Friction hydro pillar processing (FHPP) is a friction welding technique which can be used for joining and repairing thick-section ferrous and non-ferrous plate materials.
FHPP is a solid phase technique and involves rotating a consumable rod co-axially in a drilled hole whilst under an applied load to generate frictional heat and a continuously plasticised layer (see illustration).
During FHPP, the consumable rod is fully plasticised across the bore of the hole and through the thickness of the workpiece. The plasticised material develops faster than the feed-rate of the consumable rod, which means that the frictional rubbing surface rises along the consumable to form a dynamically recrystallised deposit material.
The plasticised material at the rotational interface is maintained in a sufficiently viscous condition for hydrostatic forces to be transmitted, both axially and radially, to the bore of a parallel sided hole enabling a metallurgical bond to be achieved.
Since this material is being forced hydrostatically into the surrounding bore, the diameter of the deposit material is nominally greater than the feedstock material.
For materials which are less viscous and have a lesser tendency to extrude, tapered holes and consumables can be used. Friction taper plug welding (FTPW) allow a reactive force as well as hydrodynamic force to be exploited when making the joint and can also be used to fill through holes.
Also see: Friction Taper Plug Welding (FTPW)
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