456A MIG/FCAW (GMAW & Flux-Cored Arc Welding) 4 — Questions and Answers
Question 1: What is the purpose of the contact tip in a GMAW gun?
- Transfers current to the wire and guides the wire accurately to the arc (Correct answer)
- Directs shielding gas flow around the arc
- Controls wire feed speed at the gun
- Prevents the wire from melting back into the gun liner
Correct answer: Transfers current to the wire and guides the wire accurately to the arc
The contact tip (made of copper alloy) transfers welding current from the gun body to the electrode wire through electrical contact as the wire slides through it. It also guides the wire accurately toward the weld joint. Contact tips must match the wire diameter and should be replaced when worn oval or spattered shut.
Question 2: What is 'cold wire inclusions' or 'cold laps' in FCAW welding and how are they prevented?
- Unmelted wire tips fused onto the weld surface; prevented by proper voltage and maintaining correct torch angle (Correct answer)
- Flux particles trapped under the weld bead; prevented by faster travel speed
- Gas pockets from insufficient shielding; prevented by increasing flow rate
- Cracks from thermal cycling; prevented by controlled cooling
Correct answer: Unmelted wire tips fused onto the weld surface; prevented by proper voltage and maintaining correct torch angle
Cold wire inclusions occur when the wire tip is not fully melted before contacting the weld pool or base metal, leaving an unmelted wire stub. Proper voltage settings ensure the wire melts completely in the arc. Torch angle must keep the arc in the leading edge of the pool.
Question 3: What is the recommended technique for welding a vertical-up fillet weld with GMAW short-circuit transfer?
- Triangular or Z-weave pattern with pauses at the toes to build up metal and prevent sagging (Correct answer)
- Stringer bead dragged downward from top to bottom
- Circular weave motion with continuous forward travel
- Push technique with 30° torch angle pointing upward
Correct answer: Triangular or Z-weave pattern with pauses at the toes to build up metal and prevent sagging
Vertical-up GMAW (short-circuit) typically uses a triangular or Z-weave pattern. Pausing slightly at each toe ensures fusion to the base metal and builds up the weld profile. The upward travel direction allows gravity to support the solidifying weld pool and prevents undercutting.
Question 4: What is the difference between E70T-1 and E71T-1 FCAW electrodes?
- E70T-1 is limited to flat/horizontal positions; E71T-1 is all-position including vertical-up and overhead (Correct answer)
- E70T-1 is self-shielded; E71T-1 requires external shielding gas
- E70T-1 has higher tensile strength than E71T-1
- E70T-1 uses CO2 gas; E71T-1 uses Argon
Correct answer: E70T-1 is limited to flat/horizontal positions; E71T-1 is all-position including vertical-up and overhead
In the FCAW electrode classification, the digit after 'E7' indicates position: '0' means flat and horizontal only, '1' means all positions. E70T-1 is a flat/horizontal electrode producing a large, fluid slag; E71T-1 has a fast-freezing slag system designed for out-of-position welding.
Question 5: What does 'nozzle-to-work distance' (also called contact-tip-to-work distance or stick-out) affect in FCAW?
- Resistance preheating of the wire, affecting current draw, deposition rate, and penetration (Correct answer)
- Shielding gas coverage area and nozzle clogging rate only
- Wire feed speed at the drive rolls
- Duty cycle of the welding machine
Correct answer: Resistance preheating of the wire, affecting current draw, deposition rate, and penetration
In FCAW, as in GMAW, the wire stick-out distance affects the resistive preheating of the wire between the contact tip and the arc. Longer stick-out preheats the wire more, reduces actual welding current (at the same wire feed speed), and lowers penetration. It is a critical variable specified in the WPS.
Question 6: Under CSA W59, what inspection requirement applies to completed FCAW welds on Category C (dynamically loaded) structures?
- Visual inspection plus non-destructive testing (NDT) as specified; radiographic or ultrasonic testing of groove welds (Correct answer)
- Visual inspection only is required for all weld categories
- Magnetic particle testing of all fillet welds
- Dye penetrant testing of every weld pass
Correct answer: Visual inspection plus non-destructive testing (NDT) as specified; radiographic or ultrasonic testing of groove welds
CSA W59 categorizes structures by loading type. Category C (dynamically loaded) structures require enhanced inspection including NDT (RT or UT) of complete joint penetration groove welds in addition to mandatory visual inspection. The inspection level reflects the higher consequences of weld failure under cyclic loading.
456A MIG/FCAW (GMAW & Flux-Cored Arc Welding) 4
What is the purpose of the contact tip in a GMAW gun?