How to Make MIG Weld Fillet Concave: A Comprehensive Guide

Creating a concave MIG weld fillet can be a challenging task, but with the right techniques and understanding of the welding parameters, it can be achieved. This comprehensive guide will provide you with the necessary information and expert-level details to help you master the art of making a concave MIG weld fillet.

Adjusting Welding Parameters

The key to achieving a concave weld profile lies in the proper adjustment of the welding parameters, including travel speed, voltage, and wire feed speed.

Increasing Voltage and Reducing Wire Feed Speed

One effective method to create a concave weld profile is by increasing the voltage and reducing the wire feed speed. This combination results in a hotter arc, which can melt more metal and produce a deeper weld profile. However, it is crucial to avoid overheating the metal, as this can lead to warping and distortion. To mitigate this, it is recommended to make multiple passes with a lower heat input, gradually building up the weld bead.

Optimizing Travel Speed

Another critical factor in achieving a concave weld profile is the travel speed. Decreasing the travel speed can result in a wider weld bead with the same concave profile. It is essential to find the right balance between travel speed and heat input to achieve the desired weld profile. Experiment with different travel speeds and monitor the results to determine the optimal setting for your specific application.

Adjusting Welding Gun Angle and Workpiece Position

The weld profile’s concavity or convexity can also be affected by the welding gun’s angle and the metal’s position. It is recommended to hold the welding gun at a 70 to 80-degree angle to the workpiece and maintain a consistent travel speed and distance from the workpiece. This positioning helps to ensure proper penetration and fusion, contributing to the desired concave weld profile.

Utilizing a More Powerful Welder

how to make mig weld fillet concaveImage source: Mig weld example

In addition to adjusting the welding parameters, using a more powerful welder can also help achieve a concave weld profile. A higher heat input from a more powerful welder can melt more metal, resulting in a deeper weld bead and a more pronounced concave profile. However, it is crucial to exercise caution and avoid overheating the metal, which can lead to distortion and other quality issues.

Monitoring Weld Quality

To ensure the weld quality and the desired concave profile, it is recommended to use a welding gauge to check the weld’s flatness and identify any defects. A flat weld edge indicates good penetration and fusion, while a concave or convex weld profile may indicate poor penetration or lack of fusion.

Avoiding Excessive Concavity

It is important to note that a completely concave weld is not desirable and can lead to poor weld quality. Instead, the weld profile should be mostly flat with a slight concavity. Excessive concavity can result in stress concentrations, reduced fatigue life, and other structural integrity issues. Therefore, it is crucial to strike a balance between achieving the desired concave profile and maintaining the overall weld quality.

Practical Tips and Techniques

  • Start with a clean and well-prepared base metal surface to ensure proper weld penetration and fusion.
  • Use a welding wire with the appropriate diameter and composition for your specific application.
  • Maintain a consistent travel speed and distance from the workpiece to ensure uniform heat input and weld profile.
  • Consider the use of a welding positioner or fixture to help maintain the desired gun angle and workpiece position.
  • Experiment with different welding parameters and techniques to find the optimal settings for your specific project.
  • Regularly inspect the weld and make adjustments as needed to maintain the desired concave profile.


Creating a concave MIG weld fillet requires a deep understanding of welding parameters and a keen eye for detail. By adjusting the voltage, wire feed speed, travel speed, and welding gun angle, you can achieve the desired concave profile while ensuring the overall weld quality. Remember to use a welding gauge to monitor the weld’s flatness and avoid excessive concavity, which can compromise the structural integrity of the joint. With the right techniques and attention to detail, you can master the art of making a concave MIG weld fillet.