Manufacturing Processes Multiple Choice Questions on “Wire-cut EDM – 3”.
1. Wire electric discharge (ED) machining is based on the same principle as that of _____
a) hydro-dynamic EDM
b) die-sink EDM
c) polar EDM
d) non-conventional EDM
Answer: b
Clarification: Wire electric discharge (ED) machining is based on the same principle as die-sink ED machining. The basic elements in all EDM methods are dielectric fluid, a workpiece and an electrode.
2. The only difference between die-sink EDM and wire cut EDM is the _____
a) way of material removal
b) electrode used for the machining
c) type of materials machined
d) processing time
Answer: b
Clarification: In the die-sink EDM method the electrode has the same shapes as the wished machining results. In the wire cut EDM method the electrode is a moving wire made from some electrically conducting material. The workpiece is cut with the electrode wire.
3. During wire cut EDM, the size of the cavity produced by the wire while machining depends upon _____
a) material of the workpiece
b) di-electric fluid used
c) wire material
d) electric current
Answer: d
Clarification: While machining a high electric current passes through the dielectric fluid and heats the workpiece surface from a very small area. The corresponding workpiece area melts and what is left, is a small round cavity. The cavity size depends on the electric current and potential.
4. Sparking gap is the distance between _____
a) the workpiece and the CNC table
b) the workpiece and the electrode wire
c) the electrode wire and the di-electric fluid
d) the workpiece and the spark plug
Answer: b
Clarification: The distance between the electrode wire and the workpiece is called a sparking gap. The electrode produces shapes that are a sparking gap dimension larger than the programmed shape through which the electrode wire passes.
5. The absolute minimum inner corner radius is _____
a) the wire radius minus the sparking gap
b) the sparking gap minus the wire radius
c) the wire radius plus the sparking gap
d) double of the wire radius
Answer: c
Clarification: The absolute minimum inner corner radius is the wire radius added with the sparking gap . Therefore during machining, the shapes produced have larger dimensions as compared to the shapes mentioned in the program.
6. The wire ED machines have _____ programmable axes.
a) 2
b) 2-5
c) 6
d) 3-9
Answer: b
Clarification: The wire cut EDM machines have 2 – 5 programmable axes. The machines that are used in mould making applications typically have 5 programmable axes. These axes are Wire guide, wire tilting in x and y –directions and workpiece or wire system movements in x and y –directions.
7. Which of the following component of the wire cut EDM machine does not get heated?
a) Workpiece
b) Electrode wire
c) Di-electric fluid
d) Coils
Answer: b
Clarification: The electrode wire moves between two coils with a moderate speed. The part of the wire that actually machines the workpiece is constantly changing. There is no time for the wire to heat up.
8. Which of the following material properties sets restrictions to use wire cut EDM?
a) Material type
b) Melting point
c) Material hardness
d) Electrical conductivity
Answer: d
Clarification: As the electrode wire does not get heated during machining, the problems with electrode wear are not an issue like in the case of die-sink ED machining and it is possible to use wire cut EDM also for materials with high melting ranges. The material hardness sets no restrictions. The only restriction is that the material needs to be electrically conductive.
9. Wires used in wire cut EDM are usually disposed after one usage.
a) True
b) False
Answer: a
Clarification: Despite the minimum wear, wires are usually disposed after one usage. Sparking and high temperature during the machining reduces the wire tensile strength and the wire could easily break if re-used.
10. The electrode wires are usually made form _____
a) graphite
b) iron
c) nickel
d) brass
Answer: d
Clarification: Wire used in wire cut EDM are usually made of brass – either zinc-coated or uncoated. Brass wire can be purchased in different hardnesses and different diameters. Zinc coated wire is used in machining high melting point workpiece materials.