ADVANCE NON TRADITIONAL MACHINE EDM (ELECTRIC DISCHARGE MACHINE) TEORY AND APPLICATION

NON TRADITIONAL MACHINE

Type of energy	Mechanism of metal removal	Transfer media	Energy source	Process
Mechanical	Erosion	High velocity particles	Pneumatic / hydraulic pressure	AJM, USM, WJM
	Shear	Physical contact	Cutting tool	Conventional machining
Electrochemical	Ion Displacement	Electrolyte	High current	ECM, ECG
Chemical	Ablative relation	Reactive environment	Corrosive agent	CHM
Thermoelectric	Fusion	Hot gases	Ionized material	IBM, PAM
		Electrons	High voltage	EDM
	Vapourization	Radiation	Amplified light	LBM
		Ion strean	Ionized material	PAM

AJM	Abrasive Jet Machining	IBM	Ion Beam Machining
CHM	Chemical Machining	LBM	Laser Beam Machining
ECG	Electrochemical Grinding	PAM	Plasma Arc Machining
ECM	Electrochemical Machining	USM	Ultrasonic Machining
EDM	Electric Discharge Machining	WJM	Water Jet Machining

Products made by EDM

Electrical Discharge Machining, more commonly known as EDM or spark machining, removes electrically conductive material by means of rapid, repetitive spark discharges from electric pulse generators with the dielectric flowing between the tool and the workpiece.

No physical cutting forces exist between the workpiece and tool.

Unjuk kerja EDM

Unjuk Kerja proses EDM (Electric Discharge Machining) sangat tergantung pada parameter pemesinan yang digunakan, seperti tegangan, arus, arc on dan arc off time, spark gap, cairan dielektrik.

Kualitas berkaitan dengan kekasaran permukaan.

Kuantitas berhubungan dengan laju pembuangan beram atau metal removal rate.

Process Advantages:

•Sparks occur in random directions over smallest gap. It makes possible to create or reproduce almost any conceiveable geometri, even undercuts.

•The erosion unit must feature a device for controlling the machining gap. The process is always automatic and does not need large process force.

• Electrical discharges are spatially very limited.

•The electrical discharges are not affected by the machining geometry and permit simultaneous production of large mold batches.

• There are not restriction on the choice of material for the tool electrode.

Design Advantages :

• Hardened as well as naturally hard materials can be machined freely.

• Tools with complex geometries present no particular problem

•There are fewer individual design parts and no split, bolted connections or joined  parts resulting in more compact molds

 

Production Advantages :

• Close production tolerances and faithful reproduction are obtained

• Automatic machine operation, electronic process easily monitored

• Preparation can generally be made at the same time as for other prepared work

•Less machining time  is required because there are fewer machining operations, making day/night operation possible

EDM Constrain

1. EDM performance is affected  mostly by the process parameter values (on-time, current, off-time, etc.), and thus their values are set according to the desirable performance

2. Also, the material of the electrode must have suitable properties to decrease the electrode wear rate and increase the part MRR.

  4. The electrode material must have acceptable mechanical strength and melting point to  reduce tool wear and edge weakness.

5. The dimensional accuracy of the produced part depends on the dimensional accuracy and the surface texture of the electrode.

   6. Shape details and recesses affect the electrode performance

 

Functions and Properties of Dielectric Fluids

 

 1.Remain electrically non conductive until the required breakdown voltage is reached (ie. should have high dielectric strength).

 2.Breakdown electrically in the shortest possible time once the breakdown voltage reached.

    3.Provide an effective cooling medium.

 4.Carrying away the swarf particles (materials, decomposition products, hydrogen, carbon, bubbles). 

Viscosity

ASTM D445-82

A higher viscosity valueindicates the fluid is more “viscous”, and flows more slowly than a lower viscosity fluid. The warmer the fluid becomes, the thinner, or lower viscosity.

Viscosity is most commonly measured in Centistokes (cSt) @ 40°C.

Viscosity is an important factor when considering an EDM fluid, since the lower the viscosity, the easier the fluid is to pump and the better its flushing characteristics.

Copper Impregnated Graphite

Copper is one of the world’s more conductive materials. Copper graphite is easy to machine with even the most complex details. The presence of copper in the open porosity lowers the electrical resistivity of the electrode, maximizing the flow of energy into the workpiece and increasing the metal removal rate.

Thermal Conductivity and Melting Temperature

Some metals—such as copper and copper alloys—have a low melting point, but are such good thermal conductors that the spark energy is so quickly dissipated throughout the workpiece that very little remains in the EDM cut.

Some other metals—such as tungsten carbide—have higher melting points and lower thermal conductivity. The issue here is that higher temperatures are needed to maintain efficient metal removal; however, these higher temperatures run the risk of damage to the workpiece.

 

Rapid tooling electrodes

Electrodes manufactured using RP techniques:

1.  high dimensional accuracy

2.  appropriate surface roughness

3.  EDM applications (roughing, semi-roughing, and finishing) is necessary

4.  According to the material electric properties (non-conductive, conductive, pattern for casting)

5.  Quality characteristics (dimensional accuracy, surface roughness).

The effects of the EDM process on tool steels

The surface of the steel is subjected to very high temperatures, causing the steel to melt or vaporize The effect upon the steel surface has been studied to ensure that the tool maker may enjoy the many benefits of the EDM process, while producing a tool that will have a satisfactory production life.