6 Common Problems with MIG Welding and How to Fix Them

By ced •  Updated: 08/22/22 •  5 min read

Welding occasionally involves human error and inaccuracy, as with most other processes. Welding defects are frequently a result of incorrect equipment settings, parameters, or techniques. As welders, we must be equipped with the knowledge necessary to address weld defects as soon as they arise.

In this article, we’ll discuss the most typical MIG welding defects, how to spot them, and how to fix or minimize them in the future.

Top 6 Most Common MIG Weld Defects and Effective Solutions to Fix Them

1. Undercut

Undercut happens when the weld becomes excessively wide, the base metal dives in at the edges due to incorrect welding technique, and insufficient filler material to cover the cavity, leaving us with a groove on the weld’s toes. It can be caused when the arc length is excessively long, there is a heat surplus, the travel speed is too fast, or the torch is angled in one direction for a long time.


Ensure maintaining a tighter arc, lowering the travel speed so that the joint gets filled adequately, and keeping the torch centered towards the joint’s middle segment.

2. Porosity

The primary reason for porosity is gas getting trapped inside the weld metal. Inappropriate shielding gas coverage is one of the principal causes of porosity. Some other factors include unclean base material, an excessively angled gun, and expanding the wire further away from the nozzle.


Inspect the flow meter first to ensure an appropriate gas flow, and adjust as applicable. If there are any drafts, close off the welding region and inspect the welding gun and gas hoses for leaks.

To guarantee optimum shielding gas coverage, it’s crucial to-

3. Cold lap and lack of fusion

In MIG welding, cold lap and lack of fusion can occur separately or simultaneously. The failure of the weld metal to completely fuse to the base metal or the last weld bead results in a lack of fusion. It’s typically caused due to inaccurate welding gun travel speed or angle. Inappropriate travel speeds can also lead to a cold lap, resulting in the weld overlapping on the weld’s toes by overfilling. 


We can prevent this issue by retaining a 0 to 15° gun angle while welding and positioning the arc on the forefront edge of the weld pool. Increasing travel speed is usually required to keep the optimum arc position. Fusion may also not occur in a weld when insufficient heat is supplied. Adjusting the voltage and ampere parameters or wire feed speeds can fix this issue.

4. Welding spatter

Spatter is the tiny metallic spherical structures that encircle a finished weld. When welding, the sparks that emerge from the welding torch or electrode frequently contain small pieces of molten metal; these are left behind after the weld has hardened. 

Excessive spatter can be caused by several complications with the MIG welding process, including:


To prevent significant spatter deposition, ensure that the shielding gas is flowing properly, cleanse the base materials properly, reduce the weld parameter specifications, and use a short stick out.

To reduce the possibility of spatter formation when welding self-shielded flux-cored wires, employ a drag technique and weld with straight polarity (electrode negative). Low voltage can also result in an excessive amount of spatter when utilizing flux-cored or metal-cored wires. Make any necessary voltage increases if splatter building up gets noticed.

5. Burn-through

Burn-through occurs when the weld metal entirely permeates the base material and is most prominent while welding thinner metals smaller than 1/8 inch in thickness or roughly 12 gauge. Extreme heat application is the primary cause of burn-through.


We can rectify this issue by lowering the wire feed speed or the voltage parameters. Also, raising the travel speed would come in handy, especially when MIG welding on metals sensitive to heat accumulation, such as thin aluminum.

6. Slag Inclusions

When a fragment of flux detaches and falls into the weld pool but does not melt out, it becomes entrapped and contaminates the weld as it hardens. It is known as a slag inclusion. Typically, a slag inclusion will expose the slag by leaving a fracture in the weld.

It results from the use of poor-quality electrodes, improper welding techniques, and failure to remove slag before the subsequent pass.


This issue can be prevented by storing the filler metals in a cool, sealed, and dry container, maintaining an appropriate arc length, and ensuring proper cleaning of slag between welds.

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When MIG welding defects, employing a structured methodology to diagnose each of them helps reduce the time, resources, and money investment in fixing them. Examine any welding-related characteristics that have altered, such as variables or welding technique, and then look at the above-discussed suggestions as possible solutions.

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