Electrical Discharge

Machining – Die Sinking

Presented and

Arranged by:

Khairu bin Kamarudin

Introduction

EDM - Electrical Discharge Machining

Process to remove metal through the action of an electrical discharge of short duration and high current density between the tool and the workpiece.

Introduction

DIE SINK WIRE CUT

Principles of EDM–DIE SINK

Equipment of EDM

Electrode Dielectric system

Power supply

Servo system

Principles of EDM

Electric spark is used to cut (erode) the

workpiece, which takes a shape opposite to

that of the cutting tool or electrode.

The electrode and the workpiece are both

submerged in a dielectric fluid

A servo mechanism maintains a gap

A direct current is delivered to the electrode

These electrical energy impulses vaporize

the oil

Principles of EDM (cont..)

Permits the spark to jump the gap

Intense heat is created in the localized area

of the spark impact

The metal melts and a small particle of

molten metal is expelled from the surface of

the workpiece.

The dielectric fluid carries away the eroded

particles

Basic process

1. An arc jumps between two points

along the path of least resistance.

Basic Process 2. The energy of the arc is so

concentrated that it causes the

electrode and the work to melt. But the

electrode materials is chosen so that it

melts less

3. The metal and dielectric fluid are

partly vaporized causing sudden

expansion.

4. The blast from the expanding vapors

knocks some molten particles loose and

the remaining molten metal hardens.

Process Phase Animation

Electrode The electrode in die sinking EDM is formed to the

shape of the cavity desired

Common electrode materials are graphite, copper,

copper graphite, copper tungsten, brass, and steel.

Electrode materials, therefore must have the

following characteristics:

Easily machinable

Be good conductors of electricity and heat.

Provide good surface finishes on the

workpiece Resist deformation during the erosion

process

Exhibit low electrode(tool) wear rates

Electrode (cont…)

Electrode Material

Stainless steel

Titanium

Cast iron

Steel

Silver

Gold

Copper

Brass

Zamac

Aluminum

Hastelloy

Kovar

Carbide

Inconel

Hard tool steels

Iron

Molybdenum

Chromium

Cobalt

Manganese

Zirconium

Tungsten

Tantalum

Niobium

Electrode

Power supply

Transforms the AC into the pulsed direct current

(DC) to produce the spark discharges at the

machining gap Time-control function that control the length of time

that current flows each pulse

Controls the amount of current allowed to flow

during each pulse (measured in microseconds)

Power supply (cont…)

Phase 1 - Formation of a high-conductivity bridge across the gap

Phase 2 - voltage increase

- formation of a spark channel between the two surfaces

Phase 3 - voltage decrease, current increase

- material melts and vaporizes, a bubble rapidly expands outward

Phase 4 - electrical pulse is terminated, the spark stopped

- explosive expulsion of molten metal, formation of

a small crater in both surfaces

- dielectric fluid remove solidified balls of material

and gas bubbles

Servo System

Automatically maintains a constant gap

between the electrode and the workpiece React by reversing and feeding direction

controlled by the power supply

If the gap is too large, ionization of the dielectric fluid does not occur and machining cannot take place

If the gap is too small, the tool and workpiece may weld together.

Dielectric System

Three functions are performed by the dielectric fluids

a. Insulator between the electrode and the

workpiece

b. Coolant to draw away the small amount of heat

generated by the sparks

c. Flushing medium to remove the metal by-

products from the cutting gap

Dielectric System (Flushing)

Jet flushing

• The use of nozzles direct at the

cutting gap

• The least desirable flushing

method

• Reduction in flushing

effectiveness and material

removal rates

Pressure through workpiece

• The dielectric fluid is forced to

be circulated up through the

workpiece

• Limited to through-hole cutting

applications and to cavities

having holes for core or ejector

pins

Dielectric System (Flushing)-cont’

Pressure through electrode

• A hole is drilled through the

electrode

• Dielectric fluid is forced down

through the gap

• Problem when machining cavities

and holes

Dielectric System (Flushing)-cont’

Suction through electrode and workpiece

• Also known as vacuum flow

• Negative pressure (vacuum) is created

in the gap, the dielectric fluid flow through the gap

• The flow can be either up through a hole in the

electrode

• Or down through a hole in the workpiece

Dielectric System (Flushing)-cont’

EDM Process Parameters

For fast metal removal

(roughing cuts),

high amperage

low frequency

high capacitance

minimum gap

voltage

For slow metal removal

(finish cut),

low amperage

high frequency

low capacitance

highest gap voltage

EDM Process Parameters

Increasing the current For fast metal removal, high amounts of current should be

delivered to melt the maximum amount of metal

Produces larger craters in the workpiece, rough surface

finish

Use smaller charges to obtain smaller craters and finer

surface finishes,

1

2

0 250

1

0 250

Peak

curre

nt

1

2

3

4

0 250

Time in

microsec.

Pulse energy

EDM Process Parameters

Increasing spark frequency

Results in a decrease in surface roughness

Energy available for material removal during a

given period is shared by a larger numbers of

sparks

Hence the corresponding crater size is reduced

1 Volume

1 Unit

1 Volume

2 Units

1 Volume

3 Units

1 Volume

25 Units

10 Ampere

EDM Process Parameters

Overcut

Overcut is the amount the cavity in the workpiece is cut

larger than the size of the electrode.

Dependent on the amount of gap voltage

Overcut distance increases with the increased gap voltage

The amount is predictable, determined by the workpiece,

electrode material, and the operating parameters

Electrode

Workpiece

Overcut

EDM Process Parameters

Tool Wear

During the discharge process, the electrode

(tool), as well as the workpiece, is subject to

wear or erosion

Electrodes wear the fastest at sharp corners

and edges

Use as many as five electrodes to produce a

cavity

Stepped electrodes produce roughing and

finishing cuts in one pass.

Allowances, wear ratio is comparison

between the volume of workpiece material

removed versus the volume of electrode

material worn

Material Removal Rate Depends on the amount of energy in each spark

and the number of sparks produced per second.

Rate of metal removal depend on ;

Electrode material – graphit haigher material

removal rates than other electrode.

Workpiece material; more harder material, more

slower material removal rate.

Amount of current in each discharge; higher

current, removes faster

Frequency; more sparks in one second, more

material removed

Dielectric flushing condition ; good flushing will

increase the material removal rate

VIDEOS

EDM DIESINK PHASE

VIDEO 1

VIDEO 2

THANK YOU FOR

YOUR ATTENTION