This set of Manufacturing Processes Multiple Choice Questions & Answers (MCQs) focuses on “Laser Welding – 6”.
1. Weld bead quality and the penetration are functions of _____
a) shroud gas velocity
b) material of the component
c) wavelength of the laser beam
Explanation: Penetration is a function of power and likewise the weld bead quality.
– Too much power causes vaporization and material ejection as in drilling
– Thus for welding the pulse is usually longer than for drilling and shaped to have a smaller initial peak.
2. Joining efficiency is dependent on _____
a) spot size
d) surface conditions
Explanation: In the laser welding process:
• The joining efficiency is greatly affected by the mode of the laser beam
• True TEM00 modes provide highest joining efficiencies.
3. Which of the following has no effect on laser welding?
a) Plane of polarisation
b) Joint geometries
c) Shroud gas composition
Explanation: Polarization should have no effect on laser welding since the beam is absorbed inside a keyhole and hence it should be absorbed regardless of the plane of polarization unlike cutting.
4. In some cases, polarisation can affect _____
a) weld fusion zones
c) focal position
d) spot size
Explanation: Some second order events have been noted by Beyer et al. which show the effect of polarization;
– variation in penetration
– the weld fusion zones are also wider for the case of s-polarisation (perpendicular to the plane of incidence).
5. At slow speeds, the beam is absorbed by _____ effects.
a) the george clooney
b) inverse Bremsstrahlung
Explanation: At slow speeds the plasma absorption dominates and the beam is absorbed by inverse Bremsstrahlung effects in the keyhole generating a plasma. Acousto-optic effects can be seen in the nonlinear optics field. Bridgman effect is used in electricity.
6. _____ is advantageous for CO2 lasers.
a) High reflectivity
b) High absorptivity
c) Low reflectivity with short wave length
d) Low absorptivity with high wave length
Explanation: In welding with a conduction limited weld then the surface reflectivity becomes extremely important. The lower reflectivity with the shorter wavelengths gives a distinct advantage to Excimer, YAG or CO lasers over the CO2 laser.
7. The effect of welding speed can be seen on ____
a) weld bead
c) power consumption
Explanation: The effect of speed on the welding process is principally described by the
• Overall heat balance equation due to time for conduction
• Weld bead
• Shrouding high speed welds.
8. Which of the following is not affected by the speed of welding?
a) Pool size
b) Pool flow pattern
c) Weld bead
d) Focal position
Explanation: As the speed increases the pool flow pattern and size changes. At higher speeds, if the power is high enough and the pool large enough then undercut is produced which proceeds and edge freezing occurs leaving a slight undercut but the thread of the pool in the centre.
9. At slow speeds, smaller pool is formed.
Explanation: At slow speeds:
– the pool is large and wide and may result in drop out
– the ferrostatic head is too large for the surface tension to keep the pool in place and so it drops out of the weld leaving a hole or depression.
10. At high speeds, undercut occurs.
Explanation: At higher speeds:
– the strong flow towards the centre of the weld in the wake of the keyhole has no time to redistribute and is hence frozen as an undercut at the sides of the weld.
11. Which of the following lasers is suitable for welding of components made of aluminium?
a) Nd-YAG laser
b) Dye laser
c) Combination of CO and Excimer lasers
d) Combination of ruby and CO2 lasers
Explanation: An Excimer and CO2 laser beam combination showed improved coupling for the welding of high reflectivity materials, such as aluminium or copper could be obtained. Using two electron beams, the keyhole could be stabilized causing fewer waves on the weld pool and giving a better penetration and bead shape.
12. The improved coupling in case of welding of high reflectivity materials using twin beam lasers is due to _____
a) surface rippling
b) surface tension
c) surface smoothness
d) surface area
Explanation: The enhanced coupling was considered principally due to,
• altering the reflectivity by surface rippling caused by the Excimer
• a secondary effect coining from coupling through the Excimer generated plasma.
13. Which of the following is the problem on welding aluminium by laser welding?
c) Less grain growth
d) Brittle weld
Explanation: Following problems are faced while laser welding aluminium:
– High reflectivity
– Excessive fluidity.
14. Which of the following is the problem on welding heat resistant alloys by laser welding?
a) Brittle welds
b) Hot Cracking
d) High power consumption
Explanation: Following problems are faced while laser welding heat resistant alloys:
– Brittle welds
– Segregation problems
15. Which of the following materials faces the problem of hot cracking while laser welding?
a) Inco 718
d) Iridium alloys
Explanation: Problems faced during laser welding of materials like Inco718, Jetehet, M152, Hastelloy are-
– Weld is more brittle
– Segregation problems
While laser welding Iridium alloys, there are chances of hot cracking. Steels can be laser welded very easily without any problems.
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