Welding fabrication is often confused by laymen with metal fabrication. Metal fabrication could be described as an umbrella term for different fabrication and modification processes, one of which is welding fabrication. Most steel structures, independent of their size, are usually rather complex and segments are welded together at every place where using bolts and screws is either impossible or detrimental to structural integrity. Welding is one of the key focuses of metal fabrication and its simplest definition is connecting multiple pieces of metal by exposing them to high temperatures, thus causing thermally induced fusion of two or more pieces.

 

Depending on the type of the materials used and the desired outcome, there are following types of welding: gas metal arc welding (also called MIG welding), tungsten inert gas (TIG welding), stick welding or shield metal arc welding (SMAW), and Gas/Oxy-Acetylene Welding and Cutting. All of the listed ways of welding require different levels of expertise on the behalf of the welder and all of them are limited in use by the type of material.

Metal Inert Gas Welding Fabrication (MIG)

MIG is actually the acronym standing for metal inert gas welding, the method originally aimed at welding non-ferrous metals such as aluminum, copper or zinc, that is now being used for steel welding as well. MIG welding is based on a wire feed technique, meaning that, during the welding process, the wire comes out of the handgun and unto the weld. The MIG handgun has several key parts; these include a power cable, a gas nozzle, and an electrode conduit. When the welder presses a control switch on the handgun, the shielding gas flow, the flow of electricity and the electrode wire feed are all initiated, which causes an electric arc to form between the electrode wire and the welding material. It is important to note that the shielding gas does not contribute to the forming of the electric arc. The electric arc forms specifically when the electrically charged electrode and the metal touch. Shielding is there to prevent external contamination of the weld. Usually, welders use a 75-25% or 90-10% mixture of argon and CO2 as shielding gas, but this can vary depending on the conditions; for example, pure helium or argon can be used for nonferrous welding, but they will not provide enough protection in the case of steel welding.

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The choice of the type electrode will depend on the type of material that is to be welded. Although all electrodes have traces of deoxidizing metals (aluminum, silicon, manganese or titanium), the material of the electrode, or the filler material as it is also called, will always correspond to welding fabrication material (aluminum electrodes for aluminum welding, copper electrodes for copper welding etc.). The thickness of the electrode will also depend on the type of material. Welding thin pieces of sheet metal require a .08 mm welding wire, and thicker metals, such as steel, for example, will require 1.2 mm metals. The same goes for the power of the welding machine. Welding material needs to be brought to a melting point in order to initiate fusion, and a 120 Amp power supply unit will not be able to generate enough power to melt a 1-inch thick steel bar.

MIG welding is widely used today for two main reasons. First of all, MIG welding is a very fast process and the productivity output, where possible to use MIG method, of course, is rather high. It is also a relatively simple form of welding fabrication that does not require too much skill. Which makes it easy to automate the welding process. This is why the majority of robotic welders on a factory floor are MIG robotic welders. For its simplicity, MIG welding is also easy to learn and it is the starting point for amateur welders in many cases, meaning that employers looking for MIG welders usually do not have too hard a time finding them and their wages are not that high.

 

Tungsten Inert Gas Welding (TIG)

The next welding process on the list is tungsten inert gas (TIG) welding. TIG is similar to MIG welding in the sense that both techniques use inert gasses, such as helium or argon, for protecting the weld from external conditions. The main differences are that in TIG welding, tungsten electrodes are used and welders need to be much more skillful to complete the weld. The reason why TIG is generally considered a better method is that tungsten filler materials are more flexible and can be used on many different types of metal or alloys. This flexibility in use comes from the fact that tungsten has a higher melting point than any other metal as it melts at 3,410 degrees Celsius. The type of materials that are most often welded using this technique are thin pieces of stainless steel, and non-ferrous metals such as magnesium, aluminum and copper alloys.

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TIG welders are, however, harder to find and they need to be very experienced in order to perform the welding fabrication process accurately as the welder needs to use both hands. Namely, in one hand, the welder needs to have a handgun out of which comes has and electricity for arch forming, while with the other hand they need to apply the filler material. This approach allows the operator to have much greater control over the whole welding process, but it is slower than competing ones. If the process is conducted by a weld skilled operator, the quality and endurance can be much greater than with other competing methods. The insistence here is on purity as all the welding components and materials used in the process need to be clean of any dirt, oil, moisture as these can cause weld porosity and eventually decrease the strength by which two pieces of metal are held together. More liquid impurities, such as grease or moist, can be removed with alcohol, while corroded surfaces can be brushed away with the steel brush before the process.

 

Stick Welding/Shield Metal Arch Welding (SMAW)

SMAW is one of the oldest welding processes and it is the one that many beginner welders opt for as there it does not require a lot of welding equipment, and said the equipment is also rather cheap. Although many DIY welders prefer this method, it still falls under the category of difficult welding methods. SMAW is also the dominant welding technique in repair and maintenance industry because of these properties.

SMAW is a manual welding process that utilizes consumable electrodes covered by a layer flux (a flowing chemical cleaning agent used in metallurgy) to form a weld. This welding process is initiated when the arch is formed between the electrode and the material that is to be welded. The power supply can provide either direct or alternate current for the weld. As the temperature rises, the flux melts from the electrode and it pours down onto the weld; the fumes from the melting flux serve as a shielding gas to the weld while the thin layer of slag (melted flux) provides a material barrier between the weld and the surroundings. The melting point of the electrodes used is around 3,600 degrees Celsius.

SMAW is a rather versatile welding process as there are dozens of different types of electrodes that can be used for many different types of material. The fact that it does not require a lot of equipment also contributes to the literal versatility as operators can easily relocate from one place to another. It owes this versatility to the fact that there is no need carry around a gas or wire feeder. This welding fabrication process is most often used to weld iron and steel, which also includes stainless steel, but it can be used for welding different copper alloys as well as aluminum and other non-ferrous metals. SMAW is rather extensively used in welding steel pieces for heavy steel constructions and in industrial welding fabrication works. The main drawback of this technique is that it makes it is difficult to use it for welding thin or sheet metal and it requires a very experienced operator to do the job properly in these scenarios. SMAW is less clean than the other methods as it leaves behind more waste that needs to be cleaned in order to guarantee the quality of the weld.

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Oxyacetylene welding

Oxyacetylene welding is a welding process that utilizes fuel gasses and oxygen to either cut or weld pieces of metal. This is one of the oldest welding methods (pioneered by French engineers as early as 1903) and it is slowly being made obsolete by advances made in the field of arc welding. Oxyacetylene welding finds application today mostly in metal-based artwork shops and similar smaller home-based metal welded fabrication units. The most usual practice in this method is to use high-temperature gas to bring two pieces of metal to the melting point and then hammered them together until they join while they are still in the molten state. Another way to weld two pieces of metal together by using oxyacetylene welding is to bring them to their boiling point and then at a filler material of the same type as the molten one. The filler material used, regardless of its composition, is called the welding rod. Oxyacetylene welding technique calls for the use of special welding handguns that mix acetylene and oxygen gases in order to produce a small, but very intense, flame which is burning at the temperature of some 3,500 degrees Celsius; this is the highest temperature reached in gaseous welding fuels and it is twice as higher than the melting point of most metals. This is another method that is relatively easy to master, but the drawback for DIY welders is that it requires a lot of equipment.

The oxyacetylene gas mixture can also be used for cutting metals, and most torches used today have the function that enables the switch from the welding mode to the cutting mode. The technical difference here is that the gas mixture needs to be richer in oxygen as this results in higher flame temperature. This consequently causes the parent metal to burn away much faster, resulting in a rather narrow cut in the material. When the process is performed manually, oxyacetylene gas can easily cut through steel material thick 1.5 mm, while profile cutting can go through steel as much 10 centimeters thick.

Although oxyacetylene welding fabrication is not difficult to learn, there are several key points that need to be addressed regarding the safety of the welder. The gas and its fumes can be dangerous in higher concentrations and that is why it is important for the room where the welding occurs to be well ventilated. Acetylene gas and fumes cannot directly cause injuries or death, but prolonged exposure can cause symptoms such as dizziness or disorientation which is dangerous when working with flames hotter than 3,000 degrees Celsius. Another reason why oxyacetylene welding is becoming obsolete is the instability of the acetylene gas. Acetylene is very inflammable, and heavier than air so leaks are difficult to discover but can have grave consequences to both the property and the operator. It is also not recommended to use up more than one-seventh of the capacity of the cylinder in an hour as this may cause more gas to leak into the hose and the torch.

These are some of the most popular welding fabrication techniques used today. However, there are many more nuances and details that need to be addressed in these techniques, as well as many more different techniques that are used in various industries and with various materials.

Sources:

http://www.wikipedia.com

http://www.weldingtypes.net/

http://www.thefabricator.com/article/arcwelding/guidelines-for-tungsten-electrodes

http://diy-welder.com/MIG-TIG-ARC.shtml

http://earlbeck.com/types-of-welding.html

http://www.weldersuniverse.com/Oxy_gas_rods.html