Plasma Arc Welding | Transferred Type Plasma Arc Welding | Non-transferred Type Plasma Arc Welding

Plasma arc welding

Principle

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.

Working

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.

01 - PLASMA ARC WELDING - TYPES OF WELDING PROCESS

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

01 - TRANSFERABLE TYPE PLASMA WELDING - NON-TRANSFERABLE TYPE PLASMA WELDING

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

· T-Welds

· Grooves

· 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.

Applications

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.

Forging Process | Types of Forging

FORGING PROCESS

In this process the desired shape is obtained by the application of a compressive force over the metal. In hot forging process the metal is heated above the recrystallization temperature. This hot metal is then compressed to the desired shape using hammer or press tool.

There are three types of forging process.

· Open die forging process

· Closed die forging process

· Roll forging process

OPEN DIE FORGING

In this type of forging process the work piece is heated to a very high temperature and it is placed on a flat surface and hit using a hammer to obtain the desired shape. This type of forging is very simple and flexible. It is very much useful in producing rough components like chisel, bolts, and rectangular, circular, hexagonal shapes. In this the forging hit is given either by hand or by power.

CLOSED DIE FORGING

1. DROP FORGING

The impression dies used in this process is called as closed dies. The upper die is fitted on the ram and the lower die is fitted on the anvil. Both the dies have impression. Two rollers are held on the board supporting the ram. These rollers rotate in opposite direction to each other. This makes it to drive the board upwards and lifts the ram. By releasing the rollers the ram falls down producing the working stroke. For producing simple parts a single stroke is enough. large components are produced by number of steps.

01 - DROP FORGING - TYPES OF FORGING PROCESS

APPLICATIONS

It is generally used for making spanner, automobile parts, and machine parts.

2. PRESS FORGING

Press forging is done with the help of a press. The press may either be operated mechanically or hydraulically. It is a slow squeezing process rather than delivering heavy blows. The lower die is fitted with the anvil and the upper die is fitted with the ram. The ram is slowly a moved down and it slowly presses the metal. The finished component may be removed from the die with the help of ejectors in the die set. The speed of press forging varies from 34 to 40 strokes per minute.

01 - PRESS FORGING - TYPES OF FORGING

APPLICATION

Press forging is used for making components such as connecting rods, machining components, spanner, etc.

3. UPSET FORGING

01 - UPSET FORGING - TYPES OF FORGING PROCESS

This process is generally used to make head of bolts, rivets or pins. The shape of the head may be square, hexagonal or hemispherical. The machine holds a die set which consists of a fixed die and movable punch. The heated metal bar is held in the die and the force is given to the punch. So the desired shape is obtained with the help of die cavity.

ROLL FORGING

The roll forging machine consists of two horizontal rolls. The heated metal bar is passed between the two rolls. Roll forging is performed in an impression-die.

01 - ROLL FORGING - TYPES OF FORGING

A bar of heated rod is passed between the rolls. As the rolls rotate the heated metal is squeezed between them. This method is used for reducing the cross sectional area and for producing taper ends.