8 December 2017

Friction welding

It is a solid-state welding process that generates heat through mechanical friction between workpieces in relative motion to one another with the use of lateral force and fuses the materials. 
Friction welding is not a fusion welding process because no melting occurs. 

Working principle :

In this process of welding, the heat required for welding is obtained by the friction between the ends of the two parts to be joined. One of the parts to be joined is rotated at a high speed around 3000 RPM and the other part is axially aligned with the second one and pressed tightly against it.

Also, the friction between the two parts raises the temperature of both the ends. After that, the rotation of the part is stopped abruptly and the pressure on the fixed part is increased so that the joining takes place. 

Friction welding

Machine set up :

The machine for friction welding is similar to a centre lathe. Through a centre lathe could be used for smaller sized jobs, the bigger ones required a special welding machine because in a lathe machine power available would not be sufficient. The power requirements of friction welding may be between 25 kVA to 175 kVA, which is far beyond that of the many general-purpose centre lathes. 

Major parameter :

The major parameters in friction welding are the rotational speed and the axial pressure applied. The axial pressure applied depends on the strength and hardness of the metals being joined. 

The pressure may range from 40 Mpa for low carbon steels to as high as 450 Mpa for alloy steels.

The rotational speed may also change the requirement of the pressure. It may be of the order of 1500 to 3000 RPM.  

The other variable that needs to be closely controlled is the time of contact between the two parts. The total welding time that is taken in the friction welding is between 2 to 30 seconds. 

Advantages of friction welding :
  • The major advantage of friction welding is the ease with which the joining can take place. 
  • Edge cleaning is not a problem since the oxides and contaminants present would easily be removed during the initial rubbing. 
  • The heat generated is small and well below the melting temperature, there will be no distortion and warping. 
  • The quality of the weld achieved is very high and it is economical in operation. 
  • No skilled operator required since it completely automatic in operation. 
Because of the above advantages, the quality of weld obtained is very high so that the friction welding has been widely accepted in the aerospace industry as well as the automobile industry for the welding of critical parts. 

Disadvantages of friction welding :
  • This welding process mostly used only for round bars of some cross-section.
  • Non-forgeable materiel can not be weld.
  • Preparation of workpiece is more critical.
  • High machine setup cost. 
  • Joint design is limited. 
  • It can only be used for smaller parts of machines, big parts are not compatible with it.