Welding is a basic skill that can be useful in a number of situations. Read on to know more about the different types and techniques of welding...
A Quick Comparison Between SMAW, FCAW, and GMAW Welding Methods
The main difference between the SMAW, FCAW, and GMAW welding methods is in the material used to protect the weld pool from atmospheric contamination. But there’s much more than just this. ScienceStruck gives you the comparison between these methods in more detail.
Did You Know?
Welding was first used as far back as 3,500 BC, during the Bronze Age. Drawings of welders and their tools have even been discovered in the Egyptian pyramids.
Welding is a method used to bind pieces of metal together by heating them to their melting points, and adding a molten material called a filler material at their joints. These molten metals form a weld pool at the joint, which then cools and solidifies, joining both pieces together. The technique used to heat the base metal can vary, depending on the method and its application. But the most common methods involve the use of electricity or a gas torch.
Electricity is often used in welding to create an electric arc between an electrode and the base metal, causing high temperatures which are enough to melt both. Commonly, the filler material used to join the metal pieces is itself used as the electrode. However, once the weld pool is formed, the hot metal can be easily weakened by oxidation.
To prevent contamination, the weld pool needs to be insulated from the atmosphere. This is usually done by using materials called flux, which melt along with the electrode to form a protective coating called slag, on the weld pool. Another method is to eject an inert gas on the weld pool from a nozzle, so that it drives away the air around the molten metal, thereby insulating it. Such a method of welding is called electric arc welding. Common examples of this method are Shielded Metal Arc Welding, Flux-cored Arc Welding, and Gas Metal Arc Welding. The important difference between the SMAW, FCAW and GMAW welding methods are listed here.
Comparison SMAW vs. FCAW vs. GMAW
Shielded metal arc welding is a method that makes use of stick electrodes, in which the electrode surface is coated with a layer of flux. As the electrode melts, the flux gives off a shielding gas, and also melts to form slag, both of which cover the surface of the weld pool.
Flux-cored arc welding is a process that uses a tubular electrode, in which the outer shell is made of the electrode metal, while the inner hollow is filled with flux. This flux melts to form a protective coating of slag around the weld pool, and also gives off a shielding gas.
Gas metal arc welding is a method in which a wire electrode is used for welding, and a flux is not added. A shielding gas is ejected directly from the welding gun, which covers the surface of the weld pool that is formed.
► An electrode is placed in the holder, and the electric supply (either direct or alternating) is turned on.
► The electrode is lightly tapped on the metal work piece and immediately withdrawn. This sets up an electric arc.
► The high temperature of the arc melts both, the electrode and the work piece. Beads of metal are transferred from the electrode onto the work piece, to form a weld pool.
► The flux on the electrode melts and forms slag, which is transferred to the weld pool. Being lighter, it floats and covers the weld pool.
► A shielding gas is given off by the melting of flux. This also covers the weld pool and prevents any contamination from the atmosphere.
► The process has to be stopped periodically to replace the electrode. When the weld pool solidifies, the slag layer is chipped off.
► First, a constant-voltage electric supply is set up.
► On pressing the trigger, the wire feeder begins ‘feeding’ the electrode to the joint. This electrode does not need to be replaced periodically, like in SMAW.
► As in SMAW, the electrode, on being tapped and withdrawn, sets up a high temperature electric arc.
► The electrode begins melting and transfers its metal to the welded joint in the form of a puddle.
► Simultaneously, its flux core also melts to form slag, which floats on the weld pool. It gives off a shielding gas, which protects the welded metal from oxidation.
► If required, a dual-shield FCAW may be carried out, in which additional shielding gas is ejected manually from an external supply.
► Like in SMAW, the slag has to be chipped off on cooling.
► After selecting the required shielding gas pressure and rate of wire feed, the DC supply is turned on. An AC supply is never used for GMAW.
► Like SMAW and FCAW, the electric arc is set up by tapping and withdrawing the electrode wire.
► As the metal is transferred from the electrode to the weld pool, the shielding gas is simultaneously ejected on the metal by a diffuse or nozzle on the welding gun.
► Unlike SMAW, changing an electrode after it is used up is unnecessary, as a wire feeder continuously supplies the gun with the electrode wire.
◆ It is used to weld ferrous metals like carbon steel, alloy steel, stainless steel, cast iron, and ductile iron.
◆ Though rare, its non-ferrous uses include welding nickel, copper, titanium, and aluminum, along with their alloys.
◆ It is generally used in fabrication work, including structural steelworks and shipbuilding tasks.
◆ It is used in tasks like repair and maintenance.
◆ It is commonly used in tube and pipe applications.
◆ It is used in construction and maintenance of several industries, including shipbuilding, oil refineries, chemical plants, gas industries, petroleum, mining, road-building, cement, pulp and paper industries, and power plants.
◆ It is used in the manufacture of parts like machine screws, valves and valve seats of internal combustion engines, nuclear plant parts, agricultural equipment, and cutting tools.
◆ It is used on ferrous alloys like steel, and some non-ferrous alloys like those of nickel.
◆ It can be used for alloys and metals like stainless steel, mild steel, and aluminum.
◆ It is used by the automotive industry, sheet metal industry, construction, and shipbuilding industry.
◆ It is used for robotic welding, general repair workshops, ship repair yards, and office furniture assembly.
◆ It is widely used in any task involving pipework, fabrication, and brazing work.
▲ SMAW has the lowest cost when compared to both, GMAW and FCAW, since it does not require a gas cylinder, hose, flow meter, or wire feeder.
▲ Both, the equipment and electrodes are highly affordable. Plus, the method is very simple.
▲ The equipment is highly portable, since the only thing required is a generator.
▲ The stick electrodes take up very little space and are also bendable, so welding can be done in confined spaces and in various positions.
▲ Welding can be carried out both, indoors and outdoors, even in moderate wind, since an external supply of shielding gas is not required.
▲ The method is highly versatile, can be used for a variety of applications, and can also use a wide range of electrodes.
▲ It uses a continuously-fed wire electrode, which does not require periodic replacement like the stick electrodes of SMAW.
▲ The metal surface does not need pre-cleaning.
▲ It has a high deposition rate and efficiency when compared with SMAW. It has a better deposition rate as compared to GMAW when used on non-flat surfaces.
▲ Some methods do not require any external shielding gas supply, and can be used both, indoors and outdoors, even in mild windy conditions.
▲ This method of welding can be performed in a variety of positions.
▲ It is simpler to perform than SMAW, and requires a less-skilled operator.
▲ A single electrode size can be used on a range of metals with different thicknesses.
▲ It can be used in certain high-speed operations, such as those in the automotive industries.
▲ This process can be automated, especially parameters like shielding gas delivery rate and wire feed.
▲ When compared to SMAW and FCAW, this process does not form any slag, leading to reduction in labor costs.
▲ This method uses a wire feeder, which does not require periodic electrode replacement like the stick electrodes of SMAW.
▲ The method has lower weld spatter levels when compared to the other two.
▲ The method does not require a highly-skilled operator.
▲ It has a high deposition efficiency and better weld quality, since there is no risk of slag entrapment.
▲ Metal wastage is reduced, as there are no electrode stubs like that in SMAW.
▲ This method is faster and can be applied to a variety of metals and alloys.
▼ Stick electrodes have to be replaced when used up. On an average, only 25% of the operator’s time is spent actually welding, which reduces productivity.
▼ The slag has to be manually chipped off when the weld pool cools, or else, it may weaken the metal.
▼ This process has a low rate of deposition when compared to the other two.
▼ The operator needs to be skilled with good hand-eye coordination.
▼ The electrode butts (ends) have to be disposed, causing metal wastage.
▼ It has quality issues, such as porosity, cracking, weld spatter, and shallow penetration.
▼ Depositing a certain, specific quantity of material can be costlier.
▼ This process releases toxic smoke, which can be harmful.
▼ It is not recommended for metals thinner than 20 gauge.
▼ The smoke generated in this process is the most toxic, as compared to the other two.
▼ When the electrode gets used up, the entire spool has to be replaced, which takes longer than the other two methods.
▼ When compared to GMAW, the electrode and equipment is costlier.
▼ This welding method requires stringent parameters, or else the welded joint lacks toughness, or suffers from lack of fusion.
▼ The equipment is bulky and less mobile, which does not allow welding in tight spaces.
▼ The slag formed is tougher to remove.
▼ The position in which the gun is held is critical for good performance.
▼ The compulsory requirement of shielding gas is a drawback.
▼ It cannot be used outdoors, as winds can displace the shielding gas from the weld pool.
▼ Depending on the type of gas used, the initial setup can be costlier.
▼ It has higher maintenance costs due to more electronic equipment used.
▼ The wire feeder used can have certain maintenance issues, and reduces mobility.
▼ Overhead and vertical welding is not possible because of the absence of slag and the high temperature required.
▼ If proper parameters are not set, then fusion problems can be faced.
▼ The welding gun is not designed for confined spaces.
▼ Some harmful radiation effects may be observed.
To sum it up, SMAW electrodes are solid with an external covering of flux, while FCAW electrodes are tubular with an inner flux core and an outer electrode shell. On the other hand, GMAW uses an externally supplied shielding gas, rather than flux.