Cracking, spatter, incomplete fusion: just a few of the many pitfalls you may face when attempting a weld. While no approach is completely foolproof, your chances of a successful weld are much better once you have a good understanding of the basics. It is also important to tailor your methods to your choice of material; what works best for one type of stainless steel may not be as helpful with another. In this case, we’ll examine a few of the most popular methods of stainless steel welding.
The Material
There are many different grades of stainless steel, but they all have at least one alloying element in common: chromium. The addition of chromium is what makes steel ‘stainless’, with its characteristic shine and boosted corrosion resistance. However, adding chromium to the steel’s chemical composition – along with other elements such as molybdenum, silicon, or manganese – affect how the metal will react to heat. These elements lower the thermal conductivity of stainless steel, which means heat will not spread as easily through the material. This lack of efficient conductivity requires a stronger heat input, but higher temperatures or an extended welding time increases the chances of a burn-through or other heat-related faults. Whatever process you use for welding stainless steel, it will be a matter of balancing necessary heat input vs the potential for heat damage.
The Processes
There are several different methods of welding stainless steel, but most welders use one of these three types. There are other factors that can be considered in more detailed, but generally the selection depends upon the material’s thickness:
1. Tungsten Inert Gas (TIG) welding
This process is one of the most commonly used for welding stainless steel. TIG welding, often referred to as tungsten gas arc welding, creates a low heat input which makes it the best choice for thinner materials. The heat is generated using electricity, which powers an electric arc between the tungsten electrode and the base metal. An inert gas such as argon creates a sheathing environment around the electrode, protecting and cooling the tungsten. This dampening effect helps to keep a relatively low heat input, as well as creating less smoke and oxidation.
Low heat input means TIG welding is ideal for thin stainless steels or precision welds on critical joints. Its concentrated heat allows for a narrow fusion zone, which calls for a high degree of control over the welding process. After completion, a TIG-produced join requires little to no post-weld finishing.
2. Metal Inert Gas (MIG) welding
Also known as gas metal arc welding, MIG uses electricity to melt and join metal during a weld. However, unlike TIG welding, MIG requires the use of both an inert shielding gas and a solid wire electrode. This filler metal wire is continuously fed during the welding to create the arc between the electrode and base metal.
Due to the higher heat during the weld, MIG is best selected when welding thicker widths of stainless steel or steel plate. It can be adapted for semi-automatic welding processes, since the continuous wire feed allows for long joins. It also produces little spatter and easy cleanup after processing.
3. Resistance welding (RW)
TIG relies upon a welding operator and MIG can be done manually or through automation, but for manufacturers who require a highly automated process, resistance welding is key. The method involves an electrical current run through weld electrodes, which apply force to the pieces being joined (the “resistance” part of the process). This force is converted to heat, and the resulting heat melts the metal enough to join it together. When completed successfully, the molten metal at the point of contact will form a rounded weld, known as a “nugget”.
Unlike the other two processes, RW has a steep initial cost of equipment setup and requires a high amount of power. This means it has little portability and cannot be used in the field like TIG and MIG welding. However, for manufacturing purposes, resistance welding is ideal. It is fast, reliable, requires no filler metals or other materials, and is excellent for sheet metal applications. Stainless steel can get up to weld temperature very quickly using the RW method, so welding can be completed within a few milliseconds.