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Which one he following statements is true for Electrical Discharge machining (EDM)?
i. The material removal takes place due to the melting and evaporation of the workpiece material.
ii. Any electrical conductor can be machined by this method.
iii. Some light oil like transformer oil or kerosene oil is used as dielectric.
Only i
i & ii
i, ii & iii
ii & iii
During EDM, the temperature developed at the point of spark is of the order of
2,000°C
6,000°C
10,000°C
14,000°C
Which one of the following statements is not true in case of EDM?
Erosion takes place both on work piece and tool.
Gap between tool and work piece is controlled by servo mechanism.
The electrode (tool) is made of graphite or copper.
The size of impression on the work piece surface is exactly same as that of electrode (tool).
The EDM process is (select the correct answer)
Burr free
Not useful for hard metals
Direct contact machining
Capable of producing sharp corners
Location of spark generated during EDM is
Random
governed by dielectric strength
governed by the surface finish of the tool and work piece both
none of these.
Feed to the electrode during EDM is given
to maintain constant velocity of dielectric flow in the IEG
to maintain constant IEG
to maintain constant current density
none of these
If the flushing system of the EDM machine is inefficient the machining cycle time will be
Longer
Shorter
no effect
no definite trend
Preferable tool properties in EDM are
High electrical conductivity, low thermal conductivity
low electrical conductivity, High thermal conductivity
High electrical conductivity, High thermal conductivity
low electrical conductivity, low thermal conductivity
During calculation of MRR in EDM, supply voltage was used as 60V in place of the actual supply voltage of 40V. What is the ratio of actual and calculated MRR? Assume that the condition for maximum power delivery to the discharging circuit is satisfied.
1.5
0.44
2.25
None
In EDM the metal removal is carried out by
fracture of work material due to impact of grains
electrolysis
melting and vaporization
none of the above
The spark gap in EDM process is maintained such that
the gap voltage is around 99% of supply voltage
the gap voltage is around 70% of supply voltage
the gap voltage is around 50% of supply voltage
the gap voltage is around 10% of supply voltage
Deionized water is used as dielectric in
wire-EDM
electric discharge grinding
electric discharge diamond grinding
Ineffective flushing results in
High MRR
Poor surface finish
Low MRR
High surface finish
Arcs are undesirable in EDM due to
Tool damage
Workpiece damage
None of the above
Undesirable characteristic of graphite electrode is
Higher TWR
Poor surface finish
Brittleness
All of the above
Relative electrode wear (REW) during EDM is
<100%
>100%
100%
none of these,
Stratified wires are used so that they can
withstand more mechanical forces
carry more heat energy
both of these
none of these
Wear of tool during EDM process would result in
deeper hole
lesser diameter hole
both
none.
EDM is not suitable for machining of
Very hard metals,
Glass,
Plastics,
Fragile metallic components.
Electrode refeed system in EDM is used to compensate wear in
Length
Diameter
Both
none.