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Friction Welding (FRW)

] Produces a weld by simultaneously applying

compressive force and relative motion (usually rotation)between the faying surfaces. Heat is produced as thefaying surfaces rub together. However, the process is

considered solid-state because melting generally doesnot occur. The compressive force causes plastic flow(displacement), expelling material from the joint. The

expelled material is called flash. Filler metal, flux andshielding gas are not required.

] Figures 23.1, 23.4, 23.5, 23.6 and 23.7 illustrate variations ofthe process.

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Energy Input Methods

] Direct Drive Welding (conventional)- One workpiece is

restrained while the other is attached directly to a motordrive unit.

] Inertia Drive Welding (flywheel)- One workpiece is

restrained and the other is attached to a flywheel.

\ Note: Flywheels are devices used to store kinetic energy.

For instance, a small motor can be used to rotate arelatively large and heavy wheel. Once the wheel is at fullspeed, the energy stored within it can be used to performwork that the small motor is not capable of doing by itself.

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Types of Relative Motion

] Most friction welding is performed by holding one of the

two workpieces stationary while the other is rotatedabout an axis of symmetry with the faying surfacesperpendicular to that axis. (See figures 23.1 and 23.4.)

Other types of motion include:\ Radial - figure 23.5

\ Orbital - figure 23.6

\ Friction - figure 23.7A

\ Angular Reciprocating - figure 23.7B

\ Linear Reciprocating - figure 23.7C

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Process Characterization

]

2 Main Mechanisms (fig. 23.2 & 23.3):\ Friction Stage

\ Forging Stage

] Primary Process Variables:

\ Speed\ Pressure

\ Time

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Friction Welding Advantages

] No filler metal needed.

] Flux and shielding gas not required.] Environmentally clean (no arc, sparks, smoke or fumes).

] Surface cleanliness not as critical as some processes.

] Narrow heat-affected zone (HAZ)

] Suitable for most materials and many dissimilarcombinations.

] Less operator skill required.

] Good for mass production. (drill bits)

]

Rapid process.

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Friction Welding Limitations

] One workpiece must have an axis of symmetry that it

can be rotated about.

] Preparation and alignment are critical.

] High equipment and tooling costs.

] Some materials cannot be friction welded.

] Special machines required for parts longer than 3-foot.

]Process turns the grain direction 90 creating potentialfor preferential corrosion.

Source (all slides) - AWS Handbook, Volume 2, eighth edition.