Effect of Dielectric Fluid in EDM: A Review

Exploring the Effects of Dielectric Fluid on EDM

by Snehal C. Sapkale*, Uday A. Dabade,

- Published in Journal of Advances in Science and Technology, E-ISSN: 2230-9659

Volume 13, Issue No. 1, Mar 2017, Pages 390 - 394 (5)

Published by: Ignited Minds Journals

ABSTRACT

Electrical Discharge Machining (EDM) is widely used non-traditional process for the production of miniaturized products with high precision and accuracy. In this process material removal takes place by thermal erosion between workpiece and electrode both of which are dipped in dielectric fluid. Initially, high voltage is applied, when current pass through circuit, about 8000-10000 0C temperature is created causing to melt and vaporize the area of workpiece. In electrical discharge machining (EDM), the working fluid plays an important role affecting the different response variables such a material removal rate, surface finish, etc. The machining characteristics are greatly influenced by dielectric fluid used in EDM. Health, safety and environment are important factors, especially when hydrocarbon based dielectric fluids are used. Due to release of toxic emission products cause environmental impact, operator health issues due to release of toxic fumes, vapours and aerosols during the process, also fire hazards and electromagnetic radiations are harmful. Non-biodegradable wastes are generated. To rectify these problems, replacement of dielectric fluid is main concerns in EDM research. This paper presents literature review of different dielectric fluids used and their effects on different response variables and characteristics of machining. This paper suggests that vegetable oil may be an alternative.

KEYWORD

Electrical Discharge Machining, Dielectric Fluid, Thermal Erosion, Material Removal Rate, Surface Finish, Health Safety, Environment, Toxic Emissions, Non-Biodegradable Wastes, Vegetable Oil

1. INTRODUCTION

With the development of micro-electromechanical systems (MEMS) and devices, micromachining has gained much importance in manufacturing industry. Need for mass manufacturing of miniaturized product is growing. Miniaturized products from different super alloys are required for industries such as aerospace, automotive, biomedical and military applications, etc. Many non-traditional machining methods which are developed in recent years are able to meet these demands [1]. Electrical Discharge Machining (EDM) is one of those non-traditional methods, which is able to machine miniaturized parts with precision and accuracy.

2. LITERATURE REVIEW

A. Electrical Discharge Machining (EDM)

Electrical discharge machining (EDM) is one of the most popular non-traditional material removal processes and has become a basic machining method for the manufacturing industries like aerospace, automotive, nuclear, medical and die-mould production. In this process thermal energy is used to generate heat that melts and vaporizes the work piece by ionization within the dielectric medium. The electrical discharges generate impulsive pressure by dielectric explosion to remove the melted material. Thus, the amount of removed material can be effectively controlled to produce complex and precise machine components.

EDM processes are classified into die-sinking EDM and Wire- EDM. The electrode of die-sinking EDM has the reversed shape of the part to be machined, while Wire-EDM uses thin wire, ranging from 0.01 to 0.36 mm in diameter, as the electrode [2].

B. Mechanism of Material Removal

The mechanism of material removal in the EDM process can be explained with the help of figure 1. When small gap is maintained between electrode and workpiece, discharge built up and free positive ions and electrons are accelerated. They gain very high speed and rapidly form a conductive channel called plasma channel, as in figure 1(a). At this stage the current flow and the spark builds up between the electrodes resulting in a large number of collisions. Temperature within that plasma channel is about 8000-10000 0C which causes local and instantaneous melting of material at the surfaces as shown in figure

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melted material out of that channel as in figure 1(c). The eroded material then resolidifies in the dielectric in the form of small spheres and is evacuated by the dielectric [3].

Dielectric fluid plays very important role in electrical discharge machining. Different response parameters such as material removal rate (MRR), tool wear rate (TWR), surface roughness (SR), recast layer, hardness etc. are affected greatly by dielectric fluid used in EDM. Therefore, literature review is carried out with respect to the effect of dielectric fluid used on response parameters and tabulated in table 1.

Fig. 1 Principle of EDM process (a) Plasma channel created (b) Melting of material (c) Burst bubble [3]

Kibria et al. [4] addresses the issues of micro-EDM using different types of dielectrics and the influence of these dielectrics on the performance criteria. Figure 2 and 3 show the comparative plots of the MRR and TWR, respectively using different dielectrics for varying pulse-on-time (Ton). MRR is high with deionized water than kerosene for all considered settings during experimentation. When hydrocarbon oil was used, the decomposed carbon adhered to the surface of the electrode and titanium carbide (TiC) was formed on the workpiece surface. As the carbide has a higher melting point, the impulsive force during discharge is unstable, thus reducing the material removal rate. When distilled water was used, no carbon adhered to the surface of the electrode and titanium oxide (TiO2) was formed on the workpiece surface. As the oxide has a lower melting point than the carbide, the impulsive force of discharge was much more stable and the material removal rate was higher.

Fig. 2 Variation of material removal rate (MRR) with pulse duration (Ton) at fixed peak current (Ip) of 2A for different dielectrics [4]

Figure 3 reveals that TWR is high using deionized water compared to kerosene dielectric. Kerosene decomposes at elevated temperature and produces carbon particles that adhere to tool electrode surface. These carbon particles restrict the rapid wear of the tool. But deionized water does not produce any carbon during machining and thus no such protective carbon layer formed on the tool surface. But in contrast, more burning occurs in the discharge zone causing more tool wear with deionized water. When machining is done with boron carbide abrasive mixed to both dielectrics, the tool wear is less due to the presence of more number of carbon particles evolving from the decomposition of dielectrics as well as boron carbide abrasive in the machining zone [4].

Fig. 3 Variation of tool wear rate (TWR) with pulse duration (Ton) at fixed peak current (Ip) of 2A for different dielectrics [4]

Snehal C. Sapkale1*, Uday A. Dabade2 3

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3. CONCLUSIONS

Work has been carried out on effect of different dielectric fluids used in EDM. Some of them are regarding literature survey on effects of dielectric fluid while others have carried out experiments with different dielectric fluids. Hydrocarbon oil gives better results in die sinking EDM but hazardous fumes from oil affects environment and health of the operator. Some experiments were performed with water based fluids like distilled or deionised water, tap water etc. It resulted in better MRR, less TWR and better surface finish but recast layer and micro-cracks are produced. Feasibility of adding powder additives to dielectric fluid were studied. Such a dielectric fluid with powder additives provided better results in all aspects than original fluid. But to obtain better results it is necessary to provide ultrasonic vibrations, therefore system becomes bulky and add cost also. At the same time it gives rise to more aerosol emissions which are harmful to the environment as well as health of the operator. Experiments with vegetable oil resulted in better performance than conventional fluids. As vegetable oils are biodegradable, neither they harm environment nor health of the operator and thus may be an alternative solution to conventional dielectric fluids. But further study is necessary in this regard.

REFERENCES

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Snehal C. Sapkale1*, Uday A. Dabade2 3

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Corresponding Author Snehal C. Sapkale*

Walchand College of Engineering, Sangli

E-Mail – sapkalesnehal93@gmail.com