One of the most labor-intense operations in the fabrication of sheet metal duct is welding.

Processes used

Wire or MIG (Metal Inert Gas) (SMAW – Shielded Metal Arc Welding)
Wider weld as compared to TIG
Some weld splatter
Structurally as sound as TIG
Faster welding compared to TIG
Less welding cost compared to TIG
The weld appearance is not as neet as a TIG weld.

Heliarc or TIG (Tungsten Inert Gas) (GTAW – Gas Tungsten Arc Welding)
Very neat weld
Applicable usually to stainless and aluminum
Used for exposed duct installations where the weld will be visible
Used only where high quality weld is a must
Six times the weld cost of MIG

Cleaning of Welds
TIG and MIG welding of stainless steel leaves a narrow band of discoloration along the weld line approximately 1/8” wide. To remove this discoloration an additional process is required after welding. This process will remove approximately 90% of the discoloration.

Grinding of Welds
Performed on butt welds - This is to remove excessive internal welding slag
protrusions, which will generally provide a snag free internal surface. There is no
grinding on the external surface of wire welds.

Lapped and fully wire welded
This is the standard production procedure for L & L on a fully welded assembly.
The seam is offset rolled, lapped over the other edge and welded on the outside
seam. This method does not require any internal grinding.

Polish the weld
The appearance of stainless steel # 3 & #4 is a brushed finish. This material can
have the Heliarc weld brushed in the direction of the surface to help “hide” the
weld. This will not completely ‘hide’ the weld.