Spark generation in Electrochemical

discharge machining(ECDM) of non-

conducting materials

AKHIL .R

S7 ME,12

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Contents

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• Introduction

• Operation of ECDM

• Types of Tool Electrode

• Advantages of ECDM

• Disadvantages of ECDM

• Conclusion

• References

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• Electro-Chemical processECM

• Electro-Thermal processEDM

• Hybrid Thermal processECDM

Types of process

Introduction

Electro-chemical discharge machining (ECDM) is a hybrid

non-conventional manufacturing process which combines the

features of electro-chemical machining (ECM) and electro

discharge machining (EDM).The demand of non-conductive

material has grown rapidly with the broad application in optical,

electrical and mechanical systems.

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• Material removal due to Erosion of workpiece at high temperature and high pressure. EDM

• Material removal due to Anodic dissolution of workpiece. ECM

• Material removal due to Thermal heating/melting and chemical etching of the workpiece.ECDM

Introduction

Electro-chemical discharge machining (ECDM), taking

advantage of electrochemical discharge phenomenon, is a non-

traditional micro-machining process. Non-conducting materials

can be machined by ECDM by employing auxiliary electrodes.

The energy transferred to the material from discharge

activity is converted into heat.If the temperature is high enough,

material will be removed.

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Experimental setup of ECDM Process

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ECDM

Fig.: ECDM Process

Components

Types of tool used

• Cylindrical Tool (Conventional Tool)

• Tapered Tool

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Why Tapered Tool Electrode?

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• Fringing effect,ie,material near the rim of the cylindrical tool was removed,indicating release of sparks were distributed around the rim.

• Current density is more intense near the rim for cylindrical tools. Thus, sparks tend to generate from any point along the rim of the tool electrode, if not considering any geometrical defects.

Why Tapered Tool Electrode?

• By replacing the cylindrical tool with a tapered end tool,

however, could make discharges focus on a concentrated

region.

• Fringing effect existed for cylindrical tools, while tapered tool

has only one spot for spark generation.

• However, sparks can only be generated at the tip of tapered

tools, eliminating the minor discharging effect and thus

increased consistency in spark generation.

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Energy distribution of sparks

(a) Tapered tool electrode (b) Cylindrical tool electrode

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Finite element simulation of current density in electro chemical

reaction

(a)Cylindrical electrode (b) Tapered electrode

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Operation of ECDM

• Tool electrode, made of tungsten rods with 250µm diameter,

acted as the cathode in electrochemical reaction.

• Tool electrode dissolved faster at the rim of the auxiliary

electrode (anode) because of higher intensity of electrical

field.

• The auxiliary electrode is made of stainless steel.

• A tapered tool electrode was fabricated and employed in the experiments to increase the consistency of spark generation.

• The workpiece used is a sheet of soda-lime glass.

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Operation of ECDM

• Tapered tool electrodes were immersed 1mm in the

electrolyte and the tips maintained a 50µm gap from the

workpiece.

• 34 V DC voltage was applied to the electrodes, with

machining time ranging from 0.1s to 1.0s in order to vary total

energy released to workpiece.

• If the electrode voltage is too high,thermal cracks tend to

happen, while a minimum voltage must be maintained to

ignite the electrochemical reaction.

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Operation of ECDM

• The critical temperature of glass is around 600◦C.

• The melting point of Tungsten is 3410◦C.

• The auxiliary electrode is immersed 1mm under the upper surface of the electrolyte.

• As NaOH was chosen as the electrolyte,the following reaction dissolves glass workpiece and generates loose precipitate:

2NaOH + SiO2 → Na2SiO3↓ + H2O

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Working Principle

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Tapered tool electrodes with different shape

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Advantages

• Non conducting materials like glass, ceramics etc can be

machined in this process.

• Tool wear is negligible compared to other non-conventional

processes.

• Increased consistency in spark generation due to the tapered

tool.

• High machining rates are also possible thereby increasing the

productivity and reducing the unit production cost.

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Disadvantages

• Tool is likely to worn out,if the machining time is increased.

• Energy from the spark is not fully transferred.

• The process cannot produce internal and external sharp edges.

• The produced accuracy is low.

• There is difficulty in handling the electrolyte.

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Conclusion

• Tapered tool electrodes were employed as tool electrode in the study of spark generation.

• Tapered tool improved the consistency of spark generation and suppressed the generation of minor discharges.

• A finite element based model was developed to predict the geometry of removed material given specific spark energy input.

• Electrical energy transferred converted into heat source acting on the workpiece in machining process.

• Therefore material removal can be simulated by solving heat transfer problems.

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References

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• Baoyang Jianga, Shuhuai Lana, Jun Nia, Zhaoyang Zhang (2013)_“Experimental investigation of spark generation in electro chemical discharge machining of non-conducting materials”.

• M.L.Harugade, M.V.Kavade, N.V.Hargude_“Effect of electrolyte solution on material removal rate in Electrochemical Discharge Machining”.

• Hassan El-Hofy_“Advanced Machining Processes-Non traditional and Hybrid Machining Processes”.

• P.K.Mishra_“Non Conventional Machining Process”.

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