Rotational friction welding

Tab e 8.2 Rotational friction welding parameters for high-density PE pipes ... 

Inertia (friction) welding in the solid state, which is useful for joining dissimilar metals, i.e., aluminum to steel and stainless steel. At least one of the pieces to be welded must be circular and capable of being rotated at high velocities before being brought into contact with pressure to the second member. 

Friction welding is the most common solid-state process. One type, direct-drive friction welding, is accomplished by spinning one piece rapidly against a second, stationary piece to produce frictional heating. When the metal is at a forging temperature below the solidus, rotation is stopped and axial force is applied. Heated metal, together with oxide and surface contamination, is squeezed out of the interface between the two pieces in the form of a metal flash, which can be trimmed to form a smooth surface. 

In contrast to traditional friction welding, which is a welding process limited to small axisymmetric parts that can be rotated and pushed against each other to form a joint (Ref... 

Rotary Friction Welding Rotary friction welding (RFW) is the most popular method, where one workpiece is rotated as the two workpieces are brought together under friction pressure. It is widely used for the welding of tubes (Fig. 6). 

Pressure welding - where pressure only is applied, e.g. to a rotating part where the heat is developed through friction, as in friction welding. 

Pipe diameter (mm) Difference between outside and inside diameter of pipe (mm) Quality coefficient of friction welding Rotational speed (rpm) Friction time (s) Time of application of pressure (s) Total time (s)... 

Spin welding similar to Friction Welding (FRW), where the two parts to be joined, one stationary and one rotating at speed, have their joint surfaces brought into contact. Axial pressure and frictional heat at the interface create a solid state weld on discontinuation of rotation and on cooling (see 7.9). 

Spin Welding. Spin welding is an efficient technique for joining circular surfaces of similar materials. The matching surfaces are rotated at high speed relative to each other and then brought into contact. Frictional heat melts the interface and, when motion is stopped, the weld is allowed to soHdify under pressure. 

Retractable Pins. The retractable pin tool (RPT) consisted of an actuated pin within a rotating shoulder (Ref 94, 95) to allow pin length adjustment during FSW (Fig. 2.18). The normal operational mode for these tools was to retract the pin at a prescribed rate as the tool traversed forward. This allowed the closure of the exit hole in circumferential friction stir welds. 

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