This set of Manufacturing Processes Multiple Choice Questions & Answers (MCQs) focuses on “Wire-cut EDM – 4”.
1. _____ grades wire are used in automatic re-threading mechanisms.
Explanation: The harder grades are used in automatic re-threading mechanisms and also if the machined shapes contain high flat surfaces. Hard wires resist change in direction and for that reason are likely to produce nice flat surfaces.
2. For machining of high melting point materials, _____ wires are used.
b) zinc coated
c) aluminium coated
Explanation: Zinc coated wire is used in machining high melting point workpiece materials. The zinc coating vaporises in lower temperature than the brass core. Vaporisation reduces the amount of heat that transmits to the brass and the core wears less.
3. _____ is/are used as di-electric fluid in die sink EDM process.
a) Pure water
b) Silicone gel
c) Petroleum products
d) Epoxy resins
Explanation: The dielectric fluid in the die-sink EDM process is usually some petroleum product. In the wire cut EDM process, it is most common to use de-ionised water.
4. Which of the following is not the application of wire cut EDM process?
a) Machining ejector holes
b) Cutting the ejector pins
c) Machining cores of various moulds
d) Machining of complex shapes made of plastic
Explanation: The most typical wire cut EDM applications in mould making are: −
• Machining ejector holes
• Shaping and cutting the ejector pin ends to follow mould cavity surface shapes
• Machining cores and corresponding fastening holes in the mould plates and inserts.
5. During mould making by wire cut EDM, it is important to harden ______ to counter the effects of changes in the shape of the workpiece due to heat treatment.
a) the insert
b) electrode wire
c) electrode holding coils
d) bolting points in the workpiece
Explanation: It is important to harden the insert or mould plate steel before making the tightly tolerated ends in the ejector pin holes because the heat treatment tends to change the workpiece shapes at a certain degree.
6. Which of the following machining process is usually preferred for cutting of ejectors which are used in mould making?
c) Wire-cut EDM
d) Die sink EDM
Explanation: There is a need to cut the ejector to a right dimension and if the cavity surface is shaped there is also a need to shape the ejector end. The wire ED machine is one of the most accurate machines in mould shops and usually there is also free machining time available. Another option is to cut and shape the ejectors in a milling machine, but the most accurate milling machines are used in mould cavity machining operations and normally they are rather busy for long periods of time.
7. How many ways are there for making the fixed cores by wire cut EDM process?
Explanation: Basically there are two options for making the fixed cores:
− Machine the cores directly to the mould insert plate or mould plate
− Machine the cores to separate pieces of mould steel and attach the piece to the mould assembly.
8. The selection of the manufacturing process depends upon ____________
a) chemical reactivity between the mould material and the di-electric fluid
b) mould shape
c) application of the mould
d) number of parts to be machined
Explanation: The selection depends on the core dimensions and shapes. High and narrow cores or cores with sharp shapes are easiest to manufacture with separate parts. Special cases are core pins. Core pins are used in making small diameter holes to castings.
9. The wire EDM process is used for making moulds with high drafted walls.
Explanation: Like every wall in the mould opening direction, the core walls are also drafted. It is rather difficult to make high drafted walls with a milling machine. Especially in the case of injection moulding or high pressure die casting moulds where the accuracy requirements are very high. The wire ED machine produces these shapes accurately with ease.
10. For manufacturing of complex shapes, soft electrode wires are used.
Explanation: Soft wires are useful in applications with complex shapes, where the machine changes the wire tilting angle several times. The harder grades are used in automatic re-threading mechanisms.
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