Influence of composite spindle ram on machine tool dynamic stiffness

Demands for improving machine tool productivity and accuracy can be addressed using alternative material structures with the potential to reduce the mass of moving bodies and decrease machine tool dynamic compliance. A useful option is to apply composite materials because they offer high damping and low density in comparison with steel or cast iron. The key question is how the stiffness and damping of a single composite or hybrid metal + composite component influences the behaviour of the machine tool. In this paper, simulation models for the prediction of machine tool dynamic compliance were prepared for a detailed analysis of a use case study using a hybrid and ductile iron spindle ram for a portal milling centre. A simplified model for the damping matrix formulation was assembled and the influence of the spindle ram damping on the dynamic compliance was tested along with stiffness and mass change, leading to conclusions about the effect of a single component redesign. The minor influence of the material damping of the hybrid structure is noted, and factors influencing the final dynamic compliance are discussed in detail.