Tuesday, 22 December 2015

Friction Welding

Friction Welding (FRW) is a solid state welding process which produces welds due to the compressive force contact of workpieces 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.
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 upto 100 mm.

Advantages of Friction Welding

1. No filler material, flux or shielding gases are needed.
2. It is an environment-friendly process without generation of smoke, fumes or gases.
3. No material is melted so the process is in solid state with narrow heat affected zone (HAZ).
4. Oxides can be removed after the welding process.
5. In most cases, the weld strength is stronger than the weaker of the two materials being joined. 6. The process can be easily automated for mass production.
7. The process is very efficient and comparatively very rapid welds are made.
8. Plant requirements are minimal and wide variety of metals and combinations can be welded.

Limitations of Friction Welding
1. Process is restricted to Object that can be rotated about its axis
2.one of the component must be ductile when hot, to permit deformations.
3. Preparation and alignment of the workpieces may be critical for developing uniform rubbing and heating
4. Tooling costs are high and free-machining alloys are difficult to weld

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