What is plasma welding? 👨‍🏭


The plasma arc welding process, also known as PAW (Plasma Arc Welding), is one in which the fusion of metals is caused by an electric constrictor arc, established between a tungsten electrode and the workpiece. The Plasma that names this process refers to the gas that is ionized.

As with the TIG process, the tungsten electrode is not consumable. The arc is called constricted because it is limited by a nozzle that restricts the diameter of the arc and increases the intensity of the heat source.

This arc is surrounded by a protective atmosphere provided by two gas streams. First, the plasma gas surrounds the non-consumable tungsten electrode, forming the core of the plasma arc. This gas, which is normally argon, leaves the constrictor nozzle in the form of a highly heated jet, called plasma.

The second is the shielding gas that prevents contamination of the weld pool. This gas passes through an external nozzle, concentric to the constrictor nozzle, and works as a shield; this gas may be inert or a mixture of inert gases.

Differences between TIG and Plasma

Plasma welding is a very similar process to TIG. Basically, it is a modification aimed at increasing productivity.

The plasma arc welding process is very similar to the TIG process in that it uses non-consumable electrodes and inert gases. The differences are in the type of torch and electric arc voltage used, in addition to the resources required by the power source (also known as a welding machine).

It is important to note that the two processes present regions with the same maximum temperatures; however, the constriction of the arc causes a substantial change in the heat concentration on the surface of the part, making it more favorable to the welding process.


The plasma arc process is used to join most metals that can be welded using the TIG process. Thus, carbon steels, alloy steels, stainless steels, refractory alloys, titanium alloys are conveniently welded by this process.

It can also be applied in thicknesses from 0.02 to 6mm, economically. For thicknesses from 2.4 to 6 mm, the welding technique known as "keyhole" is used.

However, the largest industrial application of the plasma welding process resides in the manufacture of stainless steel equipment, with medium thickness plates (3 to 8 mm) and those that require long strands, such as tanks and reactors for chemical and beverage industry.

The application in the aerospace industry, in the welding of special aluminum alloys, is also reported. Although less common, the Plasma process can be applied to carbon steel joints, such as welding the upper part of shock absorbers intended for the automotive industry.

As other application examples, one can mention the manufacture of radiators, the welding of critical points in car engines and the welding of electrical components, such as sheets for transformers and alternators.

The field of application of this process extends to the welding of compressors and other components for the white goods, in addition to axles and structural components for motor vehicles, which would include the making of so-called “tailored blanks”.

The term “tailored blanks” refers to panels formed from several steel sheets welded together as a “patchwork quilt” (each part may have different thickness and mechanical properties).

In general, the application of the Plasma process becomes more common in high production welds, when the cost-related disadvantages are outweighed by the intrinsic advantages of the process.


The advantages of the plasma arc welding process, in relation to the TIG process or other conventional welding processes, are: higher energy concentration and current density, consequently, lower distortions, higher welding speeds and greater penetrations; greater arc stability at low current levels, allowing the welding of thin thicknesses, from 0.05mm; the arc is more homogeneous and of greater extension, allowing better operational visibility, greater constancy of the weld pool and less sensitivity to variations in arc length; less likelihood of bead contamination by tungsten inclusions and electrode contamination by filler material.

One of the great advantages of the Plasma process, especially when it comes to logistics (purchase, transport and material stock operations), is the possibility of eliminating the use of wire (filler metal).

Due to the intensity and concentration of the arc (heat), it is possible to weld sheets up to 10 mm thick in a single pass. The Plasma process is also credited with greater tolerance to arc length variation (torch distance from the part to be welded) and greater fusion thermal efficiency, resulting in lower volume welds with lower levels of residual tensions or distortions.

These advantages, together with other positive characteristics, have put the plasma welding process in direct competition with other conventional processes, not only with TIG, but even with MIG/MAG, in several applications.


It is important to point out that this process has an inherent operational complexity. There is a requirement for better joint preparation (lower tolerance) and greater mastery of parameter adjustment. The lower tolerance requirement in the preparation and fixing of the joint parts directs this process towards automated lines, as seen in the Figure below.

Another disadvantage is the limited supply of plasma welding systems and the relatively high cost of these equipment, especially when compared to the TIG process.


The disadvantages of the plasma arc welding process are:
  • High cost of equipment (two to five times more than TIG);
  • Expensive and more frequent torch maintenance;
  • Higher consumption of gases;
  • Demand for higher qualification of the workforce.

Important points

The critical points for the diffusion of plasma welding are due, in part, to the lack of consolidated information on the regulation of welding parameters and on the materials that are actually weldable.

However, despite being known for years through classical literature, the Plasma process still does not find great application in the industrial environment, especially in countries where industrial development is still growing, such as Brazil. However, in Germany this process has been widely used in specific applications because it is more efficient than other arc processes.

One of the explanations for the initial failure of plasma welding may be the way in which the process was introduced to the market; the expression “Plasma Welding” brought to the minds of users a complex process with high added technology. From a “marketing” point of view, using the word Plasma to describe a modification of the TIG process may have hurt its receptivity.

The Plasma process could perhaps have been better received in the market if it had been presented as a new version of the TIG process and not as another process. When introducing a new process, it is important to relate it to the end-user needs.

Equipment manufacturers should have disclosed the application potential of the new process and the advantages over conventional processes. In the history of the Plasma process, there was a tendency on the part of equipment suppliers to provide a lot of information about how the process worked and little information about what the process was capable of doing.


Plasma is an important element in plasma arc welding. It is customary to think of three states of matter: solid, liquid and gas. The best-known element, water, has three physical states: ice, water and steam; the basic difference between these three states is the energy level they are at.

When energy in the form of heat is added to ice, it turns into water, which, when subjected to more heat, will vaporize. If more energy is added, some of its properties, such as temperature and electrical characteristics, will be modified substantially. This process is called ionization, ie the creation of free electrons and ions between the atoms of the gas.

When this happens, the gas becomes an electrically conductive plasma, that is, the free electrons transmit electric current. This is why plasma is considered the fourth state of matter.
Some of the principles applied to the conduction of current through a metallic conductor are also applied to plasma. For example, when the section of a metallic conductor subjected to an electric current is reduced, the resistance increases and it becomes necessary to increase the voltage to obtain the same number of electrons crossing this section; as a result, the temperature of the metal increases.

The same fact can be observed in plasma: the smaller the section, the higher the temperature.

Plasma arc welding is done through two working techniques, which are fusion and the so-called "keyhole" technique.


Fusion welding, similar to other arc processes, is generally employed in manual welding with one or more passes, with low welding currents and low gas flow. It is possible to add filler metal to the weld pool, in the form of a rod.

"Key hole”

In the "keyhole" technique, the plasma jet makes a small hole in the joint region; this hole is extended with the movement of the torch and, during the displacement, the metal molten by the arc moves around the plasma, forming the weld pool; this closes the hole in the region and solidifies, welding the joint.

Why argon?

Argon has been preferred in low current welding because of its higher ionization potential. It promotes better cleaning of the reactive metal oxide layers and facilitates the opening of the electric arc. It is used in working with carbon steels, high strength steels and reactive metals such as titanium and zirconium.

Other inert gases such as pure helium or mixed with argon can be applied, but these require higher voltages to strike the arc. The use of helium (He) develops more energy in the plasma, so the orifice nozzle cooling must be very efficient.
Mixtures of argon and hydrogen are also used for plasma, with the advantage that hydrogen has a reducing character and the ability to increase the arc composition, reducing the risk of undercuts and increasing welding speed.

Welding equipment

Plasma arc welding can be done manually or by machines, with some adaptations. Both processes are widely used and can be used in any position. The equipment consists of power source, arc striking system, plasma welding torch, gas cylinders and control system.

Power supply

The energy source used is constant current, which can be a rectifier, generator or inverters, using direct current and direct polarity. Plasma welding sources differ from cutting ones, because when cutting the equipment, the no-load voltage of the equipment must be greater than 200V. Sources with no-load voltage between 65V and 80V can be adapted for welding with the placement of pilot arc opening systems, pre and post flow.

High frequency generator

To open the arc, a high frequency generator is used to establish a pilot arc. In the case of working with transferred arc, the pilot arc is generally used, which requires a low-capacity auxiliary energy source for power.


The torch serves to fix the tungsten electrode and direct the electric arc; is provided with a handle for handling the welder, a set of clamps for fixing the electrode, conduits for passing gas and cooling water, a copper nozzle with an orifice for constriction of the electric arc and a ceramic nozzle for isolation and operator protection.

In a plasma torch, the electrode tip is collected in a nozzle, through which the plasma flows. The gas ionizes when passing through the electric arc forming plasma, which is the dissociation of molecules into atoms and these into ions and electrons.

The heated gas inside the nozzle undergoes a huge increase in pressure and, as it has to exit through a small orifice, it acquires high speeds, on the order of 6 km/s, accentuating the phenomenon of dissociation.

Some torches have only one central hole for gas and arc to pass through; others have other holes for the passage of auxiliary gas, allowing higher welding speeds.

Gas cylinders

Gas cylinders are the sources of ionizable gas and shielding gas; are provided with pressure and flow regulators and hoses. The gas flow control must be very precise, as this is an important variable in the process.

Control system

The control system exists to allow the adjustment of welding variables and the activation of equipment and auxiliary devices, when it comes to mechanized welding. These devices are similar to those used in TIG welding, that is, wire feeders, motion systems, arc oscillation, among others.

Manual and mechanized welding

In manual welding, the metal is drip deposited, being added by one hand while the other controls the weld pool. In mechanized welding, the wire spool is placed in an automatic feeder with constant speed. The automatic system is used when the welding current exceeds 100 A; it can also be applied when the wire is preheated by the Joule effect, due to the passage of an electric current through it, before reaching the weld pool.

Consumable types and functions

Consumables used in plasma arc welding are: filler metal, ionization gas (plasma) and shielding gas. The tungsten electrode is not considered consumable but it also wears out over time.
  • The filler metal has the function of introducing filling material and facilitating the union.
  • Plasma has the function of providing a means for the transfer of electrons from the electrode to the workpiece (or vice versa)
  • The shielding gas has the function of shielding the molten pool from contamination by atmospheric air.

Joint preparation and cleaning

The preparation and cleaning of joints for Plasma welding requires all the care required for TIG welding, with special attention to:
  • The cleaning of the chamfer and edges must be to the shiny metal, in a range of 10 mm, on the inner and outer sides.
  • When deposition of the weld root, protection must be used, by means of inert gas, on the other side of the part. This gas injected into the root of the joint is called Purge. For carbon steels, protection is not required.
In keyhole plasma welding, joint preparation is decisive for the welding result. Butt joints can be adjusted to perform welds without filler metal. With imprecise adjustments, we work with addition wire; in this case, the preparation of the chamfers can provide for a greater height of the nose, in order to reduce the volume of filler metal.

Induced discontinuities

The welding inspector should note that, due to similarities with the TIG process, the PAW process can generate the same types of discontinuities.
As with TIG, the PAW process does not generate slag.

Safety considerations

The arc shape between the tungsten electrode and the weld pool is formed by an inert gas. As the filler metal is added directly into the weld pool, the metal does not pass through the arc so there is considerably less smoke emission.

In the case of welding aluminum or stainless steel, unacceptable levels of ozone can be generated. Because of this, means must be provided for it to be removed from the work environment. Care must also be taken regarding the electric and magnetic fields that are generated.


When you need to include a fact or piece of information in an assignment or essay you should also include where and how you found that piece of information (What Is Plasma Welding).

That gives credibility to your paper and it is sometimes required in higher education.

To make your life (and citation) easier just copy and paste the information below into your assignment or essay:

Luz, Gelson. What Is Plasma Welding?. Materials Blog. Gelsonluz.com. dd mmmm. yyyy. URL.

Now replace dd, mmmm and yyyy with the day, month, and year you browsed this page. Also replace URL for the actual url of this page. This citation format is based on MLA.


Didn’t find what you were looking for?


Materials: What is plasma welding? 👨‍🏭
What is plasma welding? 👨‍🏭
Loaded All Posts Not found any posts VIEW ALL Readmore Reply Cancel reply Delete By Home PAGES POSTS View All RECOMMENDED FOR YOU LABEL ARCHIVE SEARCH ALL POSTS Not found any post match with your request Back Home Sunday Monday Tuesday Wednesday Thursday Friday Saturday Sun Mon Tue Wed Thu Fri Sat January February March April May June July August September October November December Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec just now 1 minute ago $$1$$ minutes ago 1 hour ago $$1$$ hours ago Yesterday $$1$$ days ago $$1$$ weeks ago more than 5 weeks ago Followers Follow THIS PREMIUM CONTENT IS LOCKED STEP 1: Share to a social network STEP 2: Click the link on your social network Copy All Code Select All Code All codes were copied to your clipboard Can not copy the codes / texts, please press [CTRL]+[C] (or CMD+C with Mac) to copy Table of Content