Module 2: MIG GMAW Operation Assessment Quiz

Module: U6M2 - MIG GMAW Operation Duration: 25 minutes Passing Score: 70% Format: Multiple choice and scenario-based

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In MIG welding, what does the wire feed speed control primarily determine?

The amperage (current) of the welding arc

The voltage of the welding arc

The shielding gas flow rate

The travel speed of the torch

Submit

Explanation: On most MIG welders, wire feed speed directly controls the amperage. Faster wire feed = more wire melting = more current drawn. The relationship is approximately linear. Voltage is controlled by a separate knob and determines arc length and bead shape.

What is the correct MIG welding polarity for solid wire (ER70S-6)?

DCEP (DC Electrode Positive) — wire is positive, workpiece is negative

DCEN (DC Electrode Negative)

AC (Alternating Current)

Polarity does not matter for MIG welding

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Explanation: DCEP (also called reverse polarity) directs approximately 70% of the arc heat to the wire and 30% to the workpiece, producing the best penetration and bead shape for solid MIG wire. DCEN is used for flux-cored wire. Wrong polarity causes poor penetration, excessive spatter, and an unstable arc.

What is the ideal MIG torch angle for a flat-position butt weld?

5°-15° push (forehand) angle from perpendicular in the direction of travel

45° angle from the workpiece surface

90° perpendicular to the surface at all times

30°-45° drag (backhand) angle

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Explanation: A slight push angle (5°-15° from perpendicular, torch tilted forward in the direction of travel) provides good gas coverage and visibility of the weld pool for flat-position butt welds. The push technique produces a wider, flatter bead with less penetration. A drag technique (pulling) gives more penetration but a narrower, taller bead.

A MIG welder is producing excessive spatter. Which parameter adjustment is most likely to fix it?

Increase the voltage slightly — the arc is too short (cold)

Increase the wire feed speed

Decrease the shielding gas flow

Switch to a larger wire diameter

Submit

Explanation: Excessive spatter is most commonly caused by voltage that is too low for the wire feed speed — the arc is too "cold" and the wire dips into the pool erratically. Increasing voltage lengthens the arc slightly and smooths the transfer. Other causes include: incorrect polarity, poor ground connection, or contaminated wire.

What is "short-circuit transfer" in MIG welding?

The wire touches the weld pool, creates a short circuit, and small drops of metal transfer — the most common mode for thin material

When the welding machine short circuits and shuts off

When the wire feed motor stalls

When the shielding gas runs out mid-weld

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Explanation: Short-circuit transfer occurs at lower voltage/wire feed settings. The wire alternately contacts the pool (short circuit — high current melts the wire tip) and separates (arc re-establishes). This cycle happens 20-200 times per second, producing the characteristic "bacon frying" sound. It is the most common mode for thin material and all-position welding.

What is the correct contact-tip-to-work distance (CTWD) for MIG welding?

⅜" to ½" (3/8" to 1/2") for short-circuit transfer

2" or more for maximum arc length

The nozzle should touch the workpiece

CTWD does not affect the weld

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Explanation: CTWD (stickout) affects the welding current and arc behavior. Too short: wire may fuse to the contact tip, excessive current. Too long: excessive resistance heating of wire, unstable arc, reduced shielding. The standard CTWD for short-circuit MIG is ⅜"–½". Increasing CTWD reduces effective amperage; decreasing it increases amperage.

When MIG welding a T-joint fillet weld, where should the arc be directed?

Into the root (corner) of the joint, with the torch bisecting the angle between the two pieces

Only at the horizontal plate

Only at the vertical plate

Above the joint, letting gravity pull the metal down

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Explanation: The torch should split the angle between the two plates (45° for a 90° T-joint), directing the arc into the root where both pieces meet. This ensures fusion to BOTH members. A common beginner mistake is pointing the torch at only one plate, resulting in lack of fusion on the other plate — a critical defect.

What causes "bird-nesting" (wire tangling) in the MIG gun cable?

Wire feed drive rolls pushing wire that cannot exit the torch — blocked tip, kinked liner, or too much tension

Using the wrong shielding gas

Welding too fast

The ground clamp being loose

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Explanation: When the wire cannot advance through the torch (blocked contact tip, kinked or worn liner, sharp bend in the cable), the drive rolls continue pushing, causing the wire to tangle into a "bird's nest" at the drive rolls. Prevention: keep the gun cable straight during welding, replace worn liners, use correct tip size, and do not set drive roll tension excessively high.

A student's MIG weld has inconsistent width — wide in some areas, narrow in others. What is the most likely cause?

Inconsistent travel speed — the student is moving the torch at varying speeds

The shielding gas is contaminated

The wire is the wrong diameter

The welding table is not level

Submit

Explanation: Bead width is directly controlled by travel speed (and secondarily by voltage). Inconsistent travel speed produces a bead that varies in width and height. This is the most common beginner issue. The fix is practice — maintain a steady, consistent push speed while watching the weld pool size rather than the arc.

What is the purpose of the MIG gun's diffuser/gas nozzle?

To direct shielding gas evenly around the arc and weld pool, protecting it from atmospheric contamination

To cool the contact tip

To focus the arc into a smaller point

To filter impurities from the shielding gas

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Explanation: The gas nozzle creates a laminar flow of shielding gas around the arc, forming an invisible protective cone that prevents oxygen and nitrogen from reaching the molten weld pool. If the nozzle is blocked with spatter, the gas flow becomes turbulent and shielding is compromised, causing porosity.

When should you use anti-spatter spray on the MIG nozzle?

Before welding, applied to the inside of the nozzle and contact tip area to prevent spatter adhesion

During welding, sprayed directly on the weld pool

After welding, to clean the finished weld

Never — anti-spatter spray causes contamination

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Explanation: A light coating of anti-spatter spray (or dip gel) on the inside of the nozzle before welding prevents spatter from adhering and blocking gas flow. It should be applied when the torch is cool and the machine is off. It should NEVER be sprayed on the workpiece or during active welding — it contains silicone which causes contamination and porosity.

A student notices porosity (small holes) in their MIG weld. Which of the following is NOT a likely cause?

The welding table is not grounded to earth ground

The shielding gas flow rate is too low

There is a draft or fan blowing across the weld area

The base metal has oil or paint on the surface

Submit

Explanation: Porosity is caused by gas trapped in the solidifying weld pool. Common causes include: insufficient shielding gas, gas blown away by drafts, contaminated base metal (oil, paint, moisture, rust), wet wire or filler, or a damaged gas hose/fitting allowing air to mix with shielding gas. The welding table's earth ground connection does not affect gas shielding or porosity.

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Last Updated: 2026-03-19