How to MIG Weld Stainless Steel Like a Pro

Stainless steel is a versatile and durable metal that is widely used in various industries, such as construction, engineering, automotive, aerospace, and more. It has excellent corrosion resistance, strength, and aesthetic appeal. But how do you weld stainless steel? What are the best methods and techniques for joining this metal?

In this article, we will answer these questions and provide some tips and tricks for welding stainless steel successfully while focusing on one common welding process: MIG (metal inert gas) welding.

The Benefits of MIG Welding Stainless Steel Over Other Methods

MIG welding can be used to join stainless steel metals together rather than utilizing other welding methods, such as gas tungsten arc (GTAW) or oxyacetylene.

• Speed and Cost-Effectiveness: MIG welding allows for quicker completion of welding projects compared to alternative techniques, enhancing productivity and cost-effectiveness.
• Versatility: MIG welding can be used with both thick and thin materials, making it suitable for a wide range of applications.
• Corrosion Resistance: The molybdenum content in stainless steel ensures outstanding corrosion resistance, surpassing many other metals and alloys.
• Lower Contaminant Levels: MIG welding is conducted at a lower temperature and with relatively fewer contaminants in the air, making it a favorable option over other welding processes.

Tips for MIG Welding Stainless Steel

Stainless steel can be successfully welded using a MIG welder, but it is important to understand some of the basic technical considerations prior to beginning your welding project. Before beginning to weld, the surfaces of the join should be prepared to ensure proper coverage and adherence. The surface should be properly prepared before attempting to weld stainless steel, by scraping off any dirt or rust and cleaning the area with a wire brush. Additionally, it is essential to use the right size of MIG wire in order to achieve a strong weld; this can vary depending on the base metal thickness, position of welding, and amperage of the machine.

After preparations are complete, a balanced arc should be established between the workpiece and the electrode using a suitable shielding gas mixture. The shielding gas affects the arc stability, weld quality, penetration, and appearance of the weld.

The most common shielding gas for MIG welding stainless steel is a mixture of argon and carbon dioxide (CO2). The argon provides a smooth and stable arc, while the CO2 enhances the penetration. The ratio of argon to CO2 can vary depending on the type and thickness of the stainless steel, but a typical range is 75% to 85% argon and 25% to 15% CO2.

Some welders prefer to use a tri-mix gas, which consists of argon, CO2, and helium. The helium adds heat to the arc, which can improve the weld penetration and appearance. However, helium is more expensive and can cause more distortion than argon-CO2 mixtures.

You should avoid using pure argon or pure CO2 as shielding gases for MIG welding stainless steel. Pure argon will result in poor arc stability, low penetration, and inconsistent welds. Pure CO2 will cause excessive spatter, oxidation, and porosity.

The welding wire should match or be close to the composition of the base metal. This will ensure good weldability, strength, and corrosion resistance.

There are many grades of stainless steel welding wires available in the market. Some of the most common ones are:

• ER308L: Suitable for welding 18-8 austenitic stainless steels, such as 304 and 304L.
• ER309L: Designed for welding dissimilar metals, such as stainless steel to carbon steel or low alloy steel.
• ER316L: Ideal for welding 18-12 austenitic stainless steels with molybdenum content, such as 316 and 316L.
• ER308LSi: Similar to ER308L but with higher silicon content that improves the wetting action and fluidity of the weld pool.
• ER309LSi: Similar to ER309L but with higher silicon content that enhances the weldability and appearance of dissimilar metal welds.
• ER316LSi: Similar to ER316L but with higher silicon content that improves the weldability and appearance of molybdenum-containing stainless steels.

The diameter of the welding wire depends on the thickness of the base metal and the desired weld bead size. Generally speaking, thinner wires are better for thinner metals and smaller welds, while thicker wires are better for thicker metals and larger welds.

The typical wire diameters for MIG welding stainless steel range from 0.023 inches to 0.045 inches (0.6 mm to 1.2 mm).

The welding technique for MIG welding stainless steel is similar to that of MIG welding mild steel. However, there are some differences that you should be aware of.

One difference is that you should use a lower voltage and amperage setting than you would for mild steel. This is because stainless steel has higher electrical resistance and lower thermal conductivity than mild steel. If you use too high voltage or amperage, you will risk burning through the metal, causing distortion, or creating a brittle weld.

Another difference is that you should use a shorter stick-out length than you would for mild steel. The stick-out length is the distance between the contact tip and the end of the wire. A shorter stick-out length will provide better arc control and reduce the chances of wire stubbing or burnback.

A third difference is that you should use a push or forehand technique rather than a drag or backhand technique. The push technique means that you angle the torch slightly forward and move it away from the weld pool. The drag technique means that you angle the torch slightly backward and move it toward the weld pool.

The push technique is preferred for MIG welding stainless steel because it creates a flatter and smoother weld bead with less spatter and oxidation. The drag technique can cause more spatter and oxidation, as well as a narrower and deeper weld bead that may lack fusion.

To ensure precise welding, it's essential to direct the flame accurately to the desired area. Achieving this precision involves positioning the torch at a 30-degree angle from the joint end. For different welding scenarios, the ideal travel angle should be considered. A travel angle ranging from 5 to 15 degrees, while maintaining a 90-degree gun orientation, yields the best results.On the other hand, when dealing with T-joints and lap joints, opting for greater angles in the range of 45 to 70 degrees is recommended.

Examples of Projects With MIG Welding Stainless Steel

MIG welding stainless steel can open up a range of potential projects. It can be used to create custom brackets and structural components for various industries, such as construction, engineering, automotive, aerospace, and more. You can also take advantage of its superior corrosion resistance to join many types of duplex and ferritic alloys that are used in harsh environments.

Additionally, it can be used for commercial fabrications that require excellent weldability but can also provide aesthetic appeal when tackling decorative pieces like home and garden art. What truly makes MIG welding stainless steel invaluable is that it can handle a variety of alloys without needing to switch processes or materials, making complex projects easier and faster to complete while lowering overall costs.

In conclusion, MIG welding stainless steel is a feasible and effective process that can produce high-quality welds with high speed and efficiency. However, it also requires some special considerations and adjustments when compared to welding mild steel. By choosing the right shielding gas, welding wire, and welding technique, you can achieve optimal results and avoid common problems.

If you have questions about MIG welding stainless steel or are looking for help with a project, don’t hesitate to contact us. We’re more than happy to provide advice or resources as needed. In the meantime, check out our website for engineering tools and parts that can make your next project a success.