This set of Manufacturing Processes Multiple Choice Questions & Answers (MCQs) focuses on “Laser Welding – 1”.
1. Laser beam welding is a ______ joining process.
Explanation: Laser is an acronym for light amplification by stimulated emission of radiation. Laser Beam Welding (LBW) is a fusion joining process that produces coalescence of materials with the heat obtained from a concentrated beam of coherent, monochromatic light impinging on the joint to be welded.
2. Which of the following is used to direct laser beam?
a) glass apertures
b) perforated glass sheets
c) flat optical elements
d) electro-magnetic coils
Explanation: In the LBM process, the laser beam is directed by flat optical elements, such as mirrors and then focused to a small spot (for high power density) at the workpiece using either reflective focusing elements or lenses.
3. Inert gas shielding is generally employed to protect _____
a) laser beam
b) molten puddle of metal
c) filler electrode
Explanation: It is a non-contact process, requiring no pressure to be applied. Inert gas shielding is generally employed to prevent oxidation of the molten puddle and filler metals may be occasionally used.
4. Which of the following is a commercially used laser?
a) Nd-GAG laser
b) 1.06 µm wavelength CO2 laser
c) 2 µm wavelength CO2 laser
d) Nd- YAS laser
Explanation: The Lasers which are predominantly being used for industrial material processing and welding tasks are the Nd-YAG laser and 1.06 µm wavelength CO2 laser, with the active elements most commonly employed in these two varieties of lasers being the neodymium (Nd) ion and the CO2 molecules respectively.
5. In solid state laser _____ is used as a dopant.
a) actinium ion
b) neodymium ion
c) platinum ion
d) lead ion
Explanation: It utilizes an impurity in a host material as the active medium. Thus, the neodymium ion (Nd+++) is used as a ‘dopant’, or purposely added impurity in either a glass or YAG crystal and the 1.06 µm output wavelength is dictated by the neodymium ion.
6. The lasing material is a cylinder of a diameter of about _____ mm.
Explanation: The lasing material or the host is in the form of a cylinder of about 150 mm long and 9 mm in diameter. Both ends of the cylinder are made flat and parallel to each other.
7. The lasing material or crystal is excited by _____
a) neon lamps
b) krypton lamps
c) tungsten wire laps
Explanation: Both ends of the cylinder are made flat and parallel to very close tolerances, then polished to a good optical finish and silvered to make a reflective surface. The crystal is excited by means of an intense krypton or xenon lamps.
8. Which of the following laser is the most efficient?
a) CO2 lasers
b) Nd-YAG lasers
c) Ruby lasers
d) Dye lasers
Explanation: The electric discharge style CO2 gas lasers are the most efficient type currently available for high power laser beam material processing. Dye lasers use complex organic dyes like rhodamine 6G.
9. CO2 lasers employs gas mixture of _____
a) nitrogen and helium
b) hydrogen and helium
c) argon and xenon
d) oxygen and nitrogen
Explanation: These lasers employ gas mixtures primarily containing nitrogen and helium along with a small percentage of carbon dioxide, and an electric glow discharge is used to pump this laser medium.
10. Gas heating produced by gas lasers is controlled by _____
b) a blow of cool air
c) adjusting the wavelength of the laser
d) circulating the gas mixture
Explanation: Gas heating produced by gas lasers is controlled by continuously circulating the gas mixture through the optical cavity area and the thus CO2 lasers are usually categorized according to the type of gas flow in the system.
11. How many categorize are there of CO2 lasers?
Explanation: CO2 laser are usually categorized according to the type of gas flow in the type of gas flow in the system:
• slow axial
• fast axial
• transverse axial.
12. Slow axial flow gas lasers are simplest of the CO2 lasers.
Explanation: They are the simplest of the CO2 lasers. Gas flow in the same direction as the laser resonator’s optical axis and electric excitation field, or gas discharge path. These lasers are capable of generating laser beams with a continuous power rating.
13. Solid axial flow CO2 lasers can generate laser beams with a constant rating of 80 Watts.
Explanation: These lasers can generate laser beams with a constant rating of approximately 80 Watts for every meter of discharge length. A folded tube configuration is used for achieving output power levels of 50 to 1000 Watts, maximum.
Sanfoundry Global Education & Learning Series – Manufacturing Processes.
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