Flow stress is a vital input data for successful simulation of a machining process. However the flow stress data obtained from experiments do not represent the practical machining conditions which induce errors in the simulated output. In this research work the flow stress of Ti6Al4V titanium alloy is improved through a new integrated Taguchi – Finite element optimisation technique. The finite element (FE) outputs for cutting force, feed force and chip thickness ratio are compared with the results from the orthogonal machining process and an optimum set of material parameters of the Johnson – Cook (JC) flow stress equation is identified. The optimised flow stress is found to improve the simulated cutting forces by 3-16 %, feed forces by 2-25 %, chip thickness ratio by 0-19 % over flow stress computed from conventional JC model parameters. The yield strength parameter of the JC model impacts the simulation results the most and the JC material constitutive law is found to be robust in flow stress characterisation with the optimized parameters. (Received in March 2011, accepted in September 2011. This paper was with the authors 1 month for 1 revision.)