This set of Manufacturing Processes Multiple Choice Questions & Answers (MCQs) focuses on “Laser Welding – 2”.
1. ______ is used to circulate the laser gas in case of fast axial flow gas laser.
b) Turbo pump
c) Guide vanes
d) Vane pump
Explanation: In the case of the FAF Laser, a roots blower or turbo pump is used to circulate the laser gas at high speed through the discharge region and corresponding heat exchangers.
2. Fast axial flow gas lasers are available between _____ watts power levels.
Explanation: The fast axial flow lasers with continuous wave (CW) output power levels of between 500 to 6000 watts are available. The fast axial flow lasers have a similar arrangement of components as that of slow axial flow gas laser.
3. In transverse flow type gas lasers, gas is circulated across _____
a) the resonator cavity axis
b) optical axis
c) deflection coils
d) the focusing lens
Explanation: These lasers operate by continuously circulating gas across the resonator cavity axis by means of a high speed fan type blower while maintaining an electric discharge perpendicular to both the gas flow direction and the laser beam’s optical axis. Transverse flow lasers with output power levels between 1 and 25 kW are available.
4. In case of laser welding, heat input is _____ to fuse the weld metal.
a) equal to the required amount
b) close to the minimum required
c) greater by 200 J than required
d) approximately higher by atleast 320 J
Explanation: Following are the few advantages of Laser Beam Welding:
• Heat input is close to the minimum required to fuse the weld metal
• Reduced heat affected zones
• Workpiece distortions are minimized due to smaller heat affected zones.
5. Which of the following holds true about laser welding process?
a) Time for welding thick sections is more in case of LBW
b) Shielding gas is used to melt the burr formed during the machining
c) In LBW, sometimes filler metals are used
d) In Nd- YAG lasers, crystals of C14 are used as the lasing material
Explanation: Time for welding thick sections is reduced and the need for filler wires and elaborate joint preparations is eliminated by employing the single pass laser welding procedures but filler metals may be occasionally used.
6. Laser welding is performed with freedom from electrode contamination.
Explanation: In the case of laser beam welding, no electrodes are required; welding is performed with freedom from electrode contamination, indentation or damage from high resistance welding currents.
7. Which of the following does not hold true about laser beam welding?
a) Laser welding cannot be used in case of joints at intricate locations
b) It can produce tiny welds
c) Laser welding can be used for a variety of metal combinations
d) In case of LBW, thin welds on small diameter wires are less susceptible to burn back
Explanation: Following are the advantages of laser beam welding:
• Welding in areas that are not easily accessible with other means of welding can be done by LBM, since the beams can be focused, aligned and directed by optical elements
• Laser beam can be focused on a small area, permitting the joining of small, closely spaced components with tiny welds
• Wide variety of materials including various combinations can be welded
• Thin welds on small diameter wires are less susceptible to burn back than is the case with arc welding.
8. Laser welds are not influenced by _____
a) electric field
b) magnetic field
c) radio waves
d) ultraviolet rays
Explanation: Laser welds are not influenced by magnetic fields, as in arc and electron beam welds. They also tend to follow weld joint through to the root of the work-piece, even when the beam and joint are not perfectly aligned.
9. Aspect ratios, i.e., depth-to-width ratios of the order of _____ are attainable by LBW.
Explanation: Following are the few advantages of the LBW process:
• Aspect ratios (i.e., depth-to-width ratios) of the order of 10:1 are attainable in LBM
• Metals with dissimilar physical properties, such as electric resistance can also be welded
• No vacuum or X-Ray shielding is required.
10. Weld penetrations of larger than _____ are difficult to weld by LBW.
a) 5 mm
b) 13 mm
c) 19 mm
d) 25 mm
Explanation: The maximum joint thickness that can be welded by a laser beam is somewhat limited. Thus weld penetrations of larger than 19 mms are difficult to weld. Also, joints must be accurately positioned laterally under the beam and at a controlled position with respect to the beam focal point.
11. Which of the following material properties has no effect on laser beam machining?
b) Thermal conductivity
d) Electrical conductivity
Explanation: High reflectivity and high thermal conductivity of materials like Al and Cu alloys can affect the weldability with lasers. Also, in case of mechanical clamping of the weld joints, it must be ensured that the final position of the joint is accurately aligned with the beam impingement point.
12. Lasers tend to have fairly low energy conversion efficiency.
Explanation: Following are the few limitations of the LBM Process:
• An appropriate plasma control device must be employed to ensure the weld reproducibility while performing moderate to high power laser welding
• Lasers tend to have fairly low energy conversion efficiency, generally less than 10 percent
• Some weld-porosity and brittleness can be expected, as a consequence of the rapid solidification characteristics of the LBM.
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