Download Assignment _05

Manufacturing Process Technology part-2
Assignment – 05
1. Which of the following materials is/are used for Electrical Discharge Machining (EDM)
process?
(a) Brass
(b) Copper
(c) Graphite
(d) All of the above
2. In Electrical Discharge Machining (EDM) process the metal removal is carried out by
(a) electrolysis
(b) melting and vaporization
(c) fracture of work material due to impact of grains
(d) none of the above
3. For maximum power delivery through the circuit during EDM, ratio of the breakdown
voltage to supply voltage is
(a) 0.72
(b) 1 (c) 0.75
(d) 0.65
4. Servomechanism in EDM operates when there is
(a) short circuit
(b) high IEG
(c) low IEG
(d) all of these.
5. If in a RC type generator, to get an idle time of 500 μs for open circuit voltage of 100 V
and maximum charging voltage of 70 V, determine charging resistance. Assume C = 100
μF.
(a) 6 ohm
(b) 6 milli ohm
(c) 0.6 ohm
(d) none of these.
6. Relative electrode wear during EDM is
(a) <100%
(b) >100 %
(c) =100 %
(d) none of these
7. Location of spark generated during EDM is
(a) random
(b) governed by dielectric strength
(c) governed by surface finish of tool and workpiece both
(d) none of these.
8. Stratified wires is used in wire EDM so that they can
MOOC course under NPTEL (July 2016)
IIT Kanpur
Manufacturing Process Technology part-2
Assignment – 05
(a) withstand more mechanical forces
(b) carry more heat energy
(c) both of these
(d) none of these
9. If the flushing system of EDM machine is inefficient the machining cycle time will be
(a) longer
(b) shorter
(c) no effect
(d) no definite trend
10. In a typical EDM machining operation, the pulse ‘off’ time is 30 % of the total time. What
will be duty cycle?
(a) 70 %
(b) 30 %
(c) 2.3 %
(d) 0.42 %
11. An electric discharge machining operation is being performed on tungsten (melting
temperature = 34100 C). (i) Determine the amount of metal removed in the operation after
one hour at a discharge amperage = 20 amps. (ii) If the work material were tin (melting
temperature = 2320 C), determine the amount of material removed in the same time. Take
constant of proportionality = 664.
(a) 2159 mm3 & 58,878 mm3
(b) 2159 cm3 & 58,878 mm3
(c) 215.9 cm3 & 58.878 mm3
(d) 2159 mm3 & 588.78 mm3
12. A metal removal rate of 0.01 mm3/sec is achieved in a certain EDM operation on a pure
iron (melting temperature = 15380 C) workpart. What metal removal rate would be
achieved on nickel (melting temperature = 14550 C) in this EDM operation, if the same
discharge current were used?
(a) 0.001 mm3/sec
(b) 0.001 mm3/min
(c) 0.01 mm3/sec
(d) 0.01 mm3/min
13. In a wire EDM operation performed on 7 mm thick C1080 steel (melting temperature =
15000 C) using a tungsten wire electrode whose diameter = 0.125 mm. Past experience
suggests that the overcut will be 0.02 mm, so that the kerf width will be 0.165 mm. Using
a discharge current = 10 amps, what is the allowable feed rate that can be used in the
operation?
(a) 42.79 mm/min
(b) 42.79 cm/min
MOOC course under NPTEL (July 2016)
IIT Kanpur
Manufacturing Process Technology part-2
Assignment – 05
(c) 4.279cm/sec
(d) none of these
14. A wire EDM operation is to be performed on a slab of 3/4 inch thick aluminum (melting
temperature = 6600 C) using a brass wire electrode whose diameter = 0.005 in. It is
anticipated that the overcut will be 0.001 in, so that the kerf width will be 0.007 in. Using
a discharge current = 7 amps, what is the expected allowable feed rate that can be used in
the operation?
(c) 0.467 mm/sec
(d) 1.083 in/sec
(a) 0.467 in/min
(b) 1.083 in/min
15. A wire EDM operation is used to cut out punch and die components from 25 mm thick tool
steel plates. However, in preliminary cuts, the surface finish on the cut edge is poor. What
changes in discharge current and frequency of discharges should be made to improve the
finish?
(a) by increasing discharge current and increasing frequency of discharges
(b) by reducing discharge current and increasing frequency of discharges.
(c) by increasing discharge current and decreasing frequency of discharges
(d) none of these
MOOC course under NPTEL (July 2016)
IIT Kanpur