Friction Welding | Advantages ,Disadvantages and Applications
Friction Welding (FRW) is a solid state welding process which produces welds due to the compressive force contact of work pieces which are either rotating or moving relative to one another. Heat is produced due to the friction which displaces material plastically from the faying surfaces. The basic steps explaining the friction welding process are shown in Fig.4.4.1. In friction welding the heat required to produce the joint is generated by friction heating at the interface. The components to be joined are first prepared to have smooth, square cut surfaces. One piece is held stationary while the other is mounted in a motor driven chuck or collet and rotated against it at high speed. A low contact pressure may be applied initially to permit cleaning of the surfaces by a burnishing action. This pressure is then increased and contacting friction quickly generates enough heat to raise the abutting surfaces to the welding temperature.
As soon as this temperature is reached, rotation is stopped and the pressure is maintained or increased to complete the weld. The softened material is squeezed out to form a flash. A forged structure is formed in the joint. If desired, the flash can be removed by subsequent machining action. Friction welding has been used to join steel bars upto 100 mms in diameter and tubes with outer diameter up to 100 mm.
Inertia welding is a modified form of friction welding, where the moving piece is attached to a rotating flywheel. The flywheel is brought to a specified rotational speed and is then separated from the driving motor. The rotating assembly is then pressed against the stationary member and the kinetic energy of the flywheel is converted in to frictional heat. The weld is formed, when the flywheel stop its motion and the pieces remain pressed together. Since the conditions of the inertia welding are easily duplicated, welds of consistent quality can be produce and the process can be easily automated. The heat affected zones are usually narrow, since the time period is very short for heating and cooling. The radial and orbital FRW are shown in figure.
Advantages of Friction Welding
1. No filler metal, flux or shielded gases are needed
2. It is an environment-friendly process with generation of smoke, fumes or gases.
3. No material is melted so the process is in solid state with narrow HAZ
4. Oxides can be removed after the welding process.
5. The process is very efficient and comparatively very rapid welds are made.
6. The weld is strength is stronger than the weaker of the two materials being joined
Disadvantages of Friction Welding
1. The process is restricted to joining round bars or tubes of same diameter
2. Dry bearing and non-forgeable materials cannot be welded. (i.e. one of the material must be ductile)
3. Preparation and alignment of the work piece may be critical for developing uniform rubbing and heating
4. Equipment and tooling cost are high
5. Free machining alloys are difficult to weld.
Application of Friction welding :
- Tongs hold to critical aircraft engine components
- Automotive parts like engine valve and shock absorber
- Hydraulic piston rod and track roller in agricultural equipment.
- Friction welded assemblies are often used to replace expensive casting and forgings
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