I-CAR Welding Techniques and Processes 2 — Questions and Answers
Question 1: What is the correct sequence for performing a MIG plug weld on a structural panel?
- Weld around the perimeter of the hole, then fill the center (Correct answer)
- Fill the center of the hole first with a single pass
- Tack the edges, grind, then fill
- Start at the center and weld in a circular outward motion
Correct answer: Weld around the perimeter of the hole, then fill the center
Starting around the perimeter ensures fusion to the lower panel before filling the center, producing a consistent nugget that mimics a factory spot weld.
Question 2: When using STRSW equipment, what parameter most directly determines weld nugget size?
- Electrode tip diameter (Correct answer)
- Weld current (amperage)
- Electrode force (squeeze pressure)
- Weld time (cycles)
Correct answer: Electrode tip diameter
The diameter of the electrode tip directly governs the contact area and thus the diameter of the resistance spot weld nugget produced.
Question 3: What is a 'destructive weld test' used to verify in collision repair?
- That the welding machine is calibrated correctly
- That the weld settings produce a weld nugget of adequate size and penetration on scrap metal (Correct answer)
- That the repaired panel has correct dimensions
- That shielding gas flow rate is set properly
Correct answer: That the weld settings produce a weld nugget of adequate size and penetration on scrap metal
A destructive weld test on scrap material confirms that current settings produce welds with proper nugget size and fusion before the same settings are applied to the vehicle.
Question 4: Which type of weld joint is most commonly used when installing a sectioned structural rail?
- Lap weld joint
- Butt weld joint with backing (Correct answer)
- T-weld joint
- Edge weld joint
Correct answer: Butt weld joint with backing
A butt weld with a backing strip or backing support is preferred for sectioning structural rails because it provides full penetration and strength equivalent to the original joint.
Question 5: Why must aluminum welding use a dedicated MIG welder or torch liner, separate from steel equipment?
- Aluminum requires a different shielding gas regulator
- Steel contamination from shared liners causes porosity and weld defects in aluminum (Correct answer)
- Aluminum cannot be welded with MIG at all
- The wire feed speed is different for aluminum
Correct answer: Steel contamination from shared liners causes porosity and weld defects in aluminum
Steel particles left in a shared liner contaminate aluminum welds, causing porosity, inclusions, and dramatically weakened joints.
Question 6: What does 'wire feed speed' control in a MIG welding setup?
- The voltage of the arc
- The travel speed of the welder
- The rate at which filler wire is delivered to the weld pool, which determines amperage (Correct answer)
- The flow rate of shielding gas
Correct answer: The rate at which filler wire is delivered to the weld pool, which determines amperage
Wire feed speed determines how fast filler metal enters the arc, which directly controls the welding amperage and heat input.
Question 7: Which weld defect appears as small holes or voids within the weld bead and is often caused by contamination or inadequate shielding gas?
- Undercut
- Porosity (Correct answer)
- Cold lap
- Overlap
Correct answer: Porosity
Porosity consists of gas pockets trapped in the solidified weld metal, typically caused by contamination, moisture, or insufficient shielding gas coverage.
I-CAR Welding Techniques and Processes 2
What is the correct sequence for performing a MIG plug weld on a structural panel?