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Taming MIG Troubles: Tips for Solving Common Weld Defects

Tricks of the Trade: Seasoned welders will find some good troubleshooting tips in this back to basics primer from Tim Hensley of Hobart Brothers, while new welders can educate themselves toward building a solid foundation to advance their skills.

Posted: April 25, 2012


Tricks of the Trade: Seasoned welders will find some good troubleshooting tips in this back to basics primer, while new welders can educate themselves toward building a solid foundation to advance their skills.

With so many advancements in welding technology that are introducing new products, sometimes it’s easy to forget about the basics. Consider for a moment MIG welding, one of the most common welding processes but, like any process, one that takes time to master. Knowing how to quickly identify and solve some of the most common MIG weld defects when they occur is important – no matter your skill level. So even if you are a seasoned welding operator, it never hurts to revisit some good troubleshooting basics. Or if you are new to welding, taking the time to educate yourself can go far in helping you build a solid foundation to advance your skills.

First, porosity occurs when a gas pocket becomes trapped in the weld. Possible causes of this problem include, but are not limited to, an inadequate shielding gas coverage; a nozzle that is too small; and travel speeds that are too fast.

To solve this problem, first check gas flow rate, inspect hoses and fittings for leaks and increase shielding gas flow as necessary. Also be certain that the nozzle is free of spatter and that you are using one that is large enough for the application. Finally, slow your travel speed and hold the MIG gun near the bead at the end of the weld until the molten metal solidifies. Doing so prevents the gas coverage from being interrupted and leaving the setting weld exposed to the atmosphere. Using the correct shielding gas and properly cleaning base materials prior to welding can also help prevent porosity.

Another common weld defect, undercutting, results when a groove melts into the base metal next to the toe of the weld and the weld metal fails to fill that area. This can weaken the weld and may lead to cracking. To solve undercutting, reduce your welding current, decrease the welding arc voltage and adjust your MIG gun angle toward the joint. Reducing your travel speed can also help, as can pausing at each side of the weld bead if you are using a weaving technique.

Spatter, which occurs when the weld puddle expels molten metal and scatters it along the weld bead, is another common weld defect. Setting your wire feed speed and/or voltage too high can cause spatter. Too long of wire extension can cause also this. Try lowering the voltage and wire feed speed to solve the issue and reduce your wire extension. Also, be sure to use sufficient shielding gas and keep base materials clean to prevent spatter. Minimizing drafts, using the correct size contact tip and replacing worn contact tips can also help prevent this problem.

Excessive penetration and insufficient penetration are two additional weld defects that commonly occur. Excessive penetration results when the weld metal melts through the base metal and hangs underneath the weld. This is usually the result of too high of heat input and is best corrected by selecting a lower voltage range, reducing the wire feed speed and increasing your travel speed.

On the other hand, insufficient penetration occurs when there is not enough heat or the weld joint is designed poorly. Selecting higher wire feed speed, a higher voltage range and/or reducing travel speed are good ways to solve this problem. Proper joint preparation also helps prevent the problem by allowing sufficient access to the joint and providing a transition between the materials being welded that can be easily penetrated by the process.

Finally, incomplete fusion is another weld defect that can cause downtime and hinder productivity. This happens when the weld metal fails to fuse completely with the base metal or with the preceding weld bead in multi-pass applications. Holding the arc too far back in the weld pool and/or using an incorrect MIG gun angle most often causes this problem.

Remember to keep the arc on the leading edge of the weld puddle and maintain the travel angle between zero to 15 degrees. If using a weave technique, momentarily hold the arc on the groove sidewall. Maintain a steady travel speed and be certain that you are using the correct voltage and wire feed speed for your application.

Knowing these basics – whether you are a skilled welding operator or are new to the trade – can be a key in reducing costly downtime and increasing your productivity. Not to mention that some good troubleshooting skills can go a long way in helping you make high quality welds and reducing your frustrations.

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