SECTION-3 (Q/A)

1. What is the working principle of Electrical Discharge machining process?

In electrical discharge machining process, metal is removed by producing powerful electric spark discharge between the tool (cathode) and the work material (anode).

2. What are the factors affecting metal removal rate?

a.  Metal removal rate increases with forced circulation of dielectric fluid.

b. It increases up to optimum value of work-tool gap, after that it drops suddenly. c.  Metal removal rate is maximum when the pressure is below atmospheric.

3. What are the basic requirements of tool material of EDM?

a.  It should have low erosion rate.

b. It should be electrically conductive c.  It should have good mach inability.

d. Melting point of the tool should be high.

4. How the tool materials are classified?

Tool or electrode can be classified into four groups

1. Metallic electrodes :         Brass

Copper tungsten Chromium copper Aluminium tungsten Silver tungsten

2. Non metallic          :          Graphited

3. Combined metallic

and non- metallic :         Copper graphite

4. Metallic coating as

Insulators               :         Copper on moulded Plastic and copper on ceramic.

_{5. Indicate the range of pulse duration and current in EDM?}

The current density in the discharge of channel is of the order of 10,000 A/cm ² . Spark discharge frequencies range from 200-500 KHz pulses per second at voltage level of 30

– 250 V.

6. Give the wear ratio for brass, copper and copper tungsten?

Wear ratio

Brass                          1:1

Copper                       2:1

Copper tungsten        8:1

7. Name the most commonly used spark generating circuits?

a.  Resistance – capacitance circuit (R-C) (or) Relaxation circuit b. R-C-L circuit

c.  Rotary pulse generator circuit

d. Controlled pulse generator circuit

8. What are the draw backs of using relaxation circuit?

a.  Though the discharge current in a relaxation circuit reaches a high value, it is of very short duration.

b. The use of high frequencies is limited, since the time for changing the capacitor is high.

9. What are the advantages of EDM processes?

a.  Machining of very thin section is possible.

b. It does not leave any chips or burrs on the workpiece. c.  It is well suited for complicated components.

d. Since there is no cutting forces act on the job, error due to elastic deformation is eliminated.

e.  Fine holes can be easily drilled.

10. List the applications of EDM?

This is most widely used machining process among the non – traditional machining methods. Its applications are as follows.

a.  Production of complicated and irregular shaped profiles. b. Thread cutting in jobs.

c.  Drilling of micro holes. d. Helical profile drilling. e.  Curved hold drilling.

11. List the advantages of wire cut EDM process?

a.  It gives high surface finish.

b. Complicated shapes can be efficiently machined. c.  Tool manufacturing and storage is avoided.

d. It is economical for small batch production.

12. List the advantages of wire – cut EDM process?

a.  Capital cost is high. b. Cutting rate is slow.

c.  It is not suitable for large workpiece.

13. What is the shape of electrode in traveling wire EDM process?

A very thin wire made of brass or molybdenum having circular cross section is used as electrode in traveling wire EDM process.

14. What is the function of servo mechanism in EDM?

The function of servo mechanism is to maintain very small gap, known as

‘sparkplug’ranges of 0.005 to 0.05 mm between the workpiece and the tool.

15. What is overcutting in EDM process and how is it affected by amphere and frequency?

Overcutting is cutting  of larger cavity than the size of electrode  in EDM

process. It increases with increase in current and decreases at high frequencies.