Study of Electro Discharge Machining of Non-Conductive Ceramic On Alumina & Glass E-Book

Dr. Chandan Deep Singh

• Herausgeber: BookRix
• Kategorie: Fachliteratur
• Sprache: Englisch

Veröffentlichungsjahr: 2018

Beschreibung

Electric Discharge Machining (EDM) is very important and prominent machining process
among all the newly developed non -traditional machining techniques. This process is
extremely useful for “difficult to machine” conducting materials such as heat treated tool
steels, composites, super alloys, heat resistant steels, ceramics, carbides, etc. In this
technique i.e. in EDM, the material removal of the electrode is achieved through high
frequency sparks between the tool and the work-piece immersed into the dielectric. The
Material Removal Rate (MRR), Tool Wear Rate (TWR) and surface roughness are some of
the important performance parameter of EDM process. The objective of EDM is to get high
MRR as well as achieving reasonably good surface quality of machined component. The
machining parameters that achieve the highest MRR strongly depend on the size of the
machining surface i.e. Electrode used and work-piece surface. With upcoming worldwide
important applications of Non-Conductive ceramics machining has become an important
issue which needs to be investigated in much detail. The Alumina (Al2O3), Glass and other
advanced engineering ceramics are rapidly emerging class of engineering materials
possessing a wide range of remarkable properties i.e. high hardness, chemical stability,
very low friction, unique electrical properties and these engineering ceramics posses high
wear resistance which make them highly suitable for such engineering applications as jet
engines and other aeronautical components, tools and dies and electronic sensors.

Leseprobe

Charanjit Singh, Dr. Chandan Deep Singh

Study of Electro Discharge Machining of Non-Conductive Ceramic On Alumina & Glass

BookRix GmbH & Co. KG81371 Munich

Chapter 1

CHAPTER-1

INTRODUCTION

Description of Electro Discharge Machining (EDM)

Electrical Discharge Machining (EDM) is the process of machining electrically conductive material by using precisely controlled sparks that occurs between an electrode and a work piece in the presence of a dielectric fluid. The Electrode may be considered the cutting tool.

Electrical Discharge Machining (EDM) is non-conventional process based on removing of material through melting and evaporation. No physical cutting forces between the tool and workpiece,high precision metal removing process using thermal energy by generating a spark to erode the workpiece.The work piece must be electrically conductive which is submerged into the dielectric fluid for the better erosion. A voltage is attached to both electrodes and when the breakdown voltage of the medium is reached a plasma channel allowing for a current flow is established and a discharge takes place. On the basis of plasma channel the temperature can reach T>10000K, melting and evaporating electrode material. When the energy input is stopped the discharge ends, leading to an implosion of the plasma channel followed by a collapse of the surrounding gas bubble. The reflow of the dielectric medium flushes particles away and cools the electrodes.

Wire –Cut EDM machine uses a continuous wire as the electrode. Sparking occurs from the electrode wire-side surface to the work piece.In Die-sinking type EDM machine, it requires the electrode to be machined in the exact opposite shape as the one in the work piece.

Basic fundamental of the process is that only one spark occurs at any instant. Sparking occurs in a frequency range from 2000 to 500000 sparks per seconds causing it to appear that many sparks occurring simultaneously. The spark removes

the material from both electrode and work piece, which increases the distance between electrode and the work piece. This causes the next spark to occur at the next closest point between electrode and work piece.

.

. Fig-1.1-Schematic of EDM Process

EDM is a thermal process .i.e. the material is removed by heat. Heat is introduced by the flow of electricity between the electrode and work piece in the form of spark. Material at the closest point between both i.e. electrode and work piece, where the spark originates and terminates are heated to the point where the material vaporizes.

Now the electrode and work piece should never feel more than warm to the touch during machining ,the area where each spark occurs is very hot. The area heated by the spark is very small so the dielectric fluid quickly cools the vaporised material and the electrode and the work piece surfaces. But it is possible for metallurgical changes to occur from the spark heating the work piece surface

A dielectric material is required to maintain the sparking gap between the electrode and work piece. This dielectric material is normally fluid. Die-sinker type EDM machine usually use hydrocarbon oil, while wire-cut type EDM machine normally use deionised water.

Fig.1.2 Basic Components of EDM

Dielectric fluid used in EDM machine provides important function in the EDM process, these are:

Cooling the heated material to form the EDM chip.

Introduction

Controlling the spark-gap spacing between the electrode and workpiece.

Removing EDM chip from the sparking area.

In EDM, for efficient machining, the chip must be removed from the sparking area. Removal of this chip is accomplished by flowing dielectric fluid through the sparking gap.

Brief History of EDM :

EDM originated from the need to perform machining operations on difficult-to- machine metals. The process was developed almost simultaneously in the USSR and the USA at the beginning of World War-ll.History of EDM goes as far back as 1770, when English Chemist Joseph Priestly discovered the erosive effect of electrical discharges or sparks. The EDM process was invented by two Russian Scientist, Dr.B.R.Lazarenko and Dr.N.I.Lazarenko in 1943, known as Lazarnko circuit, has been employed over many years in power supplies for EDM machines and proved to be used in many current applications.