1. Small pass plasma arc welding
Small pass welding is also known as perforation, keyhole or penetration welding. Using the characteristics of high energy density of plasma arc and strong plasma current force, the workpiece is completely melted through and a small hole is generated through the workpiece. The metal being melted interacts with arc suction, liquid metal gravity and surface tension! Use it for balance. As the torch moves forward, the holes lock behind the arc, creating a fully penetrated weld.

The perforation effect can only be formed under the condition of sufficient energy density. Plate thickness increases: The required energy density also increases. Because the energy density of plasma arc is limited to some extent, the small-pass plasma arc welding can only be carried out in the limited plate thickness.

2. Penetration plasma arc welding
When the ion gas flow rate is small and the arc compression resistance is weak, the plasma arc can only melt the workpiece in the welding process without the pinhole effect. The principle of weld forming is similar to hydrogen tungsten arc welding, and this method is also called fusion type or corrosion plasma arc welding. It is mainly used for forming both sides of sheet and single side welding and multi-layer welding of thick plate.

3. Micro beam plasma arc welding
The fusion plasma arc welding below 15~30A is usually called micro-beam plasma arc welding. Due to the binding effect of nozzle and the simultaneous existence of arc current, the plasma arc with small current can be very stable, and has become an effective method for welding thin metal foils. In order to ensure the welding quality, the precision welding fixture should be used to ensure the assembly quality and prevent welding deformation. Special attention should be paid to the cleanliness of the workpiece surface. In order to facilitate observation, optical magnification observation system can be used.

Microbeam ion
Microbeam ions are commonly used for welding thin sheets (0.1mm thick), welding wires and mesh parts. The straight arc of the needle can minimize arc deviation and deformation. Although the equivalent TIG arc is more diffuse, newer transistorized (TIG) power supplies can produce very stable arcs at low current.

Medium current
This method can be selected for traditional TIG welding in the melting mode. It has the advantage of producing a deeper penetration (due to the higher temperature plasma flow) and allowing greater surface contamination including the coating (the electrode in the torch). The main disadvantage is that the welding torch is bulky, making manual welding more difficult. In mechanized welding, more attention should be paid to the maintenance of the welding torch to ensure stable performance.

microthyrid
Several advantages are available: deep penetration and fast welding speed. Compared with TIG arc, it can weld through sheets up to 10mm thick, but when using single-pass welding technology, the sheet thickness is usually limited to 6mm. The usual method is to use small holes with padding to ensure a smooth section of the bead (without teeth). Since the thickness is up to 15mm, the V-joint is prepared using a 6mm thick blunt edge. It is also possible to use the double pass welding technology, which automatically generates the first and second passes by adding a filler wire in the melting mode.
The welding parameters, plasma flow velocity and the amount of filler wire added (to fill the holes) must be precisely balanced to maintain the stability of the holes and the weld pool. This technique is only suitable for mechanized welding. Although this technique can be used for position welding by using pulsed current, it is usually used for high-speed flat welding of thicker sheet materials (over 3mm). When welding pipes, the overflow current and plasma flow velocity must be precisely controlled to ensure that the holes are closed.