For more than a hundred years, mankind has created many large or complex metallic structures. The process of joining two pieces of metal also known to us as welding had an important role in that effort. Over the years different needs created the foundation for developing many types of welding techniques. So, it is important for an engineer or fabricator to be aware of different types of welding processes in order to optimally perform their tasks. In this article, I will describe those techniques and I will mention their advantages and disadvantages. Let’s get to it.
- 1 Types of Welding Processes
- 1.1 Metal Arc Welding (MMA)
- 1.2 Carbon Arc Welding
- 1.3 Gas Metal Arc Welding
- 1.4 Gas Tungsten Arc Welding
- 1.5 Plasma Arc Welding
- 1.6 Submerged Arc Welding
- 1.7 Magnetically Impelled Arc Welding
- 1.8 Flux Cored Arc Welding
- 1.9 Atomic Hydrogen Welding
- 2 Conclusion
Types of Welding Processes
Metal Arc Welding (MMA)
Metal arc welding is also known as shielded metal arc welding (SMAW). A metal electrode is used in metal arc welding. An electric arc is developed between the metal electrode and the workpiece that needs to be joined. In this type of welding, a small area of the metal is melted near the joining place because the temperature of the electric arc rises a lot. The normal range of temperature in metal arc welding is from 2700˚C (4900°F) to 5500˚C (9900°F). In the same way, a small portion on the tip of the electrode is also melted and the drops of the molten metal pass to the base metal. Oxidation is the major defect that can cause issues in the welding and shielding for the oxidation is required. There is a flux coating on the electrode and it provides gaseous shielding to the oxidation.
How MMA Works
In metal arc welding, alternating current or direct current is used. When the alternating current is used, the arc is re-ignited after every half cycle because polarity is reversed in alternating current. This reverse in polarity causes instabilities in the arc and these instabilities can be removed with the help of stabilization agents that are used in the flux coating of the electrode. On the other hand, when it is the direct current that is used, there is a choice of use of a positive pole or negative pole. Positive polarity produces the highest temperature.
The voltage of arc ranges between 14 Volts to 45 Volts. The voltages of open circuits range from 50 Volts to 100 Volts. 30 Amperes to 500 Amperes of alternating current or direct current are usually used in this type of welding. There are slag-forming ingredients in the electrode that create a solid barrier between the liquid metal and the surrounding air during the cooling down process. Electrodes also contain some gas-forming components that help in the formation of carbon dioxide, carbon monoxide, or hydrogen around the arc. Some of the important materials that are used in the manufacturing of electrodes of metal arc welding are Carbonaceous materials, Silica, Titanium Oxide, Calcium fluoride, Ferro-silicon, Iron powder, etc. Iron Powder helps in increasing the rate of deposition and Ferro-silicon is de-oxidant.
In metal arc welding, the size of machines is dependent on the output rating and the output rating of machines in metal arc welding ranges from 150 Amperes to 1000 Amperes. Moreover, the rate of deposition ranges from two kilograms per hour to five kilograms per hour.
What Materials Can Be Welded With MMA
A large number of engineering alloys and metals can be joined with the help of metal arc welding. Electrodes made up of low carbon steel are used for welding steel alloys. Low carbon steel alloy electrodes are used for joining the steel alloys that have become brittle or hard state during cooling. Electrodes that are nickel rich are used for joining cast irons. Non-ferrous metals and alloys are welded with the help of electrodes made up of similar metals.
What Type of Joints Can Be Welded With MMA
There are five different types of joints that can be welded with MMA: corner (angle), lap joints, fillet (tee), butt, and edge joints. The most common types of welds that are created in metal arc welding are fillet joints.
Carbon Arc Welding
Carbon arc welding is a process that is used for joining metals by heating them and producing coalescences between a carbon electrode and metal workpiece. The electrode that is used in carbon arc welding is non-consumable. Carbon arc welding is the oldest welding technique but it is rarely used after the introduction of twin-carbon arc welding. A carbon electrode produces an electric arc with a temperature of more than 3000 ˚C. At this temperature, the separated metals melt. The separated metal creates a bond with each other at this temperature and they are welded together.
Sometimes, filled rods are used in carbon arc welding. The edge of the electrodes is placed inside the arc zone. Rod material is melted and the molten metal creates the weld pool.
Origins of This Process
Nikolay Benardos and Stanislaw Olszewski invented the technique of carbon arc welding in 1881. They suggested the name ‘Elekrogefest’ for this technique. The credits of developing the technique of carbon arc welding go to Sir Humphry Davy, who discovered the electric arc in 1800.
Carbon arc welding has been modified into Twin Carbon Arc Welding and two carbon electrodes are used in this type of welding as mentioned in the name of the technique. In this technique, the workpiece is not included in the circuit of welding. The benefit of this technique is that the welding arc can be taken from one workpiece to another and there is no need for extinguishing the arc.
Advantages and Disadvantages of Carbon Arc Welding
There are many advantages to carbon arc welding. The equipment for this type of welding is not costly and welding operation can be performed at cheap prices. In this type of welding, there is no requirement of skilled operation as the electrode is not consumed itself and the only requirement is to provide the arc to the welding zone. Furthermore, the process of carbon arc welding can be automated very easily because there are no complexities involved in this process. The last but not least advantage of carbon arc welding is that the workpiece is not distorted much during this process.
There are some disadvantages to this process also. The weld zone does not become much stable after the completion of the process and there exist many pores inside the weld zone. Apart from this, carbon electrodes that are used in this type of welding, leave carbides inside the seam. This fact decreases the quality of the welded zone.
Gas Metal Arc Welding
Gas Metal Arc Welding (GMAW) is a very high-speed process and very economic process that utilizes a metallic electrode for joining the metal components. Metal Inert Gas (MIG) welding is another name that is used for the same technique. In this technique, a continuous supply of consumable electrode is made sure to the base metal and metal of electrode is used as a filler metal. There is no coating or core used in electrode and electrode is completely bare. Shielding is required in every kind of welding because molten metal reacts very quickly with different components that are present in the atmosphere. In gas metal arc welding, the shielding is provided with the help of external gas. Mostly helium and argon are used for this purpose because they are well-known for their inertness. A large number of fumes can be developed during shield metal arc welding. These fumes are developed because of the direct consumption of electrode in the welding process and base metal does not take part in generating fumes. The equipment that is required for carrying out GMAW is the wire feeder, power cable, control cable, and constant source of voltage.
What Materials Can Be Welded With MIG
Gas metal arc welding is the best fit for welding different metals that have similar or close melting points. The metallurgical compatibility of GMAW is very high. In this technique, very close melting of both of the metals is done and close melting points of these metals assist in attaining it. Moreover, there are chances of development of cracks in the heat affective zone and metallurgical compatibility helps in the reduction of chances of development of cracks. Metallurgical compatibility also aids in developing the quality of corrosion resistance in the heat affective zone and it produces microstructures in the weld zone that increases the strength of joint.
As far as joining steel and aluminum alloys is concerned, gas metal arc welding is not suitable for this outcome. The reason behind it is the large gap between the melting point of these metals and iron is not compatible to join with aluminum because iron shows very limited solubility in aluminum. Moreover, iron forms brittle compounds and they are not compatible with the strength of the joint.
Advantages and Disadvantages of MIG
The first advantage of gas metal arc welding is that it can be used along the long stretches of metals because it is fed from a wire spool. It can be used for multiple ranges of metals and the only requirement is to change the filler metal wire according to the compatibility of base metals. Other advantages of GMAW include high rates of deposition, low process costs, high speeds of welding, higher rates of production, cheap consumables, high efficiencies of electrodes, low deposits of hydrogen, moderate level of skill is required and it is a slag less process. There is no requirement of cleaning up the flux or chipping flux.
Along with the advantages of this process, this process has some disadvantages also. The electrodes that are used in GMAW are very sensitive to the contaminants and there are higher risks of reaction between the consumable electrode and contaminants present in the environment. Therefore, a gas with a strong shielding effect is required for carrying out the gas metal arc welding. Contaminants in the environment can create porosity, the bad appearance of bead, and incomplete fusion of weld joints. There are risks involved in performing this type of welding in an outdoor environment. A slight wind can cause the shielding gas to blow away and it can allow the contaminants to react in the welding zone. Furthermore, like other welding processes, GMAW can be categorized as an open arc process and there are chances of harm for the welder and the bystanders. Proper shielding and safety of welder and bystanders are recommended during the process of GMAW because harmful ultraviolet rays are involved in this process. GMAW is a cheap welding process but the cost of the equipment required for this welding process is high. There are many electronic components involved in GMAW and maintenance costs of GMAW are higher in comparison with other welding techniques. Another major disadvantage of gas metal arc welding is that it is not a portable process and it requires a special setup. Therefore, GMAW can only be done at limited places with a lot of restrictions.
Gas Tungsten Arc Welding
Gas tungsten arc welding (GTAW) that is also known as tungsten inert gas (TIG) welding is a welding process that involves the production of the electric arc through a non-consumable tungsten electrode. Like the gas metal arc welding, gas tungsten arc welding also requires shielding from oxidation and other contaminants of the environment and it is done with the help of external inert gas. This external inert gas can be helium or argon. There is a requirement of filler metal for joining some special types of metals, although, gas tungsten arc welding can be carried out without the involvement of any filler metal. When the helium is used as an external inert gas for the sake of shielding, the process is known as heliarc welding. In tungsten arc welding, the electric arc is produced with the help of the supply of constant current welding powder. This welding powder is delivered around the arc and it is mixed in some highly ionized gas that creates metal vapors. These metal vapors are also known as plasma.
Gas tungsten arc welding is a suitable welding process for thin sheets of stainless steel and it is also compatible with the non-ferrous metals and their alloys. Copper, magnesium, and aluminum are mostly welded with the help of GTAW.
Advantages and Disadvantages
Gas tungsten arc welding is one of the most advanced techniques that are used in welding processes. It has many advantages over the other welding processes. In this process, the operator has a lot of controls as compared to the other techniques that are used for welding. These controls allow the formation of strong and high-quality welds. The heat-affected zone that is created in GTAW is very narrow because the operator is able to control the arc on pinpoint locations. Neither the slag is produced in this process nor is the flux required for carrying out gas tungsten arc welding. The absence of slag helps the operator in obtaining a clear image of the welding zone. Furthermore, there are no sparks produced in GTAW and metal does not spatter during the process. The only requirement for carrying out a successful GTAW process is the elimination of contaminants from the base metal. The production of fumes is very low in GTAW and it is very suitable for the safety of the operator. Safety is the major concern in carrying out any industrial process and GTAW is very safe from this point of view. Some metals are coated with nickel and zinc and involvement of zinc can cause the production of hazardous fumes but they can be controlled because their quantity is not considerable. Another advantage of GTAW is that it can be used for a variety of metals and alloys and it is compatible with a large number of metals than any other welding process. This process is best fit for welding the thin metals and it is also compatible with the welding of dissimilar metals.
Coming to the disadvantages of GTAW, GTAW has very slow travel speed as compared to the other arc welding processes. The rate of deposition is slower than the other welding techniques. There is a requirement of highly skilled operators for carrying out gas tungsten welding and a greater level of coordination between hand and eye is required during this process. Ultraviolet rays are harmful to the body and especially for eyes and GTAW is responsible for the development of more brighter ultraviolent rays than other techniques of welding. Costs involved in GTAW are much higher than the other welding processes. GTAW can be carried out in confined space but it requires proper ventilation because shielding gas displaces the oxygen. Therefore, proper ventilation is required for removing the fumes and gases. The use of an air-supplied respirator is highly recommended for the successful conduction of this process in the confined areas.
Plasma Arc Welding
Plasma arc welding (PAW) is a very similar technique to the previously discussed gas tungsten arc welding (GTAW). In this technique, like the other welding techniques, an electric arc is produced between the base metal and the electrode. The electrode can be made up of sintered tungsten but it is not a compulsory requirement and other metals can also be used in the electrode. The major difference between PAW and GTAW is that when the arc is placed on the pinpoint on base metal, the plasma arc and the envelope of shielding gas can be separated. A nozzle is used for delivering the plasma arc to the base metal and the velocity of the arc is very high. The velocity of the plasma arc leaving the orifice of the nozzle can approach the speed of sound. The temperature involved in this technique is considerably high and it can go higher than 28,000 ˚C. It is important to mention here that the plasma is a temporary state of the gas. The state of plasma is achieved through the ionization of gases with the help of an electric current. A mixture of ions is present in plasma and atoms of gases are broken down into electrons (-) and cations (+).
Equipment For Plasma Arc Welding
The equipment required for conducting the plasma arc welding is Plasma Torch, Power Supply, Shielding gases, Voltage Control, current limiting resistors, generators of high frequency and decay control for current and gases. Majorly, steel and aluminum can be welded through plasma arc welding.
Advantages and Disadvantages of Plasma Arc Welding
There are many advantages of plasma arc welding and they are mostly similar to the gas tungsten arc welding. The control of arc is a bit better than GTAW and it is because of the design of plasma torch. The freedom of observing and controlling the metal is a bit more than gas tungsten arc welding. The travel speeds of plasma in PAW are higher than GTAW and it is because of the higher concentrations of heat. The keyhole effect can be achieved in PAW because of the better concentration of heat and higher temperatures that are involved in this process. Most importantly, the heat-affected zone (HAZ) is much smaller than GTAW and it ensures the high strength and durability of weld.
Looking into the disadvantages, the cost of conducting the plasma arc welding is very high and the process has considerably higher set up costs than the other welding processes. Plasma welding requires high skills of operators and proper training of welders are required before conducting the plasma arc welding. The noises produced during this process are unsafe for the welders. The proper safety of welders is required during this process. The plasma torch that is involved in this process is a bit bulky and it requires special concentration for carrying out this process manually. However, PAW is not conducted manually and automated setups are usually used for the conduction of plasma arc welding.
Submerged Arc Welding
Submerged arc welding (SAW) is a common welding technique and it involves the formation of an arc between the workpiece and a continuously fed electrode. In this technique, the weld zone is protected with the help of powdered flux. The powdered flux creates a protective shield of gas and slag is used when there is a need for adding alloys to the weld zone. There is no requirement of shielding gas and it makes this process very easy. The electrode can be solid or made up of cored wire. Sometimes, the strip electrodes that are made up of sintered metal or sheet are also used in SAW. The flux is made by fusing the constituents into each other that results in the production of glassy slag and this glassy slag is converted into powder format that is directly used in this process. The flux also helps in stabilizing the arc and flux is responsible for the mechanical properties and shape of the bead.
Advantages and Disadvantages of SAW
There are many advantages of SAW as the welds that are made from this technique are reliable and sound. These welds are ready in no time and a very minute quantity of fumes are produced during this technique. Also, the emission of light in this process is very nominal and it is less dangerous for the operator. Submerged arc welding can be conducted in an outdoor environment as well as in the confined area. There is no restriction of indoor or outdoor areas on this process. The distortions produced in SAW are very small and deep weld penetrations can be obtained through this process. There is no requirement for the preparation of edges of metals in SAW. Some more advantages involve the welding of thick metals and recovery of more than 50% of flux.
There are some restrictions in conducting SAW also. The basic requirement for the conduction of SAW is a flat surface, otherwise, the metals cannot be welded properly. Granular flux and molten weld pool are involved in submerged arc welding and the welding can only take place in the positions of 1F, 2F, and 1G. Another disadvantage of SAW is that it is limited to circular vessels and pipes and handling of flux is difficult in submerged arc welding.
Magnetically Impelled Arc Welding
There are two different subtypes of magnetically impelled arc welding, magnetically impelled arc fusion welding (MIAF) or magnetically impelled arc butt welding (MIAB). The differences between these two techniques are negligible and both of them are used extensively for joining steel tubes and pipes.
MIAF initiates the arc with the help of a con-consumable electrode. In MIAB, an arc is created between the two joining metals. A pulsed power supply is required for carrying out both of the processes and metals are placed on a round spigot that is connected to that supply. The circuits are completed with the help of annular electrodes. There is no requirement of additional filler metal and arc is rotated along with the spigot until the metals are welded properly. The magnetic field is applied externally and an arc is drawn between the gaps of tubes.
It is important to mention here that the tubes are placed at some distance but they are properly aligned. The arc is only used for the proper heating of ends of the tube and after the proper heating of ends of tubes, they are forged together. In this way, a large quantity of molten metal is expelled and the solid bond is formed between the ends of two different tubes. The concepts of forging and removal of molten metal from the weld joint can categorize these processes as non-fusion processes.
Advantages and Disadvantages of MIAF
It is a fully automated process and it has vast applications in the automotive industry. The main advantages of MIAF and MIAB are that the components are not rotated and it helps in eradicating the problems that are related to the asymmetrical parts. The problems that are risen during friction welding can also be eradicated during this process. Further benefits of MIAF are that no resistors are used for the purpose of heating and only electric arc serves the heating purpose.
The disadvantages involve the high process costs, high set up costs, requirement of a skilled operator and slow travel speeds.
Flux Cored Arc Welding
Flux-cored arc welding (FCAW OR FCA) is a semi-automated or completely automated process of welding. A consumable tubular electrode is used in this process and flux is integrated with the electrode. There is a basic requirement of a constant supply of voltage or constant supply of welding current. The supply of welding current is not common and the supply of voltage is used instead of them.
Sometimes, the external shielding gas is also supplied depending upon the conditions, otherwise, flux is necessary for protecting the weld zone from contaminants. In this type of welding, both the gaseous flux and liquid slug are used for the protection of the weld zone. FCAW is an alternative of SMAW and it is extensively used in the construction industry.
Advantages and Disadvantages of FCAW
The basic advantage of FCAW is its portability and high welding speeds that allow it to be used extensively in the construction industry. Moreover, FCAW can be conducted in all positions if the compatible filler metal is used. The rate of deposition of FCAW is comparatively higher than SMAW. FCAW can be performed in an open environment because no shielding gas is required. Less skilled operators can perform FCAW and this advantage increases its workability as compared to SMAW and GTAW. There are very fewer chances of porosity and high metallurgical benefits can be obtained from FCAW. Furthermore, very less equipment is required for FCAW.
FCAW also comes up with some disadvantages such as the feed wire is irregular in FCAW. The gases are entrapped in the heat-affected zone and they are not able to leave the weld zone before the hardening of metal. This leaves the weld joints with considerable welding defects. Costly filler materials are required for conducting FCAW as compared to the other welding techniques that utilize filler material. Moreover, fumes are generated in large quantities that can affect the safety and visibility of the operator.
Atomic Hydrogen Welding
Atomic hydrogen welding (AHW) is very similar to GTAW and it has the addition of hydrogen shield around the arc. The electric arc breaks the hydrogen shielding and a sufficient amount of heat is obtained. Tungsten cannot be welded with other welding techniques and only AHW is capable of welding tungsten. There is no need for flux in this technique and arc is held between two electrodes of tungsten.
Different techniques and processes of welding are overlooked and discussed thoroughly. Hopefully, you have got the big picture and you are able to distinguish which process is better for a project. Feel free to check other articles on this website and comment on the article.