about edm machine

7/30/2019 ABOUT EDM MACHINE

1/121 | P a g e

1.0 Electric Discharge Machining

Electric discharge machining provides an effective manufacturing technique that enables the

production of parts made of special materials with complicated geometry which is difficult to produce

by conventional machining processes. Controlling the process parameters to achieve the required

dimensional accuracy and finish placed this machining operation in a prominent position. From that

reason, electric discharge machining has found broad applications in industry. The absorbing interest

for electric discharge machines has resulted great improvements in EDM technology. Nowadays,

sophisticated electric discharge machines are available for most of machine shop applications.

Figure 1.1. Basic Elements of an EDM system

Basically Electric Discharge Machining (EDM) is a process for eroding and removing material by

transient action of electric sparks on electrically conductive materials. This process is achieved by

applying consecutive spark discharges between charged workpiece and electrode immersed in a

dielectric liquid and separated by a small gap. Usually, localized breakdown of the dielectric liquid

occurs where the local electrical field is highest. Each spark melts and even evaporates a small

amount of material from both electrode and workpiece. Part of this material is removed by the

dielectric fluid and the remaining part resolidifies rapidly on the surfaces of the electrodes. The net

result is that each discharge leaves a small crater on both workpiece and electrode. Application of


2/12

2 | P a g e

consecutive pulses with high frequencies together with the forward movement of the tool electrode

towards the workpiece, results with a form of a complementary shape of the electrode on the

workpiece.

The material removal rate, electrode wear, surface finish, dimensional accuracy, surface hardness andtexture and cracking depend on the size and morphology of the craters formed. The applied current,

voltage and pulse duration, thermal conductivity, electrical resistivity, specific heat, melting

temperature of the electrode and workpiece, size and composition of the debris in dielectric liquid can

be considered as the main physical parameters effecting to the process. Among them, applied current,

voltage and pulse duration are the parameters which can be controlled easily.

Every EDM machine has the following basic elements as shown in Figure 1.1.

(i) Spark generator

(ii) Servo system

(iii) Dielectric liquid

2.0 Mechanical structure

2.1 Spark Generator

The required energy is in the form of pulses usually in rectangular form. Recent studies has been

shown that application of pulses in the form of trapezoids resulted with a marked improvement in

cutting efficiency. The optimum pulse form is not exactly a trapezoid, but similar. [54 ]

Electrical energy in the form of shot duration impulses with a desired shape should be supplied to the

machining gap. For this purpose, spark generators are used as the source of electrical pulses in EDM.

The generators can be distinguished according to the way in which the voltage is transformed and the

pulse is controlled. The discharge may be produced in a controlled manner by natural ignition and

relaxation, or by means of a controllable semiconductor switching elements. Nowadays, sophisticated

computer aided spark generators are in use as a result of fast development in electronics industry.

These type of generators give us a better manner in controlling physical parameters.

2.2 Servo System

Both electrode and workpiece are eroded during the process, after a certain time dimensions of theelectrodes will be changed considerably. The result is increase in interelectrode gap. This will


3/12

3 | P a g e

increase the voltage required for sparking. This problem can be solved by increasing the pulse voltage

or decreasing the gap distance. The former is not feasible since most of the electrical energy is used

for overcoming breaking strength and producing plasma in dielectric liquid rather than machining, in

addition to that, the required voltage can increase to the levels that spark generator can not supply,

therefore; the interelectrode gap should be maintained constant during the process. This can be

achieved by a servo system which maintains a movement of the electrode towards the workpiece at

such a speed that the working gap, and hence, the sparking voltage remains unaltered.

2.3 Dielectric Circuit

High cooling rates during resolidification process changes the chemical composition of the both

electrodes and dielectric liquid machining particles called debris are formed. Formation of such

particles effects on machining performance, therefore, dielectric liquid should be circulated to prevent

contamination in working gap. This circulation is done by a dielectric circuit which is composed of a

pump, filter, tank and gages.

2.4 Mechanical Structure

EDM machines has similar construction with conventional drilling and milling machine frames withvertical tool feeding and horizontal worktable movements. Since there is not a real contact between

electrodes, thats why, it is considered that, the frame elements not taking much force as in

conventional machining so simpler design is possible. This consideration needs a little bit attention,

because gas bubbles collapses at the end of discharge and cause high frontal shock waves, therefore;

the frame should be strong enough to keep its dimensional stability.

3.0 Operation Types of Electric Discharge Machines

Electric discharge machining enables the machining operation in several ways. Some of these

operations are similar to conventional operations such as milling and die sinking others have its own

characteristic. Different classifications are possible and also it should be keep in mind that, current

developments in its technology adds different types of operations. But a simple and general

classification can done by considering famous applications such as ,

Die Sinking EDM


4/12

4 | P a g e

Wire EDM EDM Milling Wire Electric Discharge Grinding

4.0 History EDM Die-sinking

Die-sink EDM

Two Russian scientists, B. R. Lazarenko and N. I. Lazarenko, were tasked in 1943 to investigate ways

of preventing the erosion of tungsten electrical contacts due to sparking. They failed in this task but

found that the erosion was more precisely controlled if the electrodes were immersed in a dielectric

fluid. This led them to invent an EDM machine used for working difficult to machine materials such

as tungsten. The Lazarenkos' machine is known as an R-C-type machine after the RC circuit used to

charge the electrodes.

Simultaneously, but independently, an American team, Harold Stark, Victor Harding, and Jack

Beaver, developed an EDM machine for removing broken drills and taps from aluminium castings.

Initially constructing their machines from feeble electric-etching tools, they were not very successful.

But more powerful sparking units, combined with automatic spark repetition and fluid replacement

with an electromagnetic interrupter arrangement produced practical machines. Stark, Harding, and

Beaver's machines were able to produce 60 sparks per second. Later machines based on the Stark-

Harding-Beaver design used vacuum tube circuits that were able to produce thousands of sparks per

second, significantly increasing the speed of cutting.


5/12

5 | P a g e

5.0 Introduction of EDM Die Sinking Machine

EDM die sinking machine consists of an electrode and workpiece that are submerged in an insulating

liquid such oil or, less frequently, other dielectric fluids. The electrode and workpiece are connected

to a suitable power supply.

As the electrode approaches the workpiece, dielectric breakdown occurs in the fluid forming a plasma

channel and a small spark jumps. These sparks usually strike one at a time because it is very unlikely

that different locations in the inter-electrode space have the very identical local electrical

charachetistics which would enable a spark to occur simultaneously in all such locations.

The EDM die sinking process is most widely used by the mould-making tool and die industries, but is

becoming a common method of making prototype and production parts, especially in the aerospace,

automobile and electronics industries in which production quantities are relatively low.


6/12

6 | P a g e

6.0 Advantages of EDM Die-sinking

Complex shapes that would otherwise be difficult to produce with conventional cutting tools.

Extremely hard material to very close tolerances.

Very small work pieces where conventional cutting tools may damage the part from excess

cutting tool pressure.

There is no direct contact between tool and work piece. Therefore delicate sections and weak

materials can be machined without any distortion.

A good surface finish can be obtained.

Very fine holes can be easily drilled.

Can cut exotic materials

Cuts through hard materials

Requires little or no polishing after the process

Cuts thin or delicate material without damaging it


7/12

7 | P a g e

7.0 Disadvantages/limitation of EDM Die-sinking

The slow rate of material removal.

The additional time and cost used for creating electrodes for ram/sinker EDM.

Reproducing sharp corners on the work piece is difficult due to electrode wear.

Specific power consumption is very high.

Power consumption is high.

"Overcut" is formed.

Excessive tool wear occurs during machining.

Electrically non-conductive materials can be machined only with specific set-up of the

process.

8.0 Flushing system in EDM Die-sinking

To aid flushing and clear debris from the gap. A poor flushing point in your geometry that could

potentially cause wire breaks when using aggressive settings, a G10L10 command can be inserted to

reduce the power setting. In order to keep a stable machining process regarding aspects such as a

proper dispersion of discharges along the frontal area of the electrodes, an uniform tool electrode

wear, a good de-ionization of the dielectric and an adequate flushing of debris, so that any excessive

adhesion of particles from the work piece or dielectric by products be observed on the bottom of the

tool electrode. Short-circuits and arc-discharges as a consequence of the proper flushing of eroded

particles away from the working gap. Smaller values of duty factor (ti < to) were avoided because it

would lead to very low discharges frequency, consequently decreasing the material removal rate Vw.

On the other hand, very high levels of (ti > to) would probably cause an over-concentration of debris

in the working gap leading to non-uniform material removal rate Vw. At the end of the pulse duration,

ti an interval time, to is established in order to de-ionize the dielectric and flush away the material that

has been melted during the time the plasma channel is sustained


8/12

8 | P a g e

8.1Type of flushing :

8.1.1 Pressure flushing

Also called injection flushing, is the most common and preferred method for flushing. One

great advantage of pressure flushing is that the operator can visually see the amount of oil that

is being used for flushing. With pressure gauges, this method of flushing is simple to learn

and use.

Pressure flushing through the electrode


9/12

9 | P a g e

Pressure flushing throught the workpiece

8.1.2 Suction flushing


10/12

10 | P a g e

Suction or vacuum flushing can be used remove eroded gap particles. Suction flushing

can be done through the electrode or through the workpiece. Suction flushing minimizes

secondary discharge and wall tapering. Suction flushing sucks oil from worktank, not

from the clean filtered oil as in pressure flushing. For suction cutting, efficient cutting is

the best accomplished when the work tank oil is clean.

Suction flushing through the electrode

suction flushing throught the workpiece


11/12

11 | P a g e

8.1.3 Jet flushing

Jet or side flushing is done by tubes or flushing nozzles which direct the dielectric fluidinto the gap, as shown in figure below.

9.0 Application and sample product of EDM in industry.

Common applications for EDM machining include creating plastic molds, die casting dies and forging

dies. It can also be used for manufacturing engine parts such as titanium alloy or nickel based super

alloy compressor blades. Prototype and production parts are more often made through EDM

machining methods, especially in the aerospace and electronics industries because of the low

production quantities. Other industries that use EDM machining include food and beverage,automobile, stamping, extruding, defence and medical.


12/12

2 |

about edm machine

Documents