12 Common MIG Welding Issues And How To Troubleshoot

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Some of the most common issues with welding come down to three things:

  • Dirty workspace or materials
  • Poor quality welding tips or fillers
  • Too high or too low voltage and amperage

But, there are certainly more reasons why your weld is not coming out the way you intended. This article will help you to identify and troubleshoot some of the most common MIG welding issues. Whether you are having issues with wire feed, splatter, or penetration, this will cover it all. 


Sometimes, small pockets of gas can get trapped in the weld metal. This is called porosity. Porosity can occur internally or externally and can weaken the weld. Is a common issue among welders, and can be caused by several things.

First, porosity can be caused by poor gas coverage. The welding process requires a certain amount of shielding gas to prevent weld puddles from air penetration. Too much gas flow can pull air into the weld, causing porosity. Too little gas coverage can also cause porosity in your welds. Try to weld with 50-60 CFH of gas flow to prevent this.

Porosity can also be caused by surface contaminants. Dirt, oil, rust, paint, and even sweat can cause porosity in your weld. To prevent this, clean your wire, hose, welding surface, and gloves before going to work. To clean these, you can use metal grinders like steel wool, or chemical solvents.

Porosity can be caused by several things, but these two are the most common. If you have a porous weld, it is best to grind off your porous welds and start again, this time making sure that there is no surface moisture, no contaminants, and proper flow of shielding gas.

Issues With Fusion

One of the main things that cause a lack of fusion is temperature. If there is not enough voltage, your gun will not be hot enough for a sufficient weld. Sometimes it may even appear to be a good weld, but because there was not enough amperage, the weld is not strong. 

Lack of fusion can also be caused by technique. If the edges of your materials are not aligned properly, fusion can be an issue. Slots in your beads could also be the cause of a poorly fused weld. Be sure to align your beads correctly for the strongest possible weld. Gun angle can also play a part in this, so make sure your technique is correct.

Magnetic arc blow also causes poor fusion. This is when the magnetic field around the metals is distorted and is usually caused by the arc current. To prevent this, it is important to demagnetize the metal before you begin. You may also readjust your current return cable clamps to more stable positions.

Unclean surfaces can also cause poor fusion. If surfaces have traces of rust, oil, or dirt, these particles will prevent a full, molecular weld. It is good policy to make sure that all of your surfaces and tools are clean before you begin to weld.

Issues With Wire Feed

Wire feed problems are typically due to equipment issues and can be caused by:

  • Poor wire quality
  • Worn out drive rolls
  • Birdnesting of the wire
  • Old, defective guns 

If you are having this issue, first check the quality of your wire. It may have rusted over time. Rusty wire welds differently because it has already been oxidized. If you notice rust on the wire you are using, feed it through your gun until you reach the clean wire. When not in use, store your wire in a place where it is not exposed to the elements.

Drive rolls need to be replaced regularly. You will know that a drive roll needs to be replaced when you have to tighten it much more than you used to, to hold the wire in place. If your wire looks fine, then the issue likely is within your drive rolls or liner. Issues with liners are caused by dirt, clogging, or kinking. 

If you are still having a poor wire delivery, it might be time to replace your gun. Copper wires inside of your welding gun wear down over time and need to be inspected regularly. You can tell when a gun needs to be replaced because certain parts of the gun will be much hotter than usual/how it used to be.

Welding Spatter

Spatter is a given with MIG welding. It is bound to happen. But there are a few things you can do to help prevent excess spatter. 

First, check the amperage and voltage of your machine. If your amperage is too high, your wire may be feeding too quickly and causing excess spatter. A voltage that is too high or too low can also cause spattering. Make sure that your amperage and voltage are finely tuned to your machine and project, and do not be afraid to do test welds.

Make sure that you are using the shortest wire stick-out allowed for MIG welding. If your wire sticks out too far, this can cause splatter. It is important to use the right-sized contact tips and to have clean liners to prevent this issue as well. 

The transfer technique you are using to weld may also be causing excess splatter. Globular and short arc techniques cause the most splatter, while spray transfer causes less. Spray transfer allows for higher arc stability, and therefore less splatter. Try out different transferring techniques to see which is best for your project and equipment.

Irregular Weld Shape

If your beads are not laying flat against the weld, there is likely an issue with heat input or technique. Ropy-looking or convexed beads are probably caused by heat settings that are too low for the thickness of the metal being welded. 

To solve this, make sure to read through the manual of your welding tools to see which voltage and amperage work best for your tools and projects. As different tools have different amperage and voltage needs, this will vary from machine to machine.

Another issue that causes your beads to convex or concave is your technique. Pushing your gun along, (also called a forehand technique) will help you to have flatter and more consistent welds. Most welding resources recommend that you keep your application angle at 5-10 degrees, for best results. 

Improper weld shape can also be caused by the speed of welding. If you go too fast, it can come out ripply and uneven. Also, make sure that you are applying the right amount of shielding gas. Improper shielding gas can have many unintended consequences that require a lot of extra effort to fix. It is best to check all of your settings before you start.


Weld distortion occurs during the cooling process of the weld. Distortion affects the stability of the weld, and it is important to try to actively combat this before and while you are welding.

The best way to combat shrinkage and distortion is to weld from the center out, or by alternating ends. If you start with one end and continue in a line, your weld will likely become distorted as you go. It is also important to secure your two surfaces with clamps before you begin. You do not want it to move while you go.

Shrinkage and distortion can also be combated by welding quickly. If you weld slowly, the material becomes hotter and the welds can slip and skew out of place. It is also important to not over-weld. Excessive welding can cause the width of the weld to thicken, not the height. If the width is excessively thick, distortion will occur while drying.

Other ways to minimize distortion are:

  • Use intermittent welding
  • Do not pass over the weld too many times
  • Use strongbacks
  • Distribute welding heat evenly
  • Preheat material before you begin


Undercuts occur when a weld’s edges have “cut” into the parent material. They usually occur near the toe of the weld. Undercuts weaken the weld and look bad. They cause an indentation in the weld and oftentimes this is not permissible by weld inspectors. Oftentimes, undercuts are caused because of a lack of gaps between materials.

As with most welding issues, undercuts are mainly caused by amperage or voltage problems. If you are having issues with undercuts, your voltage and amperage are likely too high. When these are too high, the parent metal is cut into and melted, making the weld less strong. Undercut can also be caused by holding an arc for too long. 

Using the correct weaving technique will also help to prevent undercut. Weaving is used to regulate the heat while welding, and if you weave too quickly, it is likely that an undercut will occur. If you weld too quickly, the base metal can melt. It is best to go at a nice steady pace; not too slow or fast. Slow welding holds a bunch of issues on its own.

Your use and size of electrodes can cause undercut issues. If excessive heat is applied to the edges of your materials, undercuts will likely occur. Also, be sure that you are using the right size electrode for the job, as an oversized electrode can cause more melting than you have intended for.

Excessive/Insufficient Penetration

Excessive penetration occurs when the welding material has melted through the base material, causing the excess to bevel below the weld. If this is an issue for you, you are likely using too high of amperage, too high of wire feed speed. 

You may also be spending too much time on each weld, causing the base material to melt. To fix this, increase the voltage of your welder and decrease the amperage. It is also important to remember that, as contact tip to work distance increases, penetration decreases. So make sure you are holding your tip far enough away from the weld.

Insufficient penetration is just as much of a problem as is excessive penetration. Insufficient penetration occurs when heat input is too low, and the weld does not completely cover the gaps between two materials. 

Counterintuitively, increasing the voltage on your welder will not increase penetration. Increasing amperage will, but not voltage. So, to combat insufficient penetration, you will need to lower your voltage and increase the weld feed speed. 

MIG Welder Has Stopped Working

If your welder stops working or is stuttering or having issues, there are a number of things you can check that might end up leading you to the problem.

  • Power Input: If your welder is not arcing, you may have an issue with the power input. The outlet you use should be around 110V-120V. Your welder may have stopped working because of insufficient power, or an inability for power to reach your machine.
  • Clogging/Contamination: A lack of arc in your welder can be caused by its consumable parts. If parts of your welder are clogged, it will not work, no matter how insignificant you think the debris may be. Be sure to change your liners regularly and weld on clean surfaces always.
  • Hot Electrode Holder: If your electrode holder heats up, there may be a connection issue. Check to make sure that connections are as tight as they should be. You may also have the wrong size holder, causing it to not arc.
  • Worn Out Tip: If your welding tip has been used excessively and is no longer sparking, it may be time to change your welding tip. This must be replaced as soon as possible as a worn tip can cause other welding problems.

Your MIG welder can fail for many reasons. To lengthen its life, make sure that it is always clean, frequently inspect its parts, and make sure that your power connection is constant, secure, and grounded.


Cracking is caused by a number of different things and is much less of a hassle to actively prevent than to fix. Cracking is usually caused because the stresses of the weld are too much for the seam or base material to handle. Stresses are caused by shrinkage as the weld cools.

Hot cracking occurs when the weld is at extremely high temperatures, usually above 1000 degrees. Hot cracks occur quickly and are usually caused by contamination. They can also be caused by spreading your beading too thin, making for a thin and brittle joint in your weld.

Cold cracking does not occur immediately, so it is not as easy to identify. It can occur days or weeks after you have finished welding. Cold cracking occurs because of hydrogen diffusion, where hydrogen collects around imperfections and contaminations in the weld. Make sure you are choosing the right filler and base to prevent this.

If you need to fix a crack, it is best to bore out the weld and redo it. Make sure that your freshly separated materials are clean and rust-free so that this does not happen again. If your base material is thin, you may want to preheat the material to make it more malleable and ready for the weld.


Erratic Arc

If your arc is crackling or flaring, it is likely because of a conductivity or wire-feeding problem. This can be fixed by taking apart your drive wire feeder for examination, cleaning, and repair.

First, make sure there is no dust or debris on your drive feeder. Then, make sure that your drive roll tension is adequate. Sometimes, it can be set too tightly, causing it to deform and fall into your weld. It could also be set too loosely, causing your wire to slip out of place.

Check inside of your liner. It should not be filled with debris. If it is, change it. Next, check your tip. Make sure that it is the right size for the job. If your tip is too big or too small it may be causing you issues. Also, be sure to regularly change your welding tips, as old tips can affect the quality of your welding and cause conductivity issues.

To actively prevent an erratic arc, be sure to:

  • Use good quality wires of the correct size
  • Clean out and replace liners when needed
  • Keep your machinery clean and examine regularly for wear and tear

Burnback on Contact Tips

Burnback occurs when your gun arcs and then burns back into the contact tip. This is usually caused by incorrect tip size or incorrect wire size. If your tip is too much bigger than your wire, then burnback is likely to occur. Make sure that your wire and tip are the same sizes to prevent this. 

Using a poor quality tip or wire material can also cause burnback. Make sure that you have chosen good quality, clean tools before you start, to prevent micro-arcing and poor conductivity. This will save you a lot of time and money in the long run. 

Worn/damaged liners and dirty base materials can also cause burnback. If this article has driven any one idea into the ground, it is that you need to have clean materials and workspace.


The Secret to Stopping Porosity | Welding Supplies From IOC (weldingsuppliesfromioc.com)

Are You a Mig Welder Whose Gun Wont Feed Wire? Here’s What to Check | ATTC (americantorchtip.com)

How to Prevent Lack of Fusion in Welding | Blackstone Advanced Technologies (blog.blackadvtech.com)

Weld Defects/imperfections in Welds – Lack of Sidewall and Inter-run Fusion | twi-global.com

5 Tips to Reduce Excessive Mig Welding Spatter | ATTC (americantorchtip.com)

Solving Spatter | weldingproductivity.com

Weld Distortion | The Lincoln Electric Company (lincolnelectric.com)

What Is Undercutting In Welding? | Gizmo Plans (gizmoplans.com)

Undercutting In Welding | weldsmartly.com

Preventing and Correcting Cracking | Welding Supplies From IOC (weldingsuppliesfromioc.com)

3 Problems with Contact Tips and How to Solve Them | Abicor Binzel (blog.binzel-abicor.com)

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