Plasma arc welding
Plasma is nothing but a high temperature ionized gas. It is generally a mixture of positively charged atoms and neutral charged atoms and free elements. When this high temperature plasma is passed through the orifice, the proportion of the ionized gas is increased and the plasma arc welding is formed.
When the high heat content plasma gas is forced through the torch orifice surrounding by negative tungsten electrode in the form of jet. The plasma cutting force imposes a swirl on the orifice gas flow. The arc is initiated in the beginning by supplying electrical energy between nozzle and tungsten electrode. This will release high energy and heat. This heat is normally in between 10,000C t 30,000C.
This high amount of heat energy is used to weld the metal. There are two types plasma Arc welding used practically..
1. Transferred type
In transferred type, the tungsten electrode is connected to the negative terminal, work piece is connected to the positive terminal. An electric arc is maintained between the electrode and the work piece heats a co-axial flowing gas and maintain it in a plasma state. It is difficult to initiate the arc first between the work piece and the electrode. For that, the pilot arc is struck between the nozzle and the electrode.
2. Non-transferred type
In this type, power is directly connected with the electrode and the torch of nozzle. The electrode carries the same current. Thus, ionizing a high velocity as that is strewing towards the work piece. The main advantage of this type is that the spot moves inside the wall and heat the incoming gas and outer layer remains cool. This type plasma has low thermal efficiency
The base metals welded by plasma arc welding are
· Stainless steels
· Titanium alloys
· Carbon and low alloy steels
· Copper alloys
· Aluminium alloys
The types of joint which are made by plasma Arc welding are
· Filler welds
· Square groove
The main advantage of plasma welding is that the control and quality finished in the part being welded. The torch design allows for improved control of the arc, along with a higher tolerance for in torch standoff distance. Welds are usually cleaner and smoother when using the PAW process. Smaller heat-affected zones result in welds that are very strong and less noticeable, which is important for some parts.
A major limitation in executing a plasma welding process is the relatively high startup costs. Plasma welding equipment tends to be expensive. Because it is a more focused welding process, the training and expertise mandatory is also more intense.
It is in Aerospace applications.
It is used for melting high melting point metals
It is used for welding titanium plates.
It is used in welding nickel alloys.
It is used for tube mill applications.