Dynamics and stability predictions of variable helix milling

Abstract

In milling, it is important to research the stability lobes charts which determine stable regions where no chatter occurs. This paper presents the nonlinear model of milling considering the variable helix angle. Base on this model, an improved semi-discretization method is used to predict stability. Due to the delay between each flute varies along the axial depth of the tool in milling, the cutting tool is discrete into some axial layers to simplify calculate. The effects of variable helix angle and uniform helix angle on the corresponding stability charts are explored, it is revealed that many unstable islands arise in the low radial immersion ratio. However, as the radial immersion rates increase, variable helix angle has a little effect on stability. This fully shows that the helix angle plays an important impact for stability. Meantime this also confirms our proposed method can accurately capture unstable phenomenon at low radial immersion milling operations.