TIG welding (GTAW)
TIG welding is widely used in the fabrication sector for stainless steel since it has a stable arc and the process is automated. In the TIG process, the heat applied to the weld can precisely be controlled through a foot pedal or finger control, minimising the possibility of warping. TIG welding machines can also switch between AC and DC polarities, offering flexibility and convenience simultaneously.
MIG welding (GMAW)
MIG welding is another popular choice for welding stainless steel. It offers faster speeds than TIG welding mainly thanks to its continuously fed electrode. One downside of this technique is that it doesn’t look as pleasing to the eye as properly executed TIG welds.
A Teflon wire liner in the MIG gun allows for a consistent wire feed to the weld pool and added protection from contamination. Backstepping, staggering or allowing the joint to undergo a bit of the cooling process helps avoid warpage since stainless steel retains heat well.
Shielded metal arc welding (SMAW)
Stick-welding stainless steel is often the practical choice regarding cost, portability and simplicity. SMAW can be performed in almost any environment and thus is great for various repair jobs and welding stainless steel outdoors.
Thicker pieces of stainless steel (above 2mm) are most suitable for SMAW since it is harder to control the heat input than with other methods. Selecting the electrode (typical grades: 316, 308, or 312) is an important part of the project. Beware of slag removal after the welding as it might be a bit of a struggle.
Flux cored arc welding (FCAW)
Flux-cored arc welding stainless steel is sometimes preferred over SMAW since it generally creates a more uniform weld bead. FCAW can be performed with a shielding gas when working with varying material thicknesses or in demanding welding conditions.
A 10° drag angle allows the flux to rise at the weld pool and gives enough bead coverage.
Resistance welding
Resistance welding (spot welding, seam welding) stainless steel creates clean welds compared to arc welding processes since it doesn’t use filler material and has no risk of weld spatter. The high electrical resistance of stainless steel is also favorable since it can complete a weld in a short amount of time.
A good quality welder with sufficient power output is necessary for resistance welding stainless steel to prevent the areas close to the HAZ from deformities. It is recommended to have higher current and voltage values when welding stainless steels compared to, for example, copper and aluminium alloys due to the difference in electrical conductivity.
Friction welding
Friction welding stainless steel, similar to resistance welding, doesn’t use consumables, making it an economical choice when the part geometries allow for it. It is most suitable for welding austenitic stainless steel due to its composition of chromium (16-26%) and nickel (8-22%).
Some factors that need to be considered are friction pressure, burn-off length and rotational speed. Some sub-types of friction welding may be suitable for specific applications: friction hydro pillar processing (FHPP), friction stir welding (FSW) and friction plunge welding.