Electric Discharge Hybrid-Machining Processes

Fundamentals and Applications

Basil Kuriachen, Jose Mathew, Uday Dixit, Basil Kuriachen, Jose Mathew, Uday Dixit, Uday Shanker Dixit, Basil Kuriachen, Jose Mathew, Uday Shanker Dixit

• Publisher: CRC Press
• Year: 2022
• Print ISBN:
  9781032064321
• eBook ISBN:
  9781000517828
• Topic: Tecnologia e ingegneria
• Subtopic: Meccanica

This book provides the knowledge and insight into the fundamental aspects of Electric Discharge Machining (EDM) processes and various hybrid machining technologies derived to improve the machining efficiencies. Fundamental theory of material removal, recent research trends and future research directions have been covered in each chapter. After explaining EDM, Dry and Near-dry EDM processes, Electrochemical Spark Machining, Arc Machining processes, Electric Discharge Hybrid-Turning processes, Electrical Discharge Grinding, Electric Discharge Milling, and various assisted EDM processes have been discussed. Finally, modeling and simulation of hybrid machining processes are also included.

• The book reflects the recent developments and trends in electric discharge hybrid machining processes.
• It covers in detail the basics of EDM, various hybrid and assistive technologies in EDM.
• It includes the updated discussion on the significance of process parameters in various hybrid EDM processes.
• An overview of modelling and simulation of hybrid EDM process is provided.

This book is aimed at Graduate students, researchers in manufacturing engineering, production engineering, and materials engineering.

1Electrical Discharge Machining (EDM)

Basil Kuriachen

Advanced Manufacturing Centre, Department of Mechanical Engineering, National Institute of Technology, Calicut, Kerala, India, and National Institute of Technology, Mizoram, Aizawl, Mizoram, India

DOI: 10.1201/9781003202301-1

Contents

1. 1.1Introduction
2. 1.2History of EDM
3. 1.3Working Principle
4. 1.4Pulse Generators
5. 1.5EDM Process Parameters
6. 1.5.1Electrical Parameters
7. 1.5.2Non-Electrical Parameters
8. 1.6Surface Integrity of the Machined Surface
9. 1.7Advantages and Disadvantages
10. 1.8Conclusion

1.1 Introduction

Electric discharge machining (EDM) is a modern machining process that has become a well-established alternative for machining advanced materials throughout the world regardless of each country’s level of academic or industrial advancement. Several research projects in EDM improved its machining capabilities and extended its application from working with only metallic materials to being able to work with non-conducting materials. These research projects have also developed the hybrid electric discharge machining process. At present, there are many variants of the hybrid electric discharge machining process in addition to Wire EDM, Die Sinking EDM, and Micro EDM, and so on. This chapter provides an elementary introduction to the history, material removal mechanism, essential process parameters, and the influences of the major process parameters, by considering all of the available EDM processes.

1.2 History of EDM

The first recorded attempt to use electrical energy to remove material, a ‘disintegrator’, was reported by Matulaitis and Harding in 1930 [1]. Later, during World War II, physicists B. R. and N. I. Lazarenko in Moscow observed the effect of metal removal in electric circuit breakers and maximized it for the purpose of metal machining [1]–[3]. In the early years of development, relaxation type generators, in other words, charging condensers, were used to store the discharge energy. In 1960, semiconductor switched static pulse generators achieved a duty cycle of up to 99% and increased the material removal rate [4]. With the invention of computer numerical control in the 1980s, maintaining the constant spark gap between the electrodes provided more stable sparks.

In due course, an electronic servo control system was introduced to the EDM machines, which automatically provided the required spark gap [5]. Since then, the improvement of EDM has greatly benefited the manufacturing industry, aiding in the processing of difficult-to-machine materials and it has generated specific research areas. At the same time, electrical discharge machining drew the attention of the research community who were interested in improving its process efficiency by developing a number of different variants, including WEDM, EDM drilling, EDM milling, µEDM, and the like. However, the unique nature of material removal through melting and vaporization and the problems arising around the small inter-electrode gap make the process more complex. In addition, the discharge phenomena occur for a small time interval, of the order of microseconds, making it more complicated. Therefore, both theoretical and experimental investigations of the electric spark in particular, and electrical discharge machining in general, are extremely difficult.

1.3 Working Principle

The basic working principle of the electrical discharge machining process is the localized melting and vaporization of electrodes through controlled electric sparks. In other words, the electrical energy is converted into thermal energy through sparks, and it is effectively utilized to remove the materials. It is a non-contact material removal process wherein no mechanical interaction between the tool and workpiece occurs. Hence, the mechanical properties of tools and work pieces haven’t got a significant role in the process. The removal of material takes place between the tool and workpiece during the pulse ‘on’ time of a pulsed DC power supply.

Figure 1.1Basic schematic diagram of EDM.

A basic scheme of the EDM process is shown in Figure 1.1. The electrodes are connected to a pulsed DC power supply, and a suitable inter-electrode gap (IEG) is maintained between tool and workpiece inside a dielectric fluid. Once the appropriate power supply is established between the electrodes, the cold emission of electrons (also known as ‘field emission’) starts from the cathode surface due to the strong electric field. The cold emission of electrons begins where the local distance between the tool and workpiece is the narrowest due to the roughness in the bottom surface of the tool and top surface of the workpiece (Figure 1.1). For example, point A has the smaller distance between the tool and workpiece compared to point B in Figure 1.1. In the absence of an electric field, the electrons need to acquire a minimum energy level to escape from the surface of the electrodes, which is referred to as the work function. However, under the influence of an electric field, the work function required to release the electrons is reduced, and electrons start to be emitted from the cathode surface due to the cold emission. These liberated electrons are accelerated towards the surface of the anode. Once the electrons acquire enough velocity, they strike the molecules of the dielectric fluid present in the inter-electrode gap (IEG), in other words, the gap between two electrodes. Accelerated electrons divide the dielectric molecules into ions and electrons. Electrons produced in this way are referred to as ‘secondary electrons’. These electrons and ions accelerate towards the workpiece- (+) and tool-electrode (–) surfaces, respectively, within the IEG. The process repeats in the IEG and an avalanche of electrons and ions forms there. In this way, a plasma channel of very high conductivity is established between the electrodes, as shown in Figure 1.2. These electrons strike the anode surface with very high kinetic energy, thus an large amount of heat is produced locally on the anode surface. It is also understood that out of the total heat generated, two-thirds is at the anode surface and one-third is at the cathode surface. This is due to the difference in the kinetic energies of the ions and the electrons. The mass of electrons is comparatively less than that of the ions but their velocities are higher, therefore the discharge energy of the electron stream is higher.

Upon analysis, researchers [6] found that the temperature generated was in the range of 8,000–12,000 ℃. The heat is conducted into the workpiece and tool followed by melting, and vaporization. At the end of the spark, the plasma channel disappears, and the dielectric fluid present, gushes back into the space previously occupied by the plasma channel. Hence, the dielectric removes the melted portion of the electrodes in the form of debris that is semi-spherical in shape...

Table of contents

• Cover
• Half-Title Page
• Title Page
• Copyright Page
• Contents
• Preface
• Editors
• List of Contributors
• 1 Electrical Discharge Machining (EDM)
• 2 Dry and Near-Dry Electrical Discharge Machining
• 3 Electrochemical Spark Machining Process
• 4 Sequential EDM and ECM Process
• 5 Recent Trends in Arc Machining Processes
• 6 Electric Discharge Hybrid-Turning Processes
• 7 Electric Discharge Grinding (EDG)
• 8 Electric Discharge Assisted Milling
• 9 Vibration-Assisted EDM and Micro-EDM Processes
• 10 Magnetic Field Assistance in the EDM Process
• 11 Sequential Laser and Electrical Discharge Machining
• 12 Powder Mixed Electrical Discharge Machining (PMEDM)
• 13 Hybrid Micro-EDM
• 14 Modeling and Optimization of EDM-Based Hybrid Machining Processes
• 15 Application of EDM-Based Hybrid and Sequential Processes in Micro Manufacturing
• Index