CWI Welding Process Principles 3 — Questions and Answers
Question 1: What is the purpose of using a 'backing bar' in a groove weld?
- To preheat the base metal
- To support the molten weld pool and ensure complete root fusion (Correct answer)
- To measure joint gap
- To prevent distortion in the heat-affected zone
Correct answer: To support the molten weld pool and ensure complete root fusion
A backing bar (or backing strip) is placed behind the root of the joint to support the molten pool, prevent burn-through, and help achieve complete joint penetration.
Question 2: Which transfer mode in GMAW is generally associated with the highest heat input and is used for thick materials in the flat position?
- Short-circuit transfer
- Globular transfer
- Spray transfer (Correct answer)
- Pulse transfer
Correct answer: Spray transfer
Spray transfer operates at high voltage and current, producing a steady stream of fine droplets with high heat input, making it suitable for thick materials in the flat or horizontal position.
Question 3: In GTAW, what is the effect of using pure argon shielding gas on an aluminum weld?
- It increases penetration only
- It provides cathodic cleaning action that removes the oxide layer (Correct answer)
- It prevents any arc from forming
- It causes excessive spatter
Correct answer: It provides cathodic cleaning action that removes the oxide layer
When welding aluminum with GTAW using AC, the electrode-positive half-cycle provides a cathodic cleaning action that breaks up and removes the refractory aluminum oxide layer.
Question 4: What is 'arc blow' in SMAW, and when is it most commonly encountered?
- Excess shielding gas pressure; occurs with all electrodes
- Magnetic deflection of the arc; most common with DC on ferromagnetic materials near the end of a joint (Correct answer)
- Electrode overheating; occurs with large-diameter electrodes
- Flux gas bubbling; occurs at high travel speeds
Correct answer: Magnetic deflection of the arc; most common with DC on ferromagnetic materials near the end of a joint
Arc blow is caused by unbalanced magnetic fields in the workpiece deflecting the arc, and it most frequently occurs with DC welding on ferromagnetic steel, particularly near joint ends or heavy fixturing.
Question 5: Which welding process deposits filler metal using the resistance heating of a wire electrode fed into a molten slag pool?
- Electroslag welding (ESW) (Correct answer)
- Plasma arc welding (PAW)
- Flux-cored arc welding (FCAW)
- Stud welding
Correct answer: Electroslag welding (ESW)
Electroslag welding uses the electrical resistance of a molten slag pool to generate heat, melting both the consumable electrode and base metal as the weld progresses vertically.
Question 6: What is the function of the 'nozzle' in a GMAW gun?
- Feed the wire electrode to the contact tip
- Direct shielding gas around the weld zone (Correct answer)
- Sense arc voltage for feedback control
- Cool the contact tip during welding
Correct answer: Direct shielding gas around the weld zone
The nozzle directs and concentrates the shielding gas flow around the arc and weld pool to protect them from atmospheric contamination.
Question 7: A CWI observes that a GMAW weld has excessive porosity. Which process variable is MOST likely the primary cause?
- Incorrect travel angle
- Inadequate shielding gas coverage (Correct answer)
- Excessive preheat temperature
- Wrong contact-tip-to-work distance
Correct answer: Inadequate shielding gas coverage
Porosity in GMAW is most commonly caused by inadequate shielding gas coverage, allowing atmospheric nitrogen and oxygen to enter the weld pool and become entrapped as gas pores.
CWI Welding Process Principles 3
What is the purpose of using a 'backing bar' in a groove weld?