface finish.
Fast cycle time.
Brown. Advanced Machining Technology Handbook
13/05/2002
AUC - MENG

19. Safety Considerations
Several sensors are used to control short circuit, turbulence, passivation, contact and overcurrent sensors. In case of contact, immense heat would be generated melting the tool, evaporating the electrolyte and cause a fire.
The worker must be insulated to prevent electrocution.
The tool and the work piece must be grounded before any handling is performed.
If the worker is not insulated from the ground the electricity is going to flow through him to the ground rather than going through the electrolyte. This would create a closed circuit and electrocute the worker. In the case of insulation from the ground the loop would not be closed and the electricity would not flow through the worker.
After the power source is cut out, the work piece and the tool will store some charge. When a non insulated worker touches then this extra charge will pass through the worker to the ground causing severe damage if not death.
13/05/2002
AUC - MENG

20. 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 and environmentally unfriendly (metal sludge) so it must be recycle or disposed of properly.
Electrolyte is highly pressurized and worker must check for minor cracks in piping before operating.
A small crack or leak in the electrolyte system will increase in size exponentially when the pump is operated and could explode causing serious damage to the work area and tools and machines.
13/05/2002
AUC - MENG

21. 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
13/05/2002
AUC - MENG

22. 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
13/05/2002
AUC - MENG

23. Electrochemical Grinding
13/05/2002
AUC - MENG