MIG welding is a popular and versatile method of joining metals, but it can also produce some common defects that affect the appearance and strength of the weld. In this article, we will look at some of the most common MIG weld defects, their causes, and how to troubleshoot them.
I. Porosity
Porosity is the presence of small holes or bubbles in the weld metal, caused by gas trapped in the molten pool. Porosity can weaken the weld and make it more prone to cracking. Some of the possible causes of porosity are:
Poor shielding gas coverage: The shielding gas protects the weld pool from atmospheric contamination and oxidation. If the gas flow is too low, too high, or interrupted by leaks or drafts, it can cause porosity. To prevent this, check the gas regulator, hoses, and nozzle for proper flow and condition, and shield the welding area from wind or fans.
Dirty base material or filler wire: Any dirt, oil, rust, paint, or moisture on the base material or filler wire can introduce contaminants into the weld pool and cause porosity. To prevent this, clean the base material and filler wire thoroughly with a wire brush or solvent before welding.
Excessive wire stickout: The wire stickout is the distance between the contact tip and the arc. If the wire stickout is too long, it can cause excessive heating of the wire and gasification of the metal, resulting in porosity. To prevent this, keep the wire stickout between 1/4 inch and 1/2 inch for most applications.
For more about welding porosity, read Welding Porosity: Causes, Types, Effects, and Solutions.
II. Lack of Fusion
Lack of fusion is the failure of the weld metal to fuse completely with the base metal or the previous weld bead. Lack of fusion can create weak spots in the weld and reduce its load-bearing capacity. Some of the possible causes of the lack of fusion are:
Insufficient heat input: If the heat input is too low, the weld pool may not be hot enough to melt and fuse with the base metal or the previous weld bead. To prevent this, increase the voltage or wire feed speed to raise the heat input and create a larger weld pool.
Improper travel speed or gun angle: If the travel speed is too fast, the weld pool may not have enough time to fuse with the base metal or the previous weld bead. If the gun angle is too steep or too shallow, it may cause uneven heat distribution and fusion. To prevent this, maintain a consistent travel speed that matches the heat input and keep a 0- to 15-degree gun angle relative to the workpiece.
Magnetic arc blow: Magnetic arc blow is a phenomenon where the arc is deflected by magnetic fields around the workpiece, causing erratic arc movement and poor fusion. Magnetic arc blow can be caused by residual magnetism in the workpiece or by improper placement of the ground clamp. To prevent this, demagnetize the workpiece before welding and place the ground clamp as close as possible to the weld area.
III. Burn-through
Burn-through is when the weld metal penetrates completely through the base metal, creating a hole in the workpiece. Burn-through can compromise the integrity of the weld and cause distortion or warping of thin materials. Some of the possible causes of burn-through are:
Excessive heat input: If the heat input is too high, it can melt through thin materials quickly and create burn-through. To prevent this, reduce the voltage or wire feed speed to lower the heat input and create a smaller weld pool.
Slow travel speed: If the travel speed is too slow, it can cause excessive heat buildup and burn-through. To prevent this, increase the travel speed to move the weld pool faster along the joint.
Improper joint design: If the joint design is not suitable for MIG welding, it can cause burn-through. For example, a butt joint with no gap or root opening can trap heat and cause burn-through. To prevent this, use an appropriate joint design for MIG welding, such as a V-groove, U-groove, or J-groove, and leave a small gap or root opening for heat dissipation.
IV. Conclusion
These are some of the most common MIG weld defects, their causes, and how to troubleshoot them. By following these tips, you can improve your MIG welding skills and produce high-quality welds. However, remember that MIG welding requires practice and experience, and that some defects may require professional repair or rework. Always follow safety precautions and wear proper protective equipment when welding. You can also read Welding Defects, Problems, And Easy Solutions [2023] to grasp more tips for handling welding defects and problems.
