This set of Advanced Manufacturing Processes Questions and Answers focuses on “Laser Welding – 5”.
1. In keyhole mode of laser welding, hole is stabilized by the _____
a) weld puddle
b) shielding gases
c) pressure of the vapour
d) laser beam
View Answer
Explanation: In “keyhole” welding in which there is sufficient energy/unit length to cause evaporation and hence a hole in the melt pool. This hole is stabilized by the pressure from the vapour being generated.
2. In keyhole mode of laser welding, the keyhole behaves like _____
a) optical black body
b) an energy reflector
c) an energy amplifier
d) a shielding
View Answer
Explanation: The “keyhole” behaves like an optical black body in that the radiation enters the hole and is subject to multiple reflections before being able to escape. Nearly all the beam energy is absorbed once the keyhole is formed.
3. Which of the following has the highest joining efficiency?
a) Acetylene flame welding
b) TIG welding
c) Electron beam welding
d) Laser welding
View Answer
Explanation: The joining efficiencies for different welding processes is listed below;
Oxy-acetylene flame welding — 0.2-0.5
Manual arc welding – 2-3
TIG welding – 0.8-2
Electron beam welding – 20-30
Laser beam welding – 15-25.
4. Flow structures can directly affect the ____
a) laser wave formation
b) frozen bead
c) weld puddle
d) porosity
View Answer
Explanation: The two principle areas of interest in laser beam welding are;
– Flow structures which directly affects the wave formation in the weld pool and frozen bead geometry
– Absorption mechanism
• Fresnel absorption (absorption during reflection from surface)
• Inverse Bremmstrahlung, leading to plasma re-radiation.
5. During laser welding, any hump on the surface can cause _____
a) increase in weld porosity
b) flow instability
c) higher energy absorption
d) decrease in the weld thickness
View Answer
Explanation: Any hump on the surface will cause localized higher absorption and an explosion due to instantaneous evaporation. The keyhole walls are fluctuating with flow velocities up to 0.4 m/s.
6. The hot plasma vapour emerging from the keyhole may ionize _____
a) shielding gas
b) shroud gas
c) lasing material
d) workpiece material
View Answer
Explanation: The keyhole contains considerable metal vapour, which is partially absorbing and hence capable of forming a plasma on further heating. This hot plasma vapour emerging from the keyhole may ionize the shroud gas. Ionized gas has free electrons and is thus capable of absorbing or even blocking the beam.
7. How many of the following process parameters can affect the welding process?
• Power pulses
• Wavelength
• Gap
• Joint geometries
a) 1
b) 2
c) 3
d) 4
View Answer
Explanation: Following are the parameters that can affect the welding process:
• Beam Properties:
– Power, pulsed or continuous
– Spot size and mode
– Polarisation – Wavelength
• Transport Properties:
– Speed
– Focal position
– Joint geometries
– Gap tolerance.
8. Which of the following does not affect the operating characteristics in laser welding?
a) shroud gas composition
b) material surface conditions
c) component orientation
d) shroud design
View Answer
Explanation: Following are the parameters that can affect the welding process:
• Shroud/shielding Gas Properties:
– Composition
– Shroud design
– Pressure/velocity
• Material Properties:
– Composition
– Surface condition.
9. The maximum welding speed varies directly with the power
a) True
b) False
View Answer
Explanation: The maximum welding speed for a given thickness rises with an increase in power. The fall off shown at the higher power levels of 2kW could be attributed to the poorer mode structure given by most lasers when working at their peak power.
10. Pulse repletion factor is considered while determining the welding speed.
a) True
b) False
View Answer
Explanation: The use of pulsed power allows two more variables:
– pulse repetition frequency (PRF),
– % overlap to be considered.
The welding speed is decided by the following relation:
– spot size x PRF x (1% overlap).
Sanfoundry Global Education & Learning Series – Manufacturing Processes.
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