Guide to Correcting GMAW Welding Defects

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There are several common GMAW welding defects (MIG) including:

Aluminum welds usually pose more problems than when working with steel since aluminum is a better conductor of heat and a lower melting point. This combination exposes aluminum welding projects to problems such as burn-through and warping.

Also, unlike steel which can be welded using a dragging or pushing technique, with aluminum the gun can only be dragged (also called backhand technique).

Voltage Related GMAW Welding Defect in Steel
GMAW welding defect caused by low voltage. Causes problem arc starting, lack of penetration and poor control. Other problems related to low voltage are convex bead profile, too much splatter and a low quality tie in at the weld toes.

GMAW Weld Testing With Solid-core Wire

Solid-core wires come in different types, with some preferred for oxygen gas shielding and others for a combination of Oxygen and Argon.

GMAW sold-core wire is primarily used in the steel welding of buildings, cars, motorcycles, containers, train rolling stock and construction machinery. They create reduced levels of slag, making it idea for multi-pass welding.

Normal Bead and Defective Weld Humping Bead
Normal GMAW Bead (Top) and what is called a Humping Bead (bottom). Caused by excessive speed when using a solid wire.


Lack of Penetration

Lack of input in the weld area. This can be penetration is the result of too little heat corrected by:

  1. Increasing the wire-feed speed and reducing the stick-out distance.
  2. Reducing the speed of travel.
  3. Using proper welding techniques.

Excessive Penetration

Excessive penetration usually causes burn through. It is the result of too much heat in the weld area. This can be corrected by:

  1. Reducing the wire-feed speed and increasing the speed of travel.
  2. Making sure that the root opening and root face are correct.
  3. Increasing the stick-out distance during welding and weaving the gun.

Weld Profiles at Different Speeds

Weld Profile Welding Speed (cm/min)
weld profile speed 25cm / min 25
weld profile speed 50cm-min 50
weld profile speed 75cm-min 75
weld profile speed 100cm-min 100

Use of solid wire, the table shows the effect of different welding speeds on the welding profile.


Whiskers are short lengths of electrode wire sticking through the weld on the root side of the joint. They are caused by pushing the electrode wire past the leading edge of the weld pool. Whiskers can be prevented by:

  1. Reducing the wire-feed speed and the speed of travel.
  2. Increasing the stick-out distance and weaving the gun.


Voids are sometimes referred to as wagon tracks because of their resemblance to ruts in a dirt road. They may be continued along both sides of the weld deposit. They are found in multi-pass welding. Voids can be prevented by:

  1. Avoiding a large contoured crown and undercut.
  2. Making sure that all edges are filled in.
  3. On succeeding passes, using slightly higher arc voltage and increasing travel speed.

Lack of Fusion

Lack of fusion also referred to as cold lap, is largely the result of improper torch handling, low heat, and higher speed travel. It is important that the arc be directed at the leading edge of the puddle. To prevent this defect, give careful consideration to the following:

  1. Direct the arc so that it covers all areas of the joint. The arc, not the puddle, should do the fusing.
  2. Keep the electrode at the leading edge of the puddle.
  3. Reduce the size of the puddle as necessary by reducing either the travel speed or wire-feed speed.
  4. Check current values carefully.


GMAW Welding Defect - Porosity
Porosity or pinholes in a weld on steel caused by inadequate use of shielding gas.

The most common defect in welds produced by any welding process is porosity. Porosity that exists on the face of the weld is readily detected, but porosity in the weld metal below the surface must be determined by x-ray or other testing methods. The causes of most porosity are:

  1. Contamination by the atmosphere and other materials such as oil, dirt, rust, and paint.
  2. Changes in the physical qualities of the filler wire due to excessive current.
  3. Entrapment of the gas evolved during weld metal solidification.
  4. Loss of shielding gas because of too fast travel.
  5. Shielding gas flow rate too low, not providing full protection or drawing air into the arc area
  6. Wrong type of shielding gas being used.
  7. Gas shield blown away by wind or drafts.
  8. Defects in the gas system.
  9. Improper welding technique, excessive stick-out, improper torch angle, and too fast removal of the gun and the shielding gas at the end of the weld.
Aluminum Weld Porosity
Weld where oxide wasn’t removed prior to weld. Using a drag (instead of push) welding technique contributing cause. If weld were cut open pinholes or porosity would be revealed.


Spatter is made up of very fine particles of metal on the plate surface adjoining the weld area. It is usually caused by high current, a long arc, an irregular and unstable arc, improper shielding gas, or a clogged nozzle.

Welding defects due to high voltage:

Welding Defects Due to High Voltage
High voltage causes poor arc control, poor and inconsistent weld penetration.

Irregular Weld Shape

Irregular welds include those that are too wide or too narrow, those that have an excessively convex or concave surface, and those that have coarse, irregular ripples. Such characteristics may be caused by poor torch manipulation, a speed of travel that is too slow, current that is too high or low, improper arc voltage, improper stick out, or improper shielding gas.


Undercutting is a cutting away of the base material along the edge of the weld. It may be present in the cover pass weld bead or in multi-pass welding. This condition is usually the result of high current, high voltage, excessive travel speed, low wire-feed speed, poor torch technique, improper gas shielding or the wrong filler wire. To correct undercutting, move the gun from side to side in the joint. Hesitate at each side before returning to the opposite side.

GMAW With Flux-cored Wire (FCW)

There are fundamentally three types of flux-cored wire:

  • rutile: rutile based flux. Known for usability.
  • basic: contain lime-flouride flux. Known for resistance to cracks.
  • metal: contains metal powder that becomes part of the weld, causing some slag cover

The performance and quality of the weld starts with picking the best welding wire for a particular job. Tables provided by manufacturers are rules of thumb and not absolute.


Defect due to high amperage and wire feed speed:

Defect Due to High Amperage and Wire Feed Speed
When the amperage is set higher than required or if the wire speed is too fast, problems such as poor arc starts, distortion, burn through and a wide weld bead can occur.

Burn-through may be caused by the following:

  1. Current too high.
  2. Excessive gap between plates.
  3. Travel speed too s1ow.
  4. Bevel angle too large.
  5. Nose too small.
  6. Wire size too small.
  7. Insufficient metal hold-down or clamping.

Defect due to low amperage and slower than required wire feed speed:

Defect Due to Low Amperage and Slower Than Required Wire Feed Speed
When the amperage is set lower than required or if the wire speed is too slow, problems such as poor tie-in at the toes and a convex bead can occur.

Crown Too High or Too Low

The crown of the weld may be incorrect due to the following:

  1. Current too high or low.
  2. Voltage too high or low.
  3. Travel speed too high.
  4. Improper weld backing.
  5. Improper spacing in welds with backing.
  6. Workpiece not level.

Penetration Too Deep to Too Shallow

Defect due to slow travel speed:

Defect Due to Slow Travel Speed
Slow weld travel speed can contribute to gmaw welding defects such as a large weld and burn through.

Incorrect penetration may be caused by any of the following GMAW welding defects:

  1. Current too high or low.
  2. Voltage too high or low.
  3. Improper gap between plates.
  4. Improper wire size.
  5. Travel speed too slow or fast.

Porosity and Gas Pockets

These GMAW welding defects may be the results of any of the following:

  1. Flux too shallow.
  2. Improper cleaning.
  3. Contaminated weld backing.
  4. Improper fit-up in welds with manual backing.
  5. Insufficient penetration in double welds.

Reinforcement Narrow and Steep-Sloped (Pointed)

Narrow and pointed reinforcements may be caused by the following GMAW welding defects:

  1. Insufficient width of flux.
  2. Voltage too low.

Mountain Range Reinforcement

If the reinforcement is ragged, the flux was too deep.

Defect due to fast weld travel speed:

Defect Due To Fast Weld Travel Speed
Fast travel speed can cause a narrow convex weld bead and poor tie-in at the weld toes. Can also cause inadequate weld penetration and inconsistency in the bead.


Undercutting GMAW welding defects may be caused by any of the following:

  1. Travel speed too high.
  2. Improper wire position (fillet welding).
  3. Improper weld backing.

Voids and Cracks

These weld deficiencies may be caused by any of the following:

  1. Improper cooling.
  2. Failure to preheat.
  3. Improper fit-up.
  4. Concave reinforcement (fillet weld).
About Jeff Grill

Jeff Grill hails from Long Island, a 118 mile stretch of land that starts just off the coast of Manhattan and stretches deep into the Atlantic ocean. He has always been interested in welding from an early age and has the cuts and bruises to prove it as he set out to work with a variety of metals.

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