Engineering Questions with Answers - Multiple Choice Questions
Manufacturing Processes – Wire-cut EDM – 6
1 - Question
Copper is not used for making electrode wires in wire cut EDM because of its _____
a) Good conductivity
b) lower tensile strength
c) high melting point
d) higher purchasing cost
Explanation: The low tensile strength of copper wire made it subject to wire breaks when too much tension was applied. Poor flushability was another problem, due to coppers high thermal conductivity. A good portion of the heat from the EDM spark was transferred to the wire and carried away from the workzone instead of using that heat to melt and vaporize the workpiece
2 - Question
Which of the following materials is not used for electrode wires?
Explanation: There is a vast array of wires to choose from with brass wire normally being used however, molybdenum, graphitized, and thick and thin layered composite wires are available for different applications.
3 - Question
Selection of the wire is based on how many factors?
Explanation: The selection of wires is dependent on the following factors: • Cutting speeds (for good cutting speeds, coated wires are used) • Taper angles to be machined • Tensile strength (for cutting thick workpieces, wires of high tensile strengths are used) • Flushability.
4 - Question
The diameter of the electrode wire is in the range of _____
a) 0.001″ – 0.0035″
b) 0.003″ – 0.004″
c) 0.004″ – 0.014″
d) 0.020″ – 0.032″
Explanation: Wire diameters range from .004″ through .014″ with .010″ being the most commonly used. The wire originates from a supply spool, then passes through a tension device (different diameter wires require different amounts of tension to keep it straight). It then comes in contact with power feed contacts where the electric current is applied.
5 - Question
After originating from a supply spool, the wire is passed through _____
a) a chamber filled with special stones
b) diamond guides
c) a furnace
d) a container filled with anti-oxidant
Explanation: After originating from a supply spool, the wire then passes through a set of precision, round diamond guides, and is then transported into a waste bin. The wire can only be used once, due to it being eroded from the EDM process.
6 - Question
With the addition of the programmable _____ to wire cut EDM machine, workpieces of different thicknesses can be machined.
Explanation: With the addition of the programmable “Z” axis, workpieces of different thickness, can also be machined. For example, the die openings and dowel pin holes can be machined on a one inch thick die block, then the machine can be programmed to move to another location and machine the punches on a two or three inch thick workpiece.
7 - Question
In a wire break situation, the end of the wire is_____ while the supply wire is _____
a) clamped, drawn back
b) drawn back, clamped
c) dipped in the di-electric fluid, clamped
d) welded with the other wire, drawn back
Explanation: The threading process of the automatic wire threader takes place automatically if there is a broken wire or by a command in the program. In a wire break situation, the end of the wire is clamped while the supply wire is drawn back, annealing and separating the wire, while leaving a sharp point on the end of the supply wire.
8 - Question
The automatic wire threading offers the ability to cut multiple openings in a workpiece without operator intervention.
Explanation: This feature allows multiple openings to be cut in die blocks, progressive dies, production, and prototype workpieces automatically and unattended without the intervention of an operator, resulting in higher productivity. The demand for automatic wire threading (AWT) and dependent reliability has been met with new and improved designs.
9 - Question
If there is a wire break during machining, the machine returns to the start point.
Explanation: If there is a wire break during machining, the machine returns to the start point of that opening, re-threads the wire and move through the program path to the position where it broke, powers up, and continues cutting as if the wire had never broken.
10 - Question
After a wire break, the wire tip segment that was clamped is disposed off in a wire tip disposal unit.
Explanation: The wire tip segment that was clamped is disposed of in a wire tip disposal unit. The supply wire is then directed into the lower guide. The wire then proceeds to the back of the machine where it is discarded in a scrap wire bin.