Fusion welding joins two pieces of metal by melting them with a filler metal and flux. Types include arc, electric resistance, oxy-fuel, thermite, and laser beam welding. Each has unique advantages and limitations.
Fusion welding is the process used in metalworking to join or fuse two pieces of metal causing the metal to reach its melting point. The process requires the use of a filler metal, supplied by the electrode or a wire, and a flux, which protects the molten weld metal from the harmful effects of the atmosphere. There are different types of fusion welding which are used for various applications. Common examples of this welding process include arc welding, electric resistance welding, oxy-fuel welding, and thermite welding.
Arc welding is a form of fusion welding that uses electricity, supplied by a welding power supply, to produce an electric arc between an electrode and the pieces of metal being joined. Arc welding is a popular choice in both industry and the home workshop due to its low initial costs and relatively low maintenance costs. The arc welder’s electric arc is highly focused, making it possible to automate the welding process and earning a place for arc welding equipment on many assembly lines.
Similar to arc welding, electric resistance welding uses electricity to create the heat needed to weld. In an electric resistance welding setup, the electrodes rest on both sides of the workpieces to be welded together. Pressure is applied to push the two pieces together and make electrical contact. This process is very limited in the size of material that can be worked with and the cost of the equipment is often prohibitive for industrial applications.
Oxy-fuel welding is one of the best known forms of fusion welding. This form of weld can incorporate a variety of fuel gases, including acetylene, liquid petroleum, hydrogen, propane, natural gas, or propylene, but requires the addition of oxygen to be considered oxy-fuel welding. The most common fuel gas choice is acetylene. Using acetylene gas and pure oxygen, oxy-fuel welding equipment can produce flame temperatures of 6,330 degrees Fahrenheit (3,500 degrees Celsius). This flame is hot enough to melt most industrial metals.
Thermite welding is another fusion welding process that uses intense heat and flame to bring the design metal to its melting point. Using red iron oxide and aluminum powder, thermite welding is able to join railway rails. This powerful form of welding produces strong welds in a short time. In the example provided of railroad track joining, the complete repair, including installation and finishing time, takes approximately one hour before a train can use the rail system.
Laser beam welding is a form of fusion welding that is sometimes used in the manufacture of automobiles and other mass-produced metal products. By creating a very precise and concentrated heat source, this welding process can penetrate deeply with a very small area affected by the heat. While this capability is preferable in many applications, the prohibitive costs of laser beam welding equipment leave this form of welding largely relegated to a few large industries.
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