This paper presents a novel welding quality evaluation approach based on the analysis of IMR and process capability for friction stir welding. The method has been implemented in an experimental work developed using the rotation speed range was from 485 to 1 800 rpm with a travel speed travel speed range from 4 to 10 mm/min. This ranges applied with different material thicknesses from 2 to 4 mm. This research approach to DMAIC (“define – measure – analyze – improve – control”) analysis to attachment potency and technical commonplace demand. The analysis controlled the tensile strength, elongation and hardness of the Al 6061 friction stir welded joints. Friction stir welding process has three main variables: rotation speed, material thickness and travel speed. Different friction stir welded samples were produced by changing these three variables. The result was improving the values of the process capability index Cpk from (0.86, 0.37, 0.81) to (0.69, 0.57, 0.58) for the tensile strength, elongation and hardness respectively.