A better understanding of friction modeling is really important for producing more realistic finite element models of machining processes. This paper presents a methodology to determine the friction at the tool-chip interface. By matching the measured values of the cutting forces with the predicted results from finite element simulations (FEM), a revised friction model on the tool-chip interface is developed. Reasonable distribution of the stress, strain and strain-rate, as well as the temperature fields at the tool-chip interface could be achieved by using this approach. An attempt is made by FEM to obtain a full understanding of relationships between the complex physical behavior and friction at the tool-chip interface. It is found that the sticking-sliding separated area is located at the points with the greatest temperature. And the corresponding relationship between cutting parameters and sticking-sliding friction separated area is found.