Micro-electrical Discharge Machining Processes

Micro-EDM drilling becomes an important fabrication process for several different industrial applications. Micro-EDM drilling provides comparative advantages over conventional mechanical micro-drilling process owing to its capability of machining difficult-to-cut materials. This chapter provides a concise overview of micro-EDM drilling process. It presents working principle of the micro-EDM drilling as well as both operating and performance parameters along with some important applications. This chapter also covers micro-EDM drilling for difficult-to-cut materials such as steel alloys, Ti alloys and Ni alloys.

This chapter introduces a novel variant of electric discharge machining (EDM) process entitled to electrical discharge milling (ED-Milling) operation. Although the mechanism of material removal is essentially identical to that of conventional EDM process, the intricacies arise predominantly pertaining to the multiple zones involved simultaneously during the sparking phenomenon. Unlike the Ram/die-sinking EDM or ED-Drilling operations comprising merely unidirectional control of the tool electrode, the ED-Milling operation is characterized by the synchronized movement of the tool in multiple axes (generally x-, y-, and z-axis) besides the high-speed rotation about its axis. This controlled motion of the tool electrode governed by the programmed instructions similar to the computerized numerical control (CNC) of conventional milling operation makes it a prospective contender especially for fabrication of 3D micro/macro-profiles. Incorporating a comparatively simpler cylindrical or in exceptional instances rectangular/square cross-sectional tool electrode to generate a complex three-dimensional feature is the distinctive capability of this operation. The chapter comprises the basic introduction to EDM process in conjunction with ED-Milling operation, different techniques of micro-tool production as well as micro-fabrication, suitability of ED-Milling operation for a variety of sophisticated areas, analysis of tool wear and the possible applications areas of the process.

Application of micro-fabrications is immense in today’s life as many products have micro-features on it as a part of aesthetics or functionality. In this chapter, novel technique called Micro-Electro-Discharge-Slotting (MEDS) has been discussed in detail. The process can be used as an alternative in case of issues difficulties in carrying out commonly used micro-EDM process variant like micro-electro-discharge milling. Micro-Electro-Discharge-Slotting, due to its specialty in its tool actuation strategy, can reduce inaccuracies that may incur in the machined feature due to deformation of the micro-tool electrode. Further, a novel micro-electrode fabrication technique, namely foil as tool electrode (FAST) EDM, has also been discussed for cutting and dressing of micro-electrodes. The technique can be used in the absence of sophisticated micro-machining facilities to fabricate micro-electrodes with relative low mechanical distortion. To understand the parameter effects, a case study has also been discussed for both the processes.

Micro-wire-electro-discharge machining (micro-WEDM) is a widely used non-conventional micromachining process to fabricate three-dimensional (3D) complex micro-features in difficult-to-machine materials. This chapter offers a concise overview on the micro-WEDM process. A brief overview on the process mechanism, system components, parameters and variants of micro-WEDM has been provided in the chapter. In addition, some of the innovative applications and advanced research studies on the micro-WEDM have been discussed in brief. Finally, current challenges that limit the wide application of micro-WEDM in industries, as well as opportunities for future research, have been discussed at the end of the chapter.

Micro-EDM is an extensively used micromachining process to fabricate microcavities on metallic surfaces. Material erosion in micro-EDM is realized by imparting controlled sparks between electrodes submerged under the dielectric fluid. Recently, micromanufacturing is in demand and resulted in miniaturization of switches, screws, gears, shafts, and other mechanical components. High aspect ratio arrayed features are used as electrodes in micro-EDM and micro ECM processes, elements of MEMS, interface elements in biomedical devices for capturing neural signals, a source of plasma, etc. Existing micromanufacturing processes have limitations in machining of high aspect ratio arrayed features of different sections on metallic surfaces. Similarly, functional surfaces which can control friction, corrosion, wettability, and hemocompatibility are difficult to fabricate by existing micromachining processes. Reverse micro-EDM (R-MEDM) process has been originated from micro-EDM process. It reverse replicates the microcavities from electrode on workpiece. Intricate machining of features with high aspect ratio can be easily realized via R-MEDM process. Use of electrode vibration enables textured surface fabrication in R-MEDM. Electrode vibration provides pulsating movements to dielectric fluid and increases debris velocity which enhances process stability.

EDM process became industrially viable after the discovery of the influence of different dielectric on machining performance. Dielectric fluid used by different micro-electrical discharge machining operation has huge impact on the machining performance like MRR and surface finish. Earlier only hydrocarbon oil was used as dielectric that affects health safety and environment. Through this paper, authors present a literature review on the application of dielectrics which are better substitute to hydrocarbon oil and how hydrocarbon oil can also be used more efficiently. Some of the work depicts that water-based dielectrics can also be used in die sink EDM instead of hydrocarbon oil. Apart from liquid dielectric, micro-EDM is also possible in gaseous media such as oxygen, air, helium, and argon. But gas-assisted micro-EDM needs further more research to make it industrially viable.

Microelectric discharge machining (µEDM) is introduced to the manufacturing industry to produce microfeatures and microholes on difficult to machining materials such as titanium- and nickel-based alloys and other heat-resistant electrically conductive metals and alloys. Even though µEDM can be used to machine any electrically conductive materials, there are many problems to be addressed in order to make it as an accurate and reliable process. Some of the problems associated are low material removal rate, tool wear rate, high surface roughness, and poor dimensional accuracy. This chapter presents powder-mixed microelectric discharge machining as one of the viable alternatives to overcome some of the inherent difficulties associated with microelectric discharge machining process. Suspension of electrically conductive and semiconductive powders in the dielectric can strongly influence the process in a desirable manner. Moreover, the added powder particle gets re-solidified along with the tool material on the machined surface and opens a new possibility to modify the machined surface by selecting the appropriate alloying elements in the required proposition. This approach needs to be thoroughly addressed to explore as ‘µEDM alloying’.

In the current trend of modern technology, demand for accurate miniaturized machined parts made of newly developed extremely hard and brittle materials is increasing continuously and conventional machining and advanced machining processes are becoming obsolete to meet these requirements. Micro-EDM is capable to fabricate micro-tools and miniaturized machined components, but still the machining speed is pretty low. In the µ-EDM process, it is very difficult to remove small debris particles from the vicinity of the narrow machining gap which results in unwanted short circuits and arcing. Especially, due to very small energy of discharge, very low open voltage, and the stray capacitor in the RC type circuits, the machining becomes almost impossible. Thus, to overcome these problems in micro-EDM, vibration can be effectively applied to the tool, workpiece as well as to the machining fluid in order to obtain higher machining speed with high accuracy without significantly increasing the electrode wear.

This chapter accentuates the inherently persistent tool wear issue and its consequences in variants of micro-electro-discharge machining (µ-EDM). The consequences can be seen in the terms of deterioration of precision of the micro-holes and productivity. Although, the tool wear is well explored in μ-EDM and its variant processes, but a very limited efforts have been made to resolve this issue other side. A pulse discrimination system based-real-time tool wear compensation strategy in μ-EDM is anticipated to be a possible technique to get rid of the tool wear issue in μ-EDM drilling. In this regard, an approach which is basically a modification in the existing approach has been discovered and implemented to achieve the desired depth of the micro-hole(s). The proposed approach has been applied to two different work-tool material combinations and input parameters. The potentiality of the approach has been proven results by comparing it with that other trusted techniques like ‘uniform wear method’ (UWM).

In this chapter, different sequential conventional and non-conventional micromachining processes with micro-EDM have been discussed elaborately with their applications in modern-day research and industrial fields. The necessity and advantages of sequential micromachining processes and their difference from hybrid micromachining have been carefully identified. Micro-EDM combined with micro-grinding, micro-milling, micro-turning, micro-ECM, micro-drilling, laser micromachining, LIGA have been discussed with their advantages over respective single processes. The common issues that generally stand in the way of pulling out sequential processes successfully or hamper their accuracy have also been addressed. The chapter also suggests some initiatives to solve those issues. While wrapping up, the chapter emphasizes on the fact that how sequential micromachining, if properly implied, can solve a lot of problems that currently available single processes are dealing with and widen the vast possibility of micromachining of 3D complex structure with high level of accuracy.

Near net shape is a concept that is widely used in the recent years to address the issues of sustainability and resource optimization in the manufacturing sector. Near net shape (NNS) processes are the processes that require least or no post-processing to manufacture a product. Electro-discharge machining (EDM) is a non-conventional machining process that uses spark erosion principle for machining conductive material. If the tool in the EDM is a flexible metallic wire, then the process is termed as wire EDM. Further to this, when the discharge energy, tool and wire diameter, and the machined features are in micron domain, the machining technique is termed μEDM or μWEDM. In μEDM/μWEDM, the resultant structure does not require any post-processing to attain the final dimensional accuracy and surface finish; therefore, these processes can be considered as NNS processes. In this chapter, different applications of μEDM and μWEDM have been discussed as NNS process.

Micro-Electrochemical Discharge Machining (μ-ECDM) is non-contact type hybrid/combined machining process which comprises two dissimilar energies as thermal and electrochemical. In simple, it is developed by comprising of two non-contact based Unconventional Machining Processes (UMPs) as Electro-Discharge Machining (EDM) and Electrochemical Machining (ECM) positively. It is broadly accepted process that applied in different areas of micro-machining and micro-fabrication related to ceramics especially glass, quartz, and Pyrex. However, it shows potential in shaping of difficult-to-shape electrically conductive materials (heat-treated alloys, titanium alloys, superalloys, Inconel, and composites) also. It is utilized for manufacturing of micro-profiles like through/blind μ-holes, μ-chutes, μ-channels, μ-slots, μ-grooves, and complex 3D μ-profiles. The basic functions of the μ-ECDM process are as to eradicate the drawback of EDM and ECM to need of electrical conductivity for machining and also to create micro-/nano-profiles on surface of ceramics. Here, the material can be removed by chemical etching, melting, and vaporization. The present chapter covers various factors related to the μ-ECDM as machining mechanism, machining system, configurations, parameters (control and performance), and process capabilities that make easier to understand the basic concept of μ-ECDM process.

The demand of micro-machining with a diameter ranging from microns to some hundred is rising gradually in the field of aerospace, biomaterials, electronics, and automobiles, due to its noteworthy applications and benefits in miniaturized merchandises and gadgets. µ-EDM is the well-known non-traditional method used for making micro-metallic holes with assorted benefits like its distinguishing non-contact feature and thermoelectric energy between the workpiece to be machined and the electrode to be used. μ-EDM is a modification of the traditional EDM, rendering an imperative function in the generation of micro-features on hard-to-machine materials. In recent years, both processes, i.e., EDM and μ-EDM, are used extensively for production of dies, mold making, cavities, and complex 3D structures. The micro-components are typically finished by hard-to-machine materials and hold multifaceted shaped micro-structures that required accuracy in the level of sub-micron machining. This chapter provides an overview and the theoretical study of the latest 10-year researches from 2009 to 2018 that used decision-making and nature-inspired techniques in optimizing machining parameters of μ-EDM and μ-WEDM processes.