Processes | Description |
Soldering
| - It is a process in which two or more items (usually metal) are joined together by melting and putting a filler metal (solder) into the joint, the filler metal having a lower melting point than the adjoining metal.
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Brazing
| - It is a metal-joining process in which two or more metal items are joined together by melting and flowing a filler metal into the joint, the filler metal having a lower melting point than the adjoining metal.
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Induction Welding | - It is a form of welding that uses electromagnetic induction to heat the workpiece.
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Explosion Welding (EXW)
| - It is a solid state (solid-phase) process where welding is accomplished by accelerating one of the components at extremely high velocity through the use of chemical explosives. Explosion welding or bonding is a solid state welding process that is used for the metallurgical joining of dissimilar metals. The process uses the forces of controlled detonations to accelerate one metal plate into another reacting an atomic bond.
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Friction Welding (FRW) | - It is a solid-state welding process that generates heat through mechanical friction between workpieces in relative motion to one another, with the addition of a lateral force called "upset" to plastically displace and fuse the materials.
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Ultrasonic Welding | - It is an industrial technique whereby high-frequency ultrasonic acoustic vibrations are locally applied to workpieces being held together under pressure to create a solid-state weld. It is commonly used for plastics, and especially for joining dissimilar materials. In ultrasonic welding, there are no connective bolts, nails, soldering materials, or adhesives necessary to bind the materials together.
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Shielded Metal Arc Welding (SMAW) | - It is also known as manual metal arc welding (MMA or MMAW), flux shielded arc welding or informally as stick welding, is a manual arc welding process that uses a consumable electrode covered with a flux to lay the weld.
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Submerged Arc Welding (SAW) | - It is a common arc welding process. The first patent on the submerged-arc welding (SAW) process was taken out in 1935 and covered an electric arc beneath a bed of granulated flux.
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Gas Metal Arc Welding (GMAW) | - It is sometimes referred to by its subtypes metal inert gas (MIG) welding or metal active gas (MAG) welding, is a welding process in which an electric arc forms between a consumable wire electrode and the workpiece metal(s), which heats the workpiece metal(s), causing them to melt, and join.
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Flux-Cored Arc Welding (FCAW or FCA) | - It is a semi-automatic or automatic arc welding process. FCAW requires a continuously-fed consumable tubular electrode containing a flux and a constant-voltage or, less commonly, a constant-current welding power supply.
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Electrogas Welding (EGW) | - It is a continuous vertical position arc welding process developed in 1961, in which an arc is struck between a consumable electrode and the workpiece. A shielding gas is sometimes used, but pressure is not applied. A major difference between EGW and its cousin electroslag welding is that the arc in EGW is not extinguished, instead remains struck throughout the welding process. It is used to make square-groove welds for butt and t-joints, especially in the shipbuilding industry and in the construction of storage tanks.
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Gas Tungsten Arc Welding (GTAW) | - It also known as tungsten inert gas (TIG) welding, is an arc welding process that uses a non-consumable tungsten electrode to produce the weld.
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Plasma Arc Welding (PAW) | - It is an arc welding process similar to gas tungsten arc welding (GTAW). The electric arc is formed between an electrode (which is usually but not always made of sintered tungsten) and the workpiece.
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Stud Welding | - It is a technique similar to flash welding where a fastener or specially formed nut is welded onto another metal part, typically a base metal or substrate. The fastener can take different forms, but typically fall under threaded, unthreaded or tapped. The bolts may be automatically fed into the spot welder.
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Projection Welding | - It is an electric resistance welding process that uses small projections, embossments, or intersections on one or both components of the weld to localize the heat and pressure.
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Flash Welding | - It is a type of resistance welding that does not use any filler metals. The pieces of metal to be welded are set apart at a predetermined distance based on material thickness, material composition, and desired properties of the finished weld.
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Upset welding (UW)/ Resistance Butt Welding | - It is a welding technique that produces coalescence simultaneously over the entire area of abutting surfaces or progressively along a joint, by the heat obtained from resistance to electric current through the area where those surfaces are in contact. Pressure is applied before heating is started and is maintained throughout the heating period. The equipment used for upset welding is very similar to that used for flash welding. It can be used only if the parts to be welded are equal in cross-sectional area. The abutting surfaces must be very carefully prepared to provide for proper heating. The difference from flash welding is that the parts are clamped in the welding machine and force is applied bringing them tightly together. High-amperage current is then passed through the joint, which heats the abutting surfaces. When they have been heated to a suitable forging temperature an upsetting force is applied and the current is stopped. The high temperature of the work at the abutting surfaces plus the high pressure causes coalescence to take place. After cooling, the force is released and the weld is completed.
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Percussion Welding (PEW) | - It is a type of resistance welding that blends dissimilar metals together. Percussion welding creates a high temperature arc that is formed from a short quick electrical discharge. Immediately following the electrical discharge, pressure is applied which forges the materials together. This type of joining brings the materials together in a percussive manner. Percussion welding is similar to flash welding and upset welding but is generally considered to be more complex. It is considered to be more complex because it uses an electric discharge at the joint, followed by pressure being applied to join the materials together. Percussion welding is used to join dissimilar metals together, or used when flash is not required at the joint. Percussion welding is used on materials that have small cross sectional areas. Advantages of using percussion welding types include a shallow heat affected zone, and the time cycle involved is very short. Typical times can be found to be less than 16 milliseconds.
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High Frequency (HF) Welding or Radio Frequency (RF) Welding | - It is the joining of materials by supplying HF energy in the form of an electromagnetic field (27.12 MHz) and pressure to the material surfaces to be joined. A generator produces the energy. The tool used to supply the energy is called an electrode. The electrical energy causes the molecules within the material to start moving, which generates heat that causes the material to soften and thereby fuse together. No outside heat is applied. It is instead generated within the material. After cooling the welded surface under maintained pressure, the material is fused and a weld has been created. The weld seam can be at least as strong as the surrounding material – or even stronger.
- A high frequency coil introduces current into the tube ahead of the squeeze rolls. This current is concentrated on the edges of the strip in the V and resistance heats a narrow zone at the edges to the welding temperature. The squeeze rolls consolidate the weld by expelling any melted material and contaminants and forming a small upset bead inside and outside the tube. These beads may be immediately scarfed from the tube to give a smooth surface. Thin wall steel tube may be welded at up to a few hundred m/min.
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Diffusion Welding (DFW) | - It is a solid state welding process by which two metals (which may be dissimilar) can be bonded together. Diffusion involves the migration of atoms across the joint, due to concentration gradients.
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Oxy-Fuel Welding | - It is commonly called oxyacetylene welding, oxy welding, or gas welding. It is a processes that use fuel gases and oxygen to weld and cut metals, respectively. French engineers Edmond Fouché and Charles Picard became the first to develop oxygen-acetylene welding in 1903. Pure oxygen, instead of air, is used to increase the flame temperature to allow localized melting of the workpiece material (e.g. steel) in a room environment. A common propane/air flame burns at about 2,250 K (1,980 °C; 3,590 °F), a propane/oxygen flame burns at about 2,526 K (2,253 °C; 4,087 °F) and an acetylene/oxygen flame burns at about 3,773 K (3,500 °C; 6,332 °F). Oxy-fuel is one of the oldest welding processes, besides forge welding. Still used in industry, in recent decades it has been less widely utilized in industrial applications as other specifically devised technologies have been adopted. It is still widely used for welding pipes and tubes, as well as repair work. It is also frequently well-suited, and favored, for fabricating some types of metal-based artwork. As well, oxy-fuel has an advantage over electric welding and cutting processes in situations where accessing electricity (e.g., via an extension cord or portable generator) would present difficulties; it is more self-contained, and, hence, often more portable. In oxy-fuel welding, a welding torch is used to weld metals. Welding metal results when two pieces are heated to a temperature that produces a shared pool of molten metal. The molten pool is generally supplied with additional metal called filler. Filler material depends upon the metals to be welded.
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Oxy-Fuel Cutting | - In oxy-fuel cutting, a torch is used to heat metal to its kindling temperature. A stream of oxygen is then trained on the metal, burning it into a metal oxide that flows out of the kerf as slag. Torches that do not mix fuel with oxygen (combining, instead, atmospheric air) are not considered oxy-fuel torches and can typically be identified by a single tank (oxy-fuel cutting requires two isolated supplies, fuel and oxygen). Most metals cannot be melted with a single-tank torch. As such, single-tank torches are typically used only for soldering and brazing, rather than welding.
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Electroslag Welding (ESW) | - It is highly productive, single pass welding process for thick (greater than 25 mm up to about 300 mm) materials in a vertical or close to vertical position. (ESW) is similar to electrogas welding, but the main difference is the arc starts in a different location.
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Electron Beam Welding (EBW) | - It is a fusion welding process in which a beam of high-velocity electrons is applied to two materials to be joined. The workpieces melt and flow together as the kinetic energy of the electrons is transformed into heat upon impact.
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Laser Beam Welding (LBW) | - It is a welding technique used to join multiple pieces of metal through the use of a laser. The beam provides a concentrated heat source, allowing for narrow, deep welds and high welding rates. The process is frequently used in high volume applications, such as in the automotive industry.
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Thermite Welding | - It was a step forward for joining rails. A thermite weld in progress. Exothermic welding, also known as exothermic bonding, thermite welding (TW), and thermit welding, is a welding that employs molten metal to permanently join the conductors.
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Submerged Arc Strip Cladding | - Although two types of process exist most commonly used process is Submerged Arc Strip cladding. Generally applications of the submerged arc process make use of single multi wire systems using round wires, electrodes in the form of a strip are often used for cladding purpose.
- Strips are usually 0.5mm thick, the commonest strip width being 60mm, but wider strips eg.100mm also can be used without any loss of quality. The advantage of strip cladding is that penetration is low, particularly with DC electrode negative polarity, and deposition rate is relatively high.
- Modern fluxes designed for strip cladding has greater current tolerance than earlier types and use of current is up to 1200 amperes with austenitic stainless strips gives deposition rates of up to 22kg/hr. with DC electrode positive polarity and 32 kg/hr with DC electrode negative.
- Inconel can also be deposited and, provided the flux is low silica type and the Inconel strip used contains 2-3% Nb, good quality crack free deposits can be obtained. Monel, Aluminium, bronze, nickel and 13% Cr strips have also been successfully used as strip cladding electrodes. Good electrical contact between the strip and feed nozzle is essential.
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Electro Slag Strip Cladding | - The origin of ESW strip cladding is from the SAW Strip cladding process which when compared has high deposition rates. It relates the resistance welding processes and is based on the ohmic resistance heating of a molten electrically conductive slag. The heat generated by molten slag melts the surface of the base material and the edge of the strip is submerged in the slag and flux. The penetration achieved here is less than that of SAW cladding process. The temperature of the molten slag is about 2300ºC. ESW uses higher welding currents when compared to SAW.
- Electro slag welding is initiated by starting an arc between the electrode and base metal. The heat melts the added granulated welding flux. With the formation of sufficiently thick molten slag layer all arc action stops. The passage of welding current through the conductive slag leads to ohmic heating of the consumable, base metal and flux. The electromagnetic action leads to vigorous stirring of molten slag. Heat diffuses through the entire cross section being welded.
- The electrodes used arc wire or strips. As there is no continuous arc ESW produces 50% less dilution when compared to SAW. ESW has been used in similar application as SAW with far superior results. They are only partially covered by specifications like ASW A5.13 surfacing welding rods and electrodes. A5-21 covers tungsten carbide alloys and other alloys in composite form.
- ESW uses higher welding currents when compared to SAW. The penetration is lower for ESW when compared to SAW. ESW strip surfacing reduces dilution upto 50% when compared to SAW strip surfacing for same heat input with significantly higher deposition rate.
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