CWI Welding Process Principles 4 — Questions and Answers
Question 1: What distinguishes flux-cored arc welding (FCAW-S) 'self-shielded' from FCAW-G 'gas-shielded'?
- FCAW-S uses a solid wire; FCAW-G uses a tubular wire
- FCAW-S generates its own shielding from the flux core without external gas; FCAW-G requires an external shielding gas (Correct answer)
- FCAW-S is always performed with AC; FCAW-G uses DC only
- FCAW-S cannot be used outdoors; FCAW-G is preferred outdoors
Correct answer: FCAW-S generates its own shielding from the flux core without external gas; FCAW-G requires an external shielding gas
FCAW-S electrodes contain compounds in the core that produce sufficient shielding gases and slag when decomposed, eliminating the need for an external gas supply, making it better suited for outdoor/field welding.
Question 2: In resistance spot welding, the weld nugget forms primarily due to:
- Arc heat between the electrodes and workpiece
- Resistance heating at the faying surfaces between the workpieces (Correct answer)
- Friction between the workpieces under pressure
- Induction heating from the electrode tips
Correct answer: Resistance heating at the faying surfaces between the workpieces
Heat is generated by the electrical resistance at the faying (contact) surfaces between the workpieces; combined with electrode force, this melts the base metal to form the nugget.
Question 3: What is the purpose of 'preheating' before welding high-carbon or alloy steels?
- Increase tensile strength of the weld
- Reduce the cooling rate to minimize hydrogen cracking and hard HAZ formation (Correct answer)
- Remove mill scale from the base metal surface
- Increase travel speed during welding
Correct answer: Reduce the cooling rate to minimize hydrogen cracking and hard HAZ formation
Preheat slows the cooling rate of the weld and heat-affected zone, reducing the risk of hydrogen-induced cracking and the formation of brittle martensite in hardenable steels.
Question 4: Which of the following is a characteristic feature of laser beam welding (LBW)?
- Very low power density requiring multiple passes
- Extremely high power density producing a narrow, deep weld with minimal heat input (Correct answer)
- Requires consumable electrodes for shielding
- Limited to welding ferrous metals only
Correct answer: Extremely high power density producing a narrow, deep weld with minimal heat input
LBW focuses an extremely high power-density beam onto a small spot, enabling deep, narrow welds with a very small heat-affected zone and minimal distortion.
Question 5: A welder is producing a multipass groove weld. Between passes, the inspector requires the welder to remove slag. Why is inter-pass slag removal critical?
- Slag removal preheats the weld for the next pass
- Slag inclusions will form if slag is not removed before depositing the next pass (Correct answer)
- Slag acts as a flux for subsequent passes and must be repositioned
- It prevents warping of the base metal
Correct answer: Slag inclusions will form if slag is not removed before depositing the next pass
If slag is not completely removed between passes, it can become entrapped in subsequent weld beads, creating slag inclusion discontinuities that reduce weld integrity.
Question 6: In oxyfuel gas welding (OFW), a 'carburizing' flame is identified by:
- A sharp, well-defined inner cone with no outer envelope
- An excess acetylene feather visible beyond the inner cone (Correct answer)
- A large, soft, luminous blue flame
- A very short, harsh inner cone with a hissing sound
Correct answer: An excess acetylene feather visible beyond the inner cone
A carburizing (reducing) flame has excess acetylene, producing a visible intermediate feather or acetylene cone between the inner cone and the outer envelope.
Question 7: What is 'interpass temperature' and why is it controlled in welding procedures?
- The temperature of the shielding gas; controlled to maintain arc stability
- The temperature of the weld and base metal before depositing a subsequent pass; controlled to limit heat input and maintain mechanical properties (Correct answer)
- The electrode tip temperature; kept below the melting point of flux
- The ambient temperature of the welding environment; monitored for OSHA compliance
Correct answer: The temperature of the weld and base metal before depositing a subsequent pass; controlled to limit heat input and maintain mechanical properties
Interpass temperature is the temperature measured in the weld zone immediately before welding the next pass; exceeding the maximum can over-temper the HAZ and reduce toughness or strength.
CWI Welding Process Principles 4
What distinguishes flux-cored arc welding (FCAW-S) 'self-shielded' from FCAW-G 'gas-shielded'?