Manufacturing Processes Multiple Choice Questions on “Laser Beam Machining – 3”.
1. The flash tube is operated in _____ mode.
a) pulsed
b) continuous
c) reversed
d) synchronous
Answer: a
Clarification: The flash tube is operated in pulsed mode by charging and discharging of the capacitor. Thus the pulse on time is decided by the resistance on the flash tube side and pulse off time is decided by the charging resistance. There is also a high voltage switching supply for initiation of pulses.
2. How many types of flows are possible in gas lasers?
a) 2
b) 3
c) 4
d) 5
Answer: b
Clarification: Gas lasers can be:
• Axial flow
• Transverse flow
• Folded flow.
3. The power of CO2 laser is around______
a) 15 Watt per meter of tube length
b) 55 Watt per meter of tube length
c) 100 Watt per meter of tube length
d) 1 MW per meter of tube length
Answer: c
Clarification: The power of a CO2 laser is typically around 100 Watt per metre of tube length. Thus to make a high power laser, a rather long tube is required which is quite inconvenient. For optimal use of floor space, high-powered CO2 lasers are made of folded design.
4. In a CO2 laser, a mixture of _____ is circulated through the gas tube.
a) CO2, N2 and He
b) CO2, N2 and Ar
c) CO2, H2 and N2
d) CO2, I2 and O2
Answer: a
Clarification: In a CO2 laser, a mixture of CO2, N2 and He continuously circulate through the gas tube. Such continuous recirculation of gas is done to minimize consumption of gases.
5. In CO2 laser, ‘He’ gas is used for cooling purpose.
a) True
b) False
Answer: a
Clarification: CO2 acts as the main lasing medium whereas nitrogen helps in sustaining the gas plasma. Helium on the other hand helps in cooling the gases. High voltage is applied at the two ends of the tube leading to discharge and formation of gas plasma.
6. CO2 lasers are folded to achieve _____________
a) high power
b) high depth of cuts
c) high material removal rate
d) avoid over heating
Answer: a
Clarification: CO2 lasers are folded to achieve high power. In folded laser, there would be a few 100% reflective turning mirrors for manoeuvring the laser beam from the gas supply as well as a high voltage supply.
7. Nd-YAG laser can be used for drilling holes in the range of _____ diameter.
a) 0.25 mm – 1.5 mm
b) 1 mm – 1.5 mm
c) 1.5 mm – 2 mm
d) 2 mm – 2.5 mm
Answer: a
Clarification: For drilling holes as small as 0.25mm and as large as 1.5mm diameter, following lasers are used;
• Nd-YAG,
• Nd-glass, and
• Ruby.
8. For which of the following materials CO2 laser is not used?
a) Plastics
b) Metals
c) Organic materials
d) Ceramics
Answer: b
Clarification: For,
• Plastics— CO2 laser is used
• Metals—Nd-YAG, Ruby, Nd-glass lasers are used
• Organic materials and non-metals—Pulsed CO2 laser is used
• Ceramics—Pulsed CO2, Nd-YAG lasers are used.
9. Which of the following does not hold true about laser beam machining?
a) High initial cost
b) High running cost
c) No heat affected zone
d) It is not suitable for heat sensitive materials
Answer: c
Clarification: Following are the limitations of laser beam machining;
• High initial capital cost
• High maintenance cost
• Not very efficient process
• Presence of Heat Affected Zone – specially in gas assist CO2 laser cutting
• Thermal process – not suitable for heat sensitive materials like aluminium glass fibre laminate.
10. Using lasers, large aspect ratio in drilling can be achieved.
a) True
b) False
Answer: a
Clarification: Following are the advantages of laser beam machining:
• In laser machining, there is no physical tool. Thus no machining force or wear of the tool takes place.
• Large aspect ratio in laser drilling can be achieved along with acceptable accuracy or dimension, form or location
• Micro-holes can be drilled in difficult – to – machine materials
• Though laser processing is a thermal processing but heat affected zone especially in pulse laser processing is not very significant due to the shorter pulse duration.