plasma arc welding

Information about plasma arc welding

Plasma arc welding (PAW) 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. The key difference from GTAW is that in PAW, by positioning the electrode within the body of the torch, the plasma arc can be separated from the shielding gas envelope. The plasma is then forced through a fine-bore copper nozzle which constricts the arc and the plasma exits the orifice at high velocities (approaching the speed of sound) and a temperature approaching 20,000 °C.

PAW advantages

Plasma arc welding is an advancement over the GTAW process. This process uses a non-consumable tungsten electrode and an arc constricted through a fine-bore copper nozzle. PAW can be used to join all metals that are weldable with GTAW (i.e., most commercial metals and alloys). Several basic PAW process variations are possible by varying the current, plasma gas flow rate, and the orifice diameter, including:
  • Micro-plasma (< 15 Amperes)
  • Melt-in mode (15–400 Amperes)
  • Keyhole mode (>100 Amperes)
  • Plasma arc welding has a greater energy concentration as compared to GTAW.
  • A deep, narrow penetration is achievable; reducing distortion and allowing square-butt joints in material up to ½” (12 mm) thick.
  • Greater arc stability allows a much longer arc length (stand-off), and much greater tolerance to arc length changes.

PAW limitations

  • PAW requires relatively expensive and complex equipment as compared to GTAW; proper torch maintenance is critical
  • Welding procedures tend to be more complex and less tolerant to variations in fit-up, etc.
  • Operator skill required is slightly greater than for GTAW.
  • Orifice replacement is necessary.

Gases

At least two separate (and possibly three) flows of gas are used in PAW:
  • Plasma gas – flows through the orifice and becomes ionized
  • Shielding gas – flows through the outer nozzle and shields the molten weld from the atmosphere
  • Back-purge and trailing gas – required for certain materials and applications.
These gases can all be same, or of differing composition.

Key process variables

  • Current Type and Polarity
  • DCEN from a CC source is non standard
  • AC square-wave is common on aluminum and magnesium
  • Welding current and pulsing - Current can vary from 0.5 A to 1200 A; Current can be constant or pulsed at frequencies up to 20 kHz
  • Gas flow rate (This critical variable must be carefully controlled based upon the current, orifice diameter and shape, gas mixture, and the base material and thickness.)

Other plasma arc processes

Depending upon the design of the torch (e.g., orifice diameter), electrode design, gas type and velocities, and the current levels, several variations of the plasma process are achievable, including:
  • Plasma Arc Welding (PAW)
  • Plasma Arc Cutting (PAC)
  • Plasma Arc Gouging
  • Plasma Arc Surfacing
  • Plasma Arc Spraying

Plasma arc cutting (PAC)

When used for cutting, the plasma gas flow is increased so that the deeply penetrating plasma jet cuts through the material and molten material is removed as cutting dross. PAC differs from oxy-fuel cutting in that the plasma process operates by using the arc to melt the metal whereas in the oxy-fuel process, the oxygen oxidizes the metal and the heat from the exothermic reaction melts the metal. Unlike oxy-fuel cutting, the PAC process can be applied to cutting metals which form refractory oxides such as stainless steel, cast iron, aluminum, and other non-ferrous alloys.

See plasma cutter.

Suggested additional reading

American Welding Society, Welding Handbook, Volume 2 (8th Ed.)


Metalworking
Welding
  Arc welding: Shielded metal (MMA) | Gas metal (MIG) | Flux-cored | Submerged | Gas tungsten (TIG) | Plasma  
  Other processes: Oxyfuel | Resistance | Spot | Forge | Ultrasonic | Electron beam | Laser beam  
  Equipment: Power supply | Electrode | Filler metal | Shielding gas | Robot | Helmet  
  Related: Heat-affected zone | Weldability | Residual stress | Arc eye | Underwater welding  
  See also: Brazing | Soldering | Metalworking | Fabrication | Casting | Machining | Metallurgy | Jewelry  
Welding is a fabrication process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material (the weld puddle
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Gas tungsten arc welding (GTAW), also known as tungsten inert gas (TIG) welding, is an arc welding process that uses a nonconsumable tungsten electrode to produce the weld.
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electric arc is an electrical breakdown of a gas which produces an ongoing plasma discharge, resulting from a current flowing through normally nonconductive media such as air. A synonym is arc discharge. The phenomenon was first described by Vasily V.
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An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte or a vacuum). The word was coined by the scientist Michael Faraday from the Greek words elektron
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Sintering is a method for making objects from powder, by heating the material (below its melting point) until its particles adhere to each other. Sintering is traditionally used for manufacturing ceramic objects, and has also found uses in such fields as powder metallurgy.
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6, 5, 4, 3, 2, 1, 0, −1
(mildly acidic oxide)
Electronegativity 2.36 (scale Pauling)
Ionization energies 1st: 770 kJ/mol
2nd: 1700 kJ/mol
Atomic radius 135 pm
Atomic radius (calc.
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Shielding gases are inert or semi-inert gases that are commonly used in several welding processes, most notably gas metal arc welding and gas tungsten arc welding. Their purpose is to protect the weld area from atmospheric gases, such as oxygen, nitrogen, carbon dioxide, and water
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plasma is typically an ionized gas. Plasma is considered to be a distinct state of matter, apart from gases, because of its unique properties. "Ionized" refers to presence of one or more free electrons, which are not bound to an atom or molecule.
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Plasma cutting is a process that is used to cut steel and other metals (or sometimes other materials) using a plasma torch. In this process, an inert gas (in some units, compressed air) is blown at high speed out of a nozzle; at the same time an electrical arc is formed through
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Oxy-fuel welding (commonly called oxyacetylene welding or oxy welding or in the U.S. gas welding) and Oxy-fuel cutting are processes that use fuel gases and oxygen to either weld or cut metals.

There are a few differences between the two.
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Non-transferred arc plasma is a new process of high-temperature plasma arc cutting.

Materials commonly cut

  • Aluminium
  • Carbon steel
  • Ceramic
  • CNC
  • Cutting fluid
  • Metal
  • Metalworking
  • Stainless Steel
  • Plasma rifle

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Please help recruit one or [ improve this article] yourself. See the talk page for details.
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Welding is a fabrication process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material (the weld puddle
..... Click the link for more information.
Arc welding uses a welding power supply to create an electric arc between an electrode and the base material to melt the metals at the welding point. They can use either direct (DC) or alternating (AC) current, and consumable or non-consumable electrodes.
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Shielded metal arc welding (SMAW), also known as manual metal arc (MMA) welding or informally as stick welding, is a manual arc welding process that uses a consumable electrode coated in flux to lay the weld.
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Gas metal arc welding (GMAW), sometimes referred to by its subtypes metal inert gas (MIG) welding or metal active gas (MAG) welding, is a semi-automatic or automatic arc welding process in which a continuous and consumable wire electrode and a shielding gas are fed
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Flux-cored arc welding (FCAW) 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 electric current welding power supply.
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Submerged Arc Welding (SAW) is a common arc welding process. It requires a continuously fed consumable solid or tubular (flux cored) electrode. The molten weld and the arc zone are protected from atmospheric contamination by being “submerged” under a blanket of granular
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Gas tungsten arc welding (GTAW), also known as tungsten inert gas (TIG) welding, is an arc welding process that uses a nonconsumable tungsten electrode to produce the weld.
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This is a list of welding processes, separated into their respective categories.

Arc welding


Name Characteristics Applications
Atomic hydrogen welding Two metal electrodes in hydrogen atmosphere Historical
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Oxy-fuel welding (commonly called oxyacetylene welding or oxy welding or in the U.S. gas welding) and Oxy-fuel cutting are processes that use fuel gases and oxygen to either weld or cut metals.

There are a few differences between the two.
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Resistance welding refers to a group of welding processes that produce coalescence of faying surfaces where heat to form the weld is generated by the resistance of the welding current through the workpieces.
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Spot welding is a type of resistance welding used to weld various sheet metals. Typically the sheets are in the 0.5-3.0 mm thickness range. The process uses two shaped copper alloy electrodes to concentrate welding current and force between the materials to be welded.
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Forge welding is a welding process of heating two or more pieces metal and then hammering them together. Its use is ancient, being one of the least technologically complex methods of joining metals.
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Ultrasonic welding is an industrial whereby high-frequency ultrasonic acoustic vibrations are used to weld objects together, usually plastics, and especially for joining dissimilar materials.
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Electron beam welding (EBW) is a fusion welding process in which a beam of high-velocity electrons is applied to the materials being joined. The workpieces melt as the kinetic energy of the electrons is transformed into heat upon impact, and the filler metal, if used, also melts to
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Laser beam welding (LBW) 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.
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welding power supply is a device that provides an electrical current to perform welding. Welding usually requires high current (over 80 amps) and it can need above 12,000 amps in spot welding.
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An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte or a vacuum). The word was coined by the scientist Michael Faraday from the Greek words elektron
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A filler metal is a metal added in the making of a joint through welding, brazing, or soldering. Four types of filler metals exist—covered electrodes, bare electrode wire or rod, tubular electrode wire and welding fluxes.
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