Optimisation of variable helix tool geometry for regenerative chatter mitigation

It is well known that regenerative chatter can result in excessive tool wear, poor surface finish, and hence limited productivity during metal machining. Various mitigation methods can be applied to suppress chatter; however, the current paper focuses on applying optimal variable helix tool geometry. A semi-discretisation method is combined with Differential Evolution to optimise variable helix end milling tools so as to avoid chatter by modifying the variable helix and variable pitch tool geometry. The semi-discretisation method is first validated experimentally. The numerical optimisation procedure is then used to optimise tool geometry for a machining problem involving a flexible workpiece. The analysis predicted total mitigation of chatter using the optimised variable helix milling tool at a low radial immersion. However, in practice a five fold increase in chatter stability was obtained, compared to the traditional milling tool.