1

Electrochemical Electrochemical Machining Machining

(ECM)(ECM)

2

Electrochemical Electrochemical MachiningMachiningNontraditional Nontraditional

machining process machining process of removing metal of removing metal from extremely hard from extremely hard materials using a materials using a high current high current between the between the electrolyte (tool electrolyte (tool piece) and work piece) and work piece. piece.

3

Electrochemical Electrochemical MachiningMachiningUses an electrolyte and electrical current Uses an electrolyte and electrical current

to ionize and remove metal atomsto ionize and remove metal atoms

Can machine complex cavities in high-Can machine complex cavities in high-strength materialsstrength materials

Leaves a burr-free surfaceLeaves a burr-free surface

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

4

Electrochemical Electrochemical MachiningMachining

5

Operating PrincipleOperating Principle In the actual process, the In the actual process, the

cathode is tool-shaped, more cathode is tool-shaped, more or less like the mirror image or less like the mirror image of the finished work piece. of the finished work piece.

The electrolysis process that The electrolysis process that takes place at the cathode takes place at the cathode liberates hydroxyl ions liberates hydroxyl ions (negatively charged) and (negatively charged) and free hydrogen. The hydroxyl free hydrogen. The hydroxyl ions combine with the metal ions combine with the metal ions of the anode to form ions of the anode to form insoluble metal hydroxides insoluble metal hydroxides and the material is thus and the material is thus removed from the anode. & removed from the anode. & this process continuesthis process continues

6

Operating PrincipleOperating Principle

A constant gap between Tool & work A constant gap between Tool & work Piece is maintained with Constant Piece is maintained with Constant Tool Feed Rate.Tool Feed Rate.

Conventional machines may be Conventional machines may be easily changed to an ECM and is a easily changed to an ECM and is a common practice.common practice.

7

Operating PrincipleOperating Principle The tool may also be connected to a CNC machine The tool may also be connected to a CNC machine

to produce even more complex shapes with a single to produce even more complex shapes with a single tool.tool.

8

Main SubsystemsMain Subsystems

The power supply.The power supply. The electrolyte circulation system.The electrolyte circulation system. The control system.The control system. The machine.The machine.

9

ECM Components ECM Components (Power)(Power)

The power needed to operate the ECM is The power needed to operate the ECM is obviously electrical.obviously electrical.

The current density must be high.The current density must be high. The gap between the tool and the work The gap between the tool and the work

piece must be low for higher accuracy.piece must be low for higher accuracy. The voltage must below to avoid a short The voltage must below to avoid a short

circuit. circuit. The electric current is of the order of 50 to The electric current is of the order of 50 to

40000 Ampere at 5 to 30 V D.C. for a 40000 Ampere at 5 to 30 V D.C. for a current density of 20 to 300 Ampere/Square current density of 20 to 300 Ampere/Square cm, across a gap of 0.05 to 0.70 mm cm, across a gap of 0.05 to 0.70 mm between the tool and the work piece.between the tool and the work piece.

10

ECM Components ECM Components (electrolyte circulation (electrolyte circulation

system)system) The electrolyte must be injected in the gap at The electrolyte must be injected in the gap at

high speed (between 1500 to 3000 m/min).high speed (between 1500 to 3000 m/min). The inlet pressure must be between 0.15-3 MPa.The inlet pressure must be between 0.15-3 MPa. The electrolyte system must include a fairly The electrolyte system must include a fairly

strong pump with stored tank.strong pump with stored tank. System also includes a filter, sludge removal System also includes a filter, sludge removal

system, and treatment units. system, and treatment units. The electrolyte should posses good electrical The electrolyte should posses good electrical

conductivity, non-toxicity, chemical stability, non-conductivity, non-toxicity, chemical stability, non-corrosive property, low viscosity, and high corrosive property, low viscosity, and high specific heat. specific heat.

Common electrolytes are NaCl, sodium nitrate, Common electrolytes are NaCl, sodium nitrate, potassium chloride, NaOH, sodium fluoride, potassium chloride, NaOH, sodium fluoride, sulfuric acid, and sodium chlorate. sulfuric acid, and sodium chlorate.

11

ECM Components ECM Components (control system)(control system)

Control parameters include:Control parameters include: VoltageVoltage Inlet and outlet pressure of electrolyteInlet and outlet pressure of electrolyte Temperature of electrolyte. Temperature of electrolyte.

The current is dependant on the The current is dependant on the above parameters and the feed rate. above parameters and the feed rate.

12

ECM Components ECM Components (Machine)(Machine)

The machine is a major subsystem of the ECM.The machine is a major subsystem of the ECM. It includes the table, the frame, work enclosure It includes the table, the frame, work enclosure

(prevents the electrolyte from spilling), the work (prevents the electrolyte from spilling), the work head (where the tool is mounted)head (where the tool is mounted)

The tools (electrodes) are also part of the machine The tools (electrodes) are also part of the machine & should be & should be A good conductor of electricity. A good conductor of electricity. Rigid enough to take up the load due to fluid pressure. Rigid enough to take up the load due to fluid pressure. Chemically inert to the electrolyte. Chemically inert to the electrolyte. Easily machinable to make it in the desired shape.Easily machinable to make it in the desired shape.

Cu, Brass, Titanium, Copper-Tungsten, and Cu, Brass, Titanium, Copper-Tungsten, and Stainless steels are commonly used electrode Stainless steels are commonly used electrode when the electrolyte is of sodium or potassium. when the electrolyte is of sodium or potassium. Other materials are Al, graphite, bronze, platinum, Other materials are Al, graphite, bronze, platinum, and tungsten carbide. and tungsten carbide.

13

AdvantagesAdvantages

There is no cutting forces therefore There is no cutting forces therefore clamping is not required except for clamping is not required except for controlled motion of the work piece.controlled motion of the work piece.

There is no heat affected zone.There is no heat affected zone. Very accurate.Very accurate. Relatively fastRelatively fast Can machine harder metals than the Can machine harder metals than the

tool.tool.

14

Advantages over EDMAdvantages over EDM

Faster than EDMFaster than EDM No tool wear at all.No tool wear at all. No heat affected zone.No heat affected zone. Better finish and accuracy.Better finish and accuracy.

15

DisadvantagesDisadvantages

More expensive than conventional More expensive than conventional machining.machining.

Need more area for installation.Need more area for installation. Electrolytes may destroy the equipment.Electrolytes may destroy the equipment. Not environmentally friendly (sludge and Not environmentally friendly (sludge and

other waste)other waste) High energy consumption.High energy consumption. Material has to be electrically Material has to be electrically

conductive.conductive.

16

ApplicationsApplications The most common application of ECM is high The most common application of ECM is high

accuracy duplication. Because there is no accuracy duplication. Because there is no tool wear, it can be used repeatedly with a tool wear, it can be used repeatedly with a high degree of accuracy.high degree of accuracy.

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

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

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

17

EconomicsEconomics

The process is economical when a large The process is economical when a large number of complex identical products number of complex identical products need to be made (at least 50 units)need to be made (at least 50 units)

Several tools could be connected to a Several tools could be connected to a cassette to make many cavities cassette to make many cavities simultaneously. (i.e. cylinder cavities in simultaneously. (i.e. cylinder cavities in engines)engines)

Large cavities are more economical on Large cavities are more economical on ECM and can be processed in 1/10 the ECM and can be processed in 1/10 the time of EDM.time of EDM.

18

ProductsProducts The two most common products of ECM are The two most common products of ECM are

turbine/compressor blades and rifle barrels. turbine/compressor blades and rifle barrels. Each of those parts require machining of Each of those parts require machining of extremely hard metals with certain mechanical extremely hard metals with certain mechanical specifications that would be really difficult to specifications that would be really difficult to perform on conventional machines. perform on conventional machines.

Some of these mechanical characteristics Some of these mechanical characteristics achieved by ECM are:achieved by ECM are: Stress free grooves.Stress free grooves. Any groove geometry.Any groove geometry. Any conductive metal can be machined.Any conductive metal can be machined. Repeatable accuracy of 0.0005”.Repeatable accuracy of 0.0005”. High surface finish.High surface finish. Fast cycle time.Fast cycle time.

19

Safety ConsiderationsSafety Considerations Several sensors are used to control short Several sensors are used to control short

circuit, turbulence, passivation, contact circuit, turbulence, passivation, contact and overcurrent sensors. In case of and overcurrent sensors. In case of contact, immense heat would be contact, immense heat would be generated melting the tool, evaporating generated melting the tool, evaporating the electrolyte and cause a fire. the electrolyte and cause a fire.

The worker must be insulated to prevent The worker must be insulated to prevent electrocution.electrocution.

The tool and the work piece must be The tool and the work piece must be grounded before any handling is grounded before any handling is performed. performed.

20

Safety ConsiderationSafety Consideration Hydrogen gas emitted is very Hydrogen gas emitted is very

flammable, so it should be disposed of flammable, so it should be disposed of properly and fire precautions should be properly and fire precautions should be taken.taken.

The waste material is very dangerous The waste material is very dangerous and environmentally unfriendly (metal and environmentally unfriendly (metal sludge) so it must be recycle or disposed sludge) so it must be recycle or disposed of properly. of properly.

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

Thank you studentsThank you students

21