Effect of tool diameter on formability in friction stir incremental forming was investigated. Formabilities were compared by forming pure titanium sheets which dimension is 100 mm x 100 mm x 0.3 mm. Tool diameters were 4, 5, 6 and 8 mm. From the experimental results, it was confirmed that as the diameter of forming tool became smaller, the formability became higher and the range of formable tool rotation rate was wider.
