Friction Stir Welding — Material Flow

In friction stir welding, a rotating pin tool plasticizes and mechanically stirs the metal along a joint line without ever melting it. This simulator visualizes the resulting material flow in the tool's own reference frame — a standard analytical simplification — as a steady velocity field combining solid-body rotation inside the pin radius, a decaying vortex in the surrounding stirred zone, a small outward extrusion term that spirals material into onion-ring bands, and the background traverse flow. Adjust spindle speed, traverse speed and pin radius to see the asymmetric advancing-side / retreating-side flow pattern reshape in real time, tracked live against the dimensionless advance ratio λ = ωR/v that governs how thoroughly the weld gets stirred.