Laser beam welding is a welding process which produces coalescence of materials with the heat obtained from the application of a concentrated coherent light beam impinging upon the surfaces to be joined.

The focused laser beam has the highest energy concentration of any known source of energy. The laser beam is a source of electromagnetic energy or light that can be projected without diverging and can be concentrated to a precise spot. The beam is coherent and of a single frequency.

Producing a laser beam is extremely complex. The early laser utilized a solid-state transparent single crystal of ruby made into a rod approximately an inch in diameter and several inches long. The end surfaces of the ruby rod were ground flat and parallel and were polished to extreme smoothness.

The laser can be compared to solar light beam for welding. The laser can be used in air. The laser beam can be focused and directed by special optical lenses and mirrors. The laser can operate at considerable distance from the work piece.

When using the laser beam for welding the electromagnetic radiation impinges on the surface of the base metal with such a concentration of energy that the temperature of the surface is melted and volatilized. The beam penetrates through the metal vapor and melts the metal below. One of the original questions concerning the use of the laser was the possibility of reflectivity of the metal so that the beam would be reflected rather than heat the base metal. It was found, however, that once the metal is raised to its melting temperature the surface conditions have little or no effect.

The welding characteristics of the laser and of the electron beam are similar. The concentration of energy by both beams is similar, with the laser having a power density in the order of 106 watts per square centimeter. The power density of the electron beam is only slightly greater. This is compared to a current density of only 104 watts per square centimeter for arc welding.

Laser beam welding has a tremendous temperature differential between the molten metal and the base metal immediately adjacent to the weld. Heating and cooling rates are much higher in laser beam welding than in arc welding, and the heat-affected zones are much smaller. Rapid cooling rates can create problems such as cracking in high carbon steels.

The laser beam has been used to weld carbon steels, high strength low alloy steels, aluminum, stainless steel and titanium. Laser welds made in these materials are similar in quality to welds made in the same materials by electron beam process.

Thermite welding is the process of igniting a mix of high energy materials, also called thermite, that produce a metallic slag that is poured between the working pieces of metal to form a joint. It was developed by Hans Goldschmidt around 1895.

Commonly utilizing the composition of 5 parts iron oxide red (rust) powder and 3 parts aluminium powder ignited at high temperatures. A violent reaction occurs that produces through reduction and oxidation a white hot iron slag and vaporous aluminium oxide. This form of welding is still widely used to weld railway rails. This form of welding is also in use today for example for quick fixes on ship hull punctures and the likes. Weld quality is low due to the fact of low to nil carbon content in the filling metal and low heat penetration into the joining metals. This method is usually used in conjunction with oxyacetylene flame to create a good fusion with the working pieces of metal.

From Wikipedia, the free encyclopedia

Thermite is a pyrotechnic composition of aluminium powder and a metal oxide which produces an aluminothermic reaction known as a thermite reaction. It is not an explosive, but can create short bursts of extremely high temperatures focused on a very small target for a short period of time.

Metals are capable of burning under the right conditions similar to the combustion process of wood or gasoline. In fact, rust is the oxidation of steel or iron at very slow rates. Thermite is a process in which the correct mixture of metallic fuels are combined and ignited. Ignition itself requires extremely high temperatures.

The aluminium is oxidized by the oxide of another metal, most commonly iron oxide (rust). The products are aluminium oxide, free elemental iron, and a large amount of heat. The reactants are commonly powdered and mixed with a binder to keep the material solid and prevent separation.

The reaction is used for thermite welding, often used to join rail tracks. Other metal oxides can be used, such as chromium oxide, to generate elementary metal. Copper thermite, using copper oxide, is used for creating electric joints in a process called cadwelding. Some thermite-like mixtures are used as pyrotechnic initiators such as fireworks.