ECDM process(combination of ECM and EDM process) for non conducting materials.

1. Spark generation in Electrochemical
discharge machining(ECDM) of non-conducting
materials
AKHIL .R
S7 ME,12
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2. 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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Types of process
• Electro-Chemical
ECM process
• Electro-Thermal
EDM process
• Hybrid Thermal
ECDM process

4. 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

6. 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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7. Experimental setup of ECDM Process
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ECDM
Fig.: ECDM Process
Components

9. Types of tool used
• Cylindrical Tool (Conventional Tool)
• Tapered Tool
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10. Why Tapered Tool Electrode?
• 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.
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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.
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11. 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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12. Energy distribution of sparks
(a) Tapered tool electrode (b) Cylindrical tool electrode
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13. Finite element simulation of current density in electro chemical
reaction
(a)Cylindrical electrode (b) Tapered electrode
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14. 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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15. 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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16. 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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17. Working Principle
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18. Tapered tool electrodes with different shape
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19. 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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20. 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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21. 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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22. 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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