09-05-2012, 03:27 PM
Friction Stir Welding
Friction_Stir_Welding AA.pptx (Size: 559.26 KB / Downloads: 65)
Introduction
Friction Stir Welding (FSW) is a solid-state joining process
FSW was developed by “The Welding Institute” in 1991
FSW is different from other conventional welding techniques
Principle of operation
A constantly rotating cylindrical-shouldered tool with a profiled nib is traversely fed at a constant rate into the joint between two clamped pieces of material.
Friction heat, heat generated by the mechanical mixing process and the adiabatic heat within the material, cause the stirred materials to soften without melting.
Heat Generation
A fraction of plastic deformation energy is stored in the form of increased defect densities
Deformation increases the dislocation density, the amount of grain surface and grain edge per unit volume and by cutting precipitates may force them to dissolve
local interfacial heat generation due to friction is the product of frictional force and the sliding velocity
Interfacial deformation heat is the product of shear stress and the velocity of the workpiece material which sticks to the tool as it moves
Heat Transfer
During tool–pin, insertion and extraction heat generation occurs at a constant rate
the weld profile and properties remain roughly constant during the welding phase.
The temperature and velocity fields in pseudo-steady state are commonly obtained by solving the continuity, momentum and energy equations for incompressible single–phase flow assuming steady state. Of the heat generated at the shoulder-workpiece interface, some of it is transported into the tool material while the rest enters the work–piece.