Plasma arc welding


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.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 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.

Process Variables

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.

Materials

The parts are usually of conductive metals and alloys ranging from 3 mm in thickness to .25 in in thickness. Anything less than the 3 mm may fail due to lack of material and anything more than .25 in. in thickness may experience a failure due to an instability within the weld.

Key process variables

* Current Type and Polarity
* DCEN from a CC source is 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. Since PAC was introduced by Praxair Inc. at the American Welding Society show in 1954, many process refinements, gas developments, and equipment improvements have occurred.

See plasma cutter.

External links

* http://www.robots4welding.com/applications.php?app=plasma+arc+welding

uggested additional reading

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


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • plasma arc welding — plasma arc welding, arc welding using the extremely high temperatures of a plasma jet to weld metal …   Useful english dictionary

  • Plasma-arc welding — Plasma arc welding. См. Плазменно дуговая сварка. (Источник: «Металлы и сплавы. Справочник.» Под редакцией Ю.П. Солнцева; НПО Профессионал , НПО Мир и семья ; Санкт Петербург, 2003 г.) …   Словарь металлургических терминов

  • 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.… …   Wikipedia

  • Carbon arc welding — (CAW) is a process which produces coalescence of metals by heating them with an arc between a nonconsumable carbon (graphite) electrode and the work piece. It was the first arc welding process ever developed but is not used for many applications… …   Wikipedia

  • Gas tungsten arc welding — TIG welding of a bronze sculpture Gas tungsten arc welding (GTAW), also known as tungsten inert gas (TIG …   Wikipedia

  • Gas metal arc welding — RMD redirects here. RMD may also refer to IRA Required Minimum Distributions. Gas metal arc welding …   Wikipedia

  • Shielded metal arc welding — (SMAW), also known as manual metal arc (MMA) welding, flux shielded arc welding …   Wikipedia

  • 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 ) that cools to… …   Wikipedia

  • Plasma cutting — This article is about the common manufacturing process. For various fictional weapons, see plasma rifle and directed energy weapon. Plasma cutting is a process that is used to cut steel and other metals (or sometimes other materials) using a… …   Wikipedia

  • Arc — may refer to: Computing and gaming*Arc (programming language), a Lisp dialect in development by Paul Graham *.arc, a file extension for archive files *arc, the command line interface for ArcInfo *Arc System Works, a video game… …   Wikipedia


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.