In end milling process, undeformed chip thickness and cutting forces vary periodically with phase change of the tool. Recently, a model has been proposed to simulate the shear and friction characteristics of an up-end milling process in terms of the equivalent oblique cutting to this. In the current study, a down-end milling process has been replaced with the equivalent oblique cutting process. And shear and tool-chip friction characteristics variation of SM45C steel has been studied using the end-mills of different helix angles. The specific shear and friction energy consumed with helix angle of $50^{circ}$ is somewhat larger than those of$30^{circ}$ and $40^{circ}$. The specific shear energy consumed is about 76-77% of the specific cutting energy regardless the helix angles.