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WeldTips #4: Troubleshooting MIG Welding Defects and How a Robot Can Help

Updated: May 6

Enhancing MIG Welding Quality: How Robotics Can Minimize Defects


MIG (Metal Inert Gas) welding is a staple in various industries because of its versatility and efficiency. However, like any welding technique, MIG welding is susceptible to defects and discontinuities that can undermine the integrity of welded joints. This article clarifies the difference between a “discontinuity” and a “defect” and describes how robots can help minimize these issues in MIG welding.


Distinguishing Discontinuity from Defect

It’s vital to differentiate between “discontinuity” and “defect” in the realm of welding:


  • Discontinuity: An interruption or irregularity in the weld that may not necessarily impair the structural integrity. Common types include porosity, cracks, undercutting, and lack of fusion. Certain discontinuities are acceptable under various welding codes and standards, so long as they don’t degrade the weld’s mechanical properties or functionality.


  • Defect: A more severe form of discontinuity that directly compromises the weld’s structural integrity, rendering it unfit for its intended purpose. Defects typically arise from extreme discontinuities or their combinations, requiring immediate rectification to avert potential failures.


Common MIG Welding Defects and Solutions

1. Porosity

Cause: Arises primarily from inadequate shielding gas coverage, leading to atmospheric gas entrapment in the weld pool. Gasses in the atmosphere are not conducive to sound welds and get trapped in the molten weld pool. As the puddle cools, those gasses try to escape, creating holes in the weld. Dirty base materials can also contribute to porosity.


Solution: To effectively tackle porosity in MIG welding, be sure to maintain ideal contact tip-to-work distance and gun angles while diligently cleaning and preparing the welding surface. Optimizing shielding gas flow rates is also crucial. Increasing the gas flow rate when encountering porosity is a common mistake, but typically, a flow rate between 25 and 40 CFH is adequate. Exceeding this can lead to gas wastage and, paradoxically, cause more porosity by introducing atmospheric gasses into the shielding gas through turbulence.


For welding steel, eliminating porosity is usually straightforward. With aluminum, the challenge intensifies beneath the surface of the weld. However, since subsurface porosity rarely undermines the weld’s structural integrity, a completely porosity-free aluminum weld is seldom required. The principles applicable to steel for surface porosity also hold true for aluminum.


2. Cracks

Cause: Result from excessive welding stress, improper cooling rates, or flawed joint designs.

Solution: Adjust welding parameters, apply pre-weld or post-weld heat treatments, and enhance joint design and preparation. Restraints on materials should be minimized to avoid cracking, which is rare in mild steel and generally manageable.


3. Undercutting:

Cause: Caused by excessive voltage or an improper electrode angle, undercutting can result in a groove along the weld’s edges, leading to weakened joints.


Solution: Maintain proper torch angles and voltage settings. More voltage widens the arc cone, causing the metal to melt away. However, this will leave an unsatisfactory transition from the weld metal to the base metal if insufficient weld metal is not filled in.


4. Spatter:

Cause: Excessive spatter occurs when tiny molten metal droplets are expelled from the welding puddle, leading to rough, uneven weld surfaces.


Solution: Dial in the correct welding parameters and avoid using poor-quality consumables. Spatter is typically due to insufficient voltage. The wire harshly comes in contact with the weld puddle, splashing molten metal around the weld and creating spatter. Some metal transfer modes, such as CV Spray, should result in almost zero spatter, whereas a short-circuit transfer is expected to have some spatter, but it should be easily removable.


Robotic Precision in MIG Welding

Robots can replicate exact movements down to the thousandth of an inch, eliminating defects when proper weld settings and torch angles are used. Considering the costs associated with correcting poor welds, the accuracy and efficiency of robots offer a quick return on investment. Plus, you don’t need to be technology-savvy to program a welding robot. Advances in robotic welding technology have made parameter settings more user-friendly, enabling operators to learn effective robotic welding techniques quickly.


MIG welding defects and discontinuities jeopardize the quality and safety of welded joints. However, integrating robotic welders into the MIG welding processes offers a promising solution. Robots bring unmatched consistency and precision, significantly reducing defects and elevating the overall quality of welding operations.

From the Productive Robotics Weld Team

This article was written by our Weld Team. Productive Robotics is the leading American manufacturer of collaborative robots for welding, CNC machine tending, and more. All of our welding robots feature the following;


·         Zero programming. No robot experience needed

·         Teach a weld faster than it takes to weld by hand

·         Repeat the same weld perfectly every time.

·         7 Axis robot: More maneuverability for less fixturing

·         Online Support by experienced, degreed welders


Have a question or need more information? Talk with a welding and robotics expert: 805.244.9300 or download this guide to the world's largest range of welding cobots.

Download welding cobots guide


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