During the process, both the energy density and temperatures are much higher, since the plasma state is obtained when a gas is heated to a temperature sufficient to secure its ionization, separating therefore the element into ions and electrons.
In plasma welding, the energy needed to obtain ionization is provided by the electric arc that is established between a tungsten electrode and the welted base metal. Three modes of performance can then be produced by varying the diameter of the hole and the flow rate of plasma gas.
Micro plasma: 0.1A – 15A
The micro plasma arc can be operated with very low welding currents. The columnar arch is stable, even when the length of the arch varies up to 20 mm. Micro plasma was traditionally used to weld thin sheets (up to 0.1 mm thick), wire and meshes. The needle-like rigid arch minimizes bow deflection and distortion. Although the equivalent TIG arc is more diffuse, new transistorized power sources (TIG) can produce a very stable arc at low current levels.
Average current: 15A – 200A
At higher currents, from 15 to 200 A, the characteristics of plasma arc process are similar to the TIG arc, but because the plasma is constricted, the arc is more rigid. Although the plasma gas flow can be increased to improve the penetration of the weld puddle, there is a risk of entrainment air and shield gas through an excessive turbulence in the gas monitor screen. When used in the fusion way, this is an alternative to the conventional TIG. The advantages are a deeper penetration (higher plasma gas flow) and a greater tolerance to surface contamination, including coatings (the electrode is inside the body of the torch). The main disadvantage lies in the volume of the torch, making manual welding more difficult. In mechanized welding, greater attention must be paid to maintaining the torch to ensure uniform performance.
Key Hole: more than 100A
By increasing the welding current and plasma gas flow, a very powerful plasma bundle is created that can achieve full penetration into a material, such as laser welding or bundle of electrons. During welding, the hole progressively cuts the metal, with the puddle welding out, which flows back to form the weld bead under surface tension forces. This process can be used to weld thicker material (up to 10 mm of stainless steel) in a single pass. It has several advantages that can be exploited: deep penetration and high welding speeds