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For this article we are just going to focus on the standard processes that are used most in fabrication today and these will be:

• SMAW, Shielded Metal Arc Welding

• FCAW, Flux Cored Arc Welding

• MCAW-SP, Metal Cored Arc Welding in Spray

• GTAW, Gas Tungsten Arc Welding聽聽

• GMAW-SP, Gas Metal Arc Welding in Spray聽

• SAW, Submerged Arc Welding

We will discuss each process, their deposition efficiencies and deposition rates in order to understand the advantages and disadvantages of each in productivity.

The definition of Deposition Efficiency is the amount of the electrode that becomes weld metal and Deposition Rate is the amount of weld metal deposited in a given time, i.e.,聽 Kg鈥檚 per hour of deposited metal.聽

Shielded Metal Arc Welding (SMAW)

The deposition efficiency of SMAW is 60-65% which means that only two thirds of the electrode becomes weld metal and the other 30% is made up by stub loss and the slag deposit. The deposition rate of SMAW depends on the size of electrode, amperage, and position of welding. For example, a 3.2mm E4918 electrode at 140 amps, welded in the flat or horizontal position, deposits 1.2 kgs/hour.聽 The other factors are that SMAW is a manual process which uses a coated electrode in lengths of 300mm (12鈥�), 355mm (14鈥�) and 457mm (18鈥�), so the maximum electrode deposited is the length of the electrode less almost 30% of stub loss. Each electrode must be manually changed, the slag deposited manually removed and the weld cleaned after each electrode completion. This makes this process not effective in production, but it works well in the field and for out of position welding on steel from 3mm and above.

Flux Cored Arc Welding (FCAW)

This process is much higher than SMAW in efficiency at 82-85%. The deposition rate also depends on size of wire electrode, amperage, and position of welding. For example, a 1.4mm (0.052鈥�) E491T-9M-H4 wire electrode at 250 amps, welded in the flat or horizontal has a deposition rate of 3kgs/hour. The advantage over SMAW is that this process is classed as semi-automatic, which means the electrode comes on a spool containing approximately 20KG of flux cored wire so there are less time wasted changing electrodes and more continuous welding or arc on time. The higher efficiency means that up to three quarters of the electrode becomes weld metal and the only loss is through slag deposits. Also, because of the semi-automatic nature of the process more weld metal can be deposited per spool of wire as compared with SMAW.聽

The slag deposit must be removed manually, and the weld cleaned after every deposit and the amount of welding is dependent on the reach of the individual person welding. However, this process can be automated and larger spools or packaging of wire electrode can be used. This also increases the deposition rate and make this process more productive on steel for materials 5mm and above in all positions.

Metal Cored Arc Welding (MCAW)

This process is one of the highest in deposition efficiency at 94-98% which means almost all the wire electrode is deposited as weld metal. The deposition rate again depends on the size of wire electrode, amperage, and position of welding. For example, a 1.4mm (0.052鈥�) wire electrode at 250 amps welded in the flat or horizontal positions has a deposition rate of 3.5 kgs/hour. This process forms no slag and, therefore,聽 with non to be removed more time is spent in depositing metal. Also, this process can be automated again using larger packaging of wire electrodes making this process even more productive over SMAW and FCAW on steel from 3mm and above, in the flat and horizontal positions only.

Gas Metal Arc Welding (GMAW)

This process is also one of the highest in deposition efficiency at 92-99% which means almost all the wire electrode becomes weld metal. The deposition rate of GMAW again is dependent on the size of the wire electrode, amperage, and position of welding. For example, using a 1.2mm (0.045鈥�) diameter wire electrode at 250 amps and welding in the flat or horizontal position the deposition rate is 4.54 kgs/hour. This process can also be automated and using larger packages of wire electrodes this would be very productive on steel from 3mm and up using the correct wire electrode diameters.

Gas Tungsten Arc Welding (GTAW)

Although this process has a high level of deposition efficiency 94-99%, GTAW is a manual process. The electrode is deposited manually and comes in a certain length of 1M and must be manually changed. The deposition rate for GTAW is as low as SMAW with an average 0.9-1.4 kgs/hour. The process can be performed in all position, and this will further reduce the deposition rate.聽

Although most of the electrode becomes weld metal, being a manual process, the deposit of metal is much slower that the semi-automatic processes. However, this process can be increased for higher productivity by automation using either cold or hot wire feedings systems to increase deposition rates to that of GMAW.

Submerged Arc Welding (SAW)

This process looks to be the best in deposition efficiency at 99%, which means almost all the wire electrode becomes weld metal. The deposition rate is also much higher than the other processes and this due to the larger diameter wire electrodes that can be used. As an example, using a 4mm (5/32鈥�) diameter electrode and welding at 900 amps in the flat position the deposition rate is 12 kgs/hour. However, this process requires a covering of flux, hence the word submerged. The welding is performed under the flux cover which creates a slag deposit that must be removed each time one completes the weld. The SAW process is automated and it can weld continuously on its own with a welding operator controlling the process and it is performed in the flat and horizontal positions. It is predominantly used on thicker materials because of the high deposition rates.

Looking at the list above we can estimate that the GMAW and MCAW processes are the most productive on structural steel fabrications and SAW would be the most productive when welding thicker materials such as wind energy towers, pressure vessels, marine and offshore structures,聽 just to name a few.聽

Also, we see that determining what process is the most productive is not as simple as looking at deposition efficiencies or deposition rates. One should contact their local welding suppliers or welding specialist to assist in determining the most productive process for their specific applications .