Chapter 3 Electrical Discharge Machining (EDM)author.uthm.edu.my/uthm/www/content/lessons/2686/Chapter 03 (EDM... · Electrical Discharge Machining (EDM) EDM-Die Sinker EDM-Wirecut

Chapter 3

Electrical Discharge Machining (EDM)

Electrical Discharge Machining (EDM)

EDM-Die Sinker EDM-Wirecut

Chapter 3: EDM

© ASSOC. PROF. DR. MOHD AMRI LAJIS, Faculty of Mech. and Manuf. Engineering, UTHM (2012)

History The first EDM was invented bytwo Russian scientists, Dr. B.R.Lazarenko and Dr. N.I.Lazarenko at 1943 in theTechnical Institute of Moscowduring the second world war.

He introduces:

The RC (relaxation circuit) which

provided consistent dependable

control of pulse times.

Using servo control circuit in

order to find and hold a spark gap

automatically.

Introduction to EDMChapter 3: EDM


Classification of EDM processes

Elecro-Discharge Machining

(EDM)

Sinking

by EDM

Cutting by

EDMGrinding By

EDM

Slicing by

EDM using

rotary disc

Wire Cutting

by EDM

Drilling by

EDM

Die Sinking

by EDM

Slicing by

EDM using a

ribbon

External

EDM

Grinding

Internal EDM

Grinding

Form

Grinding by

EDM

Cutting

by EDM

Cutting

and

Sinking

Chapter 3: EDM


The principles operation of EDM

• EDM processes remove metal by a series of

discrete electrical discharges (sparks) that

cause localised temperatures high enough to

melt or vaporize the metal.

• The potential difference of current intensity

between tool electrode and the workpiece is

sufficiently high, a transient spark discharges

through the fluid removing a very small amount

of metal from the workpiece surface.

Chapter 3: EDM


The schematic diagram of EDM components

Chapter 3: EDM


EDM Die sinker and assembly parts Chapter 3: EDM


Main parameters of EDM(a) Electrical parameters:

Ui – machining voltage (v)

ie – peak current

td – ignition delay time (µs)

te – pulse duration (µs)

to – interval time (µs)

(b) Non-electrical parameters:

- Flushing

- Types of dielectric medium (kerosene, dielectric, etc)

Chapter 3: EDM


Pulse On – Time (te – pulse duration in µs)

The duration of time (µs) the current is allowed to flow per cycle

Material removal (MRR) is directly proportional to the amount of

energy applied during this on- time

This energy is really controlled by the peak current and the

length of the on-time

Pulse Off-Time (to – interval time in µs)

The duration of time (µs) between the sparks

This time allows the molten to solidify and to be wash out of the

arc gap

This parameter is to affect the speed and the stability of the cut

If the off-time is too short, it will cause sparks to be unstable

Main parameters of EDMChapter 3: EDM


Spark gap

The distance between the electrode and

the part during the process of EDM

Duty cycle

It is a percentage of the on-time relative to

the total cycle time

This parameter is calculated by dividing the

on-time by the total cycle time( on time +

off-time)

The result is multiplied by 100 for the

percentage of efficiency or the so called

duty cycle

Intensity

Points out the different levels of power

that can be supplied by the generator of

the EDM machine.

Spark

gap

Main parameters of EDMChapter 3: EDM

Electrodes of EDM

Function of an electrode is to transmit the electricalcharges and to erode the work piece to the desired shape.

Chapter 3: EDM


Electrodes of EDM

Common electrodes used such as brass,tungsten, copper-tungsten, silver-tungsten, copper, graphite and etc.

Copper have been used primarily inresistance capacitance circuit wherehigher voltage are employed.

Graphite commonly used in applicationto get fine surface, low cost and highmaterial removal rate.

Chapter 3: EDM


Flushing

Flushing is important because it removes eroded particle from the gap between tool and work piece while machining.

Methods:

a) Vacuum (suction) through electrode

b) Suction through work piece

c) Pressure through hole flushing (injection flushing)

d) Pressure through work piece

e) Outside flushing (fluid injection, side flushing)

Chapter 3: EDM


EDM has become an indispensable/very2 importantprocess in the modern manufacturing. It is used innumerous applications such as producing die cavities forautomotive body components, connecting rods, andvarious intricate shapes, to a high degree of accuracy.

About 80–90% of EDM work is the manufacture of tooland die sets for the production of castings, forgings,stampings, and extrusions.

Micromachining of holes, slots, texturing, and milling arealso typical applications of the process.

Applications of EDM


Applications of EDM

a) Sinking of two connecting rods with electrode.

b) Sinking of extrusion insert plate of motor anchor with single electrode.

c) Machining of embossing die.

d) Machining of forging die.

e) Sinking of injection mold insert for light alloys

Chapter 3: EDM


(a) Schematic illustration of the electrical-discharge machining process.

(b) Examples of cavities produced by the electrical-discharge machining process, using shaped electrodes. Two round parts (rear) are the set of dies for extruding the aluminum piece shown in front.

(c) A spiral cavity produced by EDM using a slowly rotating electrode, similar to a screw thread.

(a) (b) (c)

Examples of parts made by advanced Machining Processes – Electrical Discharge Machining (EDM)

Chapter 3: EDM


Stepped cavities produced with a square electrode by the EDM process. The workpiece moves in the two principal horizontal directions (x-y), and its motion is synchronized with the downward movement of the electrode to produce these cavities. Also shown is a round electrode capable of producing round or elliptical cavities.

Schematic illustration of producing an inner cavity by EDM, using a specially designed electrode with a hinged tip, which is slowly opened and rotated to produce the large cavity.

Examples of parts made by advanced Machining

Processes – Electrical Discharge Machining (EDM)

Chapter 3: EDM


EDM - Wirecut

--

--

+

+ +

++

Wire EDM is a process where theelectrode is a continuouslymoving conductive wire.

Special form of EDM uses smalldiameter wire as electrode tocut a narrow kerf in workpiece

Type of wire: copper, brass,molybdenum or tungsten.Diameter: 0.08 ~ 0.3 mm.

The dielectric is usuallydeionizer water.

Chapter 3: EDM


EDM - Wirecut Work is fed slowly past wire along

desired cutting path, like a band saw operation.

Electric spark passing from a negatively charged (-) wire electrode to a positively charged (+) work piece.

The energy of the spark brings particles of the work piece to a vaporized state, resolidify into small spheres and flushed away by the dielectric oil, leaving a small pocket eroded in the work piece.

Chapter 3: EDM


Example of a wire EDM machine

Courtesy of Edison Industrial Service Center

EDM - Wirecut

Chapter 3: EDM

Examples of application of EDM - Wirecut

Chapter 3: EDM


- Example of cores removed from a part using

wire EDM to create the cavity in a high-pressure

nozzle

- Holes were drilled in the interiors so that the

wire could be strung through

- Courtesy of Edison Industrial Service Center

Examples of application of EDM - Wirecut

Chapter 3: EDM


Advantages of EDM

It is applicable to machine metals, alloys, and carbides,irrespective of their hardness and toughness.

Because there is no mechanical contact between the tooland the WP, small workpiece can be machined.

The process is widely used to produce cavities and profilesof complex and intricate shapes accurately in extra-hardmaterials.

The process leaves no burr on the edges.

EDM electrodes can be accurately produced frommachinable materials, which have a positive impact on theaccuracy of machined holes and cavities.

Chapter 3: EDM


It cannot be used if the WP material is a bad electric or non-conductive.

On machining materials, the process produces Heat-affected-zone (HAZ), which is characterized by hairline cracks and thin, hard recast layer. The surface integrity (SI) is improved if other machining processes such as CHM, shot peening, and so on, are used subsequently to EDM. This measure is done if the product will be operating in a fatigue environment.

EDM difficult to produce sharp concerns and edges.

The process is characterized by high specific energy.

Low metal removal rate (MRR).

Disadvantages/limitations of EDM

Chapter 3: EDM


Material removal rate (MRR) in EDM Chapter 3: EDM


(a) From standard table, Tm = 1453°C for nickel

Material removal rate (MRR) in EDM

(a) MRR = KI/Tm1.23

= 664(25)/(14531.23) = 16600/7755.1 = 2.1405 mm3/s = 7,706 mm3

Chapter 3: EDM


(b) From standard table, Tm = 419.5°C for zinc

Material removal rate (MRR) in EDM

MRR = KI/Tm1.23

= 664(25)/(419.51.23)= 16600/1682.5 = 9.8663 mm3/s = 35,519 mm3

Chapter 3: EDM


Material removal rate (MRR) – 2nd option

MRR (cm3/min) = (Wb - Wa) / (ρ*t)

Chapter 3: EDM


Material removal rate (MRR) – 3rd option

MRR (mm3/min) = (L * A)/t

where;L – length or thickness or height of cutting (mm) A – area of cutting (mm2)t - machining time (min)

Chapter 3: EDM


Electrode wear rate (EWR)Chapter 3: EDM


Electrode Wear Rate (EWR) – 2nd option

EWR (cm3/min) = (Wb - Wa) / (ρ*t)

Chapter 3: EDM


Thank you

Chapter 3: EDM

Documents

Chapter 3 Electrical Discharge Machining (EDM)author.uthm.edu.my/uthm/www/content/lessons/2686/Chapter 03 (EDM... · Electrical Discharge Machining (EDM) EDM-Die Sinker EDM-Wirecut