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-flow separation and formation of eddies

-evolution of hydrogen

•Typical electrolytes are,

Alloy	Electrolyte
Iron based	Chloride solutions in water (mostly 20% NaCl)
Ni based	HCl or mixture of brine and H2SO4
Ti based	10% hydroflouric acid + 10% HCl + 10% HNO3
Co-Cr-W based	NaCl
WC based	strong alkaline solutions

•Summary of ECM characteristics,

-mechanics of material removal - electrolysis

-medium - conducting electrolyte

-tool material - Cu, brass, steel

-material/tool wear - infinite

-gap 50 to 300 m

-maximum mrr 15*103 mm3/min

-specific power consumption 7W/mm3/min

-critical parameters - voltage, current, feed rate, electrolyte, electrolyte conductivity

-materials application - all conducting metals and alloys

-shape application - blind complex cavities, curved surfaces, through cutting, large through cavities.

-limitations - high specific energy consumption (about 150 times that required for conventional processes), not applicable with electrically non-conducting materials and jobs with very small dimensions, expensive machines.

-surface finishes down to 25 in.

•This technique has been combined with a metal grinding wheel in a process called Electrolytic drilling. The wheel does not touch the work, and gives a surface finish from 8 to 20 in.

59.1 REFERENCES

Ghosh, A., Manufacturing Science, Ellis Horwood Ltd., Chichester, UK, 1986.

Krar,

59.2 PRACTICE PROBLEMS

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1.

a)ECM is used to remove metal from an iron workpiece. The feature being cut is a square hole 1cm by 0.5 cm. To cut down 1cm/min, what current is generally required?

b)How would the current change if the part was 3% carbon?

c)What advantages does ECM have over EDM?

2.We have a metal alloy that is a combination of Zinc and Silicon, but we are unsure what the ratio of the metals is. But an ECM machine can cut a 5mm square hole 2mm deep at a current of ___________ in one minute. What percentage of the alloy is zinc?

3.Describe good applications for EDM.

4.Explain how EDM is best suited to producing complex internal features, such as sharp inside corners.

5.Wire EDM produces parts with a profile that is vertical. What types of applications is this well suited to? Are there particular dies that benefit from this technique?

6.A hole that is 70mm deep and 10mm in diameter. What is the machining time using a) EDM, b) ECM?

7.Which of the following materials are suitable for EDM, EBM, ECM? State Why? a) stainless steel, b) ceramics, c) quartz, d) thermoset plastic, d) copper, e) diamond.

8.Describe the ability of EDM, EBM, ECM to produce sharp corners.

9.Describe the basic operation of an EDM machine using figures. Show why corners are rounded and why flushing is important.