Hybrid

Electrochemical Discharge

Machining(ECDM)

Presented by

Ajay Vaishnav

TME15B001

Contents:-IntroductionNeed of ECDMWorking Principle of ECDMMaterial Removal Mechanism in ECDMMain Influencing parametersAdvantages over ECM/EDMDisadvantages over EDM/ECMApplication of ECDMComparison between ECDM, EDM and ECM

• Electro-Chemical processECM

3

• Electro-Thermal processEDM

• Hybrid Thermal processECDM

What is ECDM ?

• Material removal due to Erosion of work piece at high temperature and high pressure.

EDM

• Material removal due to Anodic dissolution of work piece. ECM

• Material removal due to Thermal heating/melting and chemical etching of the work piece.

ECDM4

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). Non-

conducting materials can be machined by ECDM by

employing auxiliary electrodes.

5

Need of ECDM

1.High Accuracy and Surface Finish2.High Strength Alloys3.Complex Surfaces4.Technology Advancement5.Machining on non-conducting

materials

.

Material Removal Mechanism

in ECDM :-MRR

Mechanism

Thermal mode

Melting Vaporization

Chemical mode

Etching/E-C Rxn

Mechanism

(auxiliary electrode)

BASIC MECHANISM OF

Electro-chemical discharge machining

(ECDM)

The tool electrode (cathode) and auxiliary electrode (anode) are immersed in an electrolyte solution (typically NaOH or KOH). Both electrodes are connected to a DC power supply, causing hydrogen bubbles to be produced on both electrodes due to electrochemical reactions. The bubbles become dense and coalesce into a gas film (Passivating Film) on the tool electrode. The gas film allows sparking between the tool electrode and electrolyte by isolating the tool from the surrounding electrolyte. If the workpiece is brought close to the tool, material removal occurs.

Main Influencing parameters :-

Electrolyte Semi Dielectric fluids/Electrolyte

Voltage 40-150V, DC & Current 3-4A

Gas Film (Passivating Film)

Spark Generation

Tool Electrode

Auxiliary Electrode

Electrode Gap

Tool PropertiesHigh Electrical & Thermal conductivity

High melting point

Cheapness

Good wear resistance Eg. Steel,Cu

1.Cylindrical Tool (Conventional Tool)

2.Tapered Tool12

Why Tapered Tool Electrode?

Fringing effect

13

• 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.

By replacing the cylindrical tool with a tapered end tool, we make discharges focus on a concentrated region.

Tapered tool electrodes with different shape

14

Some Other Tools

Effect of Voltage

Increase in applied voltage increases the MRR

But Less than 100V is best.

Question: Why Higher voltage is not preferred ?

Ans.: MRR start decreasing due to entrapping of debris in spark gap

Function of Electrolyte

Maintain constant resistance across the gap

Cools the spark region

Removes eroded particles

Avoid welding of tool and work

Examples:- aqu solution of KOH or NaOH, sodium silicate or nitrate

Effect of Electrolyte

Concentration

Concentration MRR

Concentration Smoother Surface finish

But concentration(typically NAOH) < 250g/L

Why ????

Some More Parameters

Effect of machining gap

Effect of inter electrode gap

Effect of tool feed rate

Effect of Electrolyte temperature

Advantages over ECM/EDM :-

• The surface obtained have better finish than EDM and ECM 0.01mm or 10 m

• Suitable for non-conducting materials.

• High accuracy.

• Does not leave any chips or burrs.

• Less power consumption.

Advantages over Traditional

Processes Non conducting materials like glass, ceramics etc can be

machined in this process.

Tool wear is negligible compared to other processes.

Focused spark generation due to the tapered tool.

High machining rates are also possible that increasing the

productivity and reducing the unit production cost.

21

Disadvantages over EDM/ECM:-

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

• Energy from the spark is not fully transferred.

• Initial cost is high.

• Thickness of ceramic material can be machined is limited to 1.5 mm.

• Radial overcut.

• The process cannot produce internal and external sharp edges.

What is Radial Overcut ?

Application of ECDM :-

production of :

• Through and blind micro-holes

• Micro-grooves

• Micro-slots

• Micro-channels and Complex shapes produced in non-conducting

materials ( quartz, glass, and ceramics) etc.

• Miniature features of turbine blades

• Industrial applications like bearings, computer parts

Comparison betweenECM, EDM and

ECDM ASPECTS ECM EDM ECDM

PRINCIPLE Anodic dissolution Spark erosion Both

POWER 10,000A,2-3V,DC 200A,50-200V,DC 3-4A,40V,DC

WORK

PIECE

Conductive Conductive Conductive &

non- conductive

MRR Less Less 5times faster

than EDM

TOOL

WEAR

Less than both Higher than ECDM Less than EDM

ACCURACY Higher than EDM Dimensional accurate

:+-.03mm

+-.01mm

SURFACE

FINISH

Higher than both Less Higher than

EDM

COST Less initial than ECDM Less initial than

ECDM

High

25

…..

Questions

Please