WCL Welding Processes & Techniques 5 — Questions and Answers
Question 1: What is 'spray transfer' in GMAW, and what shielding gas is required for it?
- Large droplet transfer using 100% CO2
- A stream of fine droplets axially transferred across the arc, requiring at least 80% argon in the shielding gas (Correct answer)
- Wire-to-puddle contact transfer with pure helium shielding
- Pulsed droplet transfer using 100% argon at any amperage
Correct answer: A stream of fine droplets axially transferred across the arc, requiring at least 80% argon in the shielding gas
Spray transfer produces a smooth stream of fine droplets across the arc and requires a shielding gas with at least 80% argon to achieve the transition current threshold.
Question 2: Which document governs qualification of welding procedures and welders for most structural steel work in the US?
- ASME Section IX
- AWS D1.1 Structural Welding Code — Steel (Correct answer)
- API 1104
- NFPA 51B
Correct answer: AWS D1.1 Structural Welding Code — Steel
AWS D1.1 is the primary structural welding code for steel in the US, governing WPS qualification, welder qualification, and inspection requirements.
Question 3: What does 'PWHT' stand for, and what is its primary purpose in welding?
- Pre-Weld Heat Treatment; removes moisture before welding
- Post-Weld Heat Treatment; relieves residual stresses and tempers the HAZ after welding (Correct answer)
- Pulse-Width Heat Transfer; controls heat input during GMAW
- Pre-Weld Hardness Test; verifies base metal properties
Correct answer: Post-Weld Heat Treatment; relieves residual stresses and tempers the HAZ after welding
PWHT (Post-Weld Heat Treatment) involves controlled heating and cooling of the completed weld to relieve residual stresses and improve HAZ toughness.
Question 4: In SMAW, what does the last two digits of an electrode classification (e.g., E7018) indicate?
- Tensile strength in ksi
- The type of coating and usable welding current (Correct answer)
- The maximum thickness of base metal
- The diameter of the electrode in millimeters
Correct answer: The type of coating and usable welding current
The last two digits of an SMAW electrode classification indicate the type of flux coating and the compatible welding current (AC, DC+, DC-).
Question 5: What is the purpose of a 'root opening' (root gap) in a groove weld joint?
- To reduce the amount of filler metal needed
- To allow access for the root pass to achieve complete joint penetration (Correct answer)
- To prevent the backing bar from sticking to the weld
- To provide space for the flux during SAW welding
Correct answer: To allow access for the root pass to achieve complete joint penetration
The root opening provides space at the bottom of the groove so the welder can achieve complete joint penetration with the root pass.
Question 6: Which discontinuity is most likely to occur when welding dissimilar metals with significantly different thermal expansion coefficients?
- Porosity
- Tungsten inclusions
- Cracking due to thermal stress mismatch (Correct answer)
- Undercut along the weld toe
Correct answer: Cracking due to thermal stress mismatch
When dissimilar metals with different expansion rates are joined, differential thermal movement during heating and cooling creates stresses that can lead to cracking.
Question 7: What is the function of the 'contactor' in a GMAW welding gun circuit?
- It controls shielding gas flow rate
- It energizes the wire electrode only when the trigger is pulled, preventing accidental contact with live wire (Correct answer)
- It sets the wire feed speed electronically
- It monitors arc voltage and adjusts power output
Correct answer: It energizes the wire electrode only when the trigger is pulled, preventing accidental contact with live wire
The contactor is a safety switch that energizes the wire electrode only when the trigger is depressed, preventing the wire from being live when not welding.
WCL Welding Processes & Techniques 5
What is 'spray transfer' in GMAW, and what shielding gas is required for it?