The influence of steel reinforcements on static rigidity of epoxy granite spindle head for dynamic performance enhancement of machining center: Experiments and finite element simulation

Abstract

Machine tool structures are subjected to continuous distortions and unwanted vibrations during machining. The structures should have excellent static and dynamic properties to minimize the adverse effects due to vibration. Cast iron is generally used as a structural material for machine tools owing to its higher structural rigidity and moderate damping properties. The lack of desired dynamic properties results in poor surface finish of the machined components. Epoxy granite is a resin mineral-based composite found to provide superior damping ability but it has lesser material stiffness. Steel reinforcements are more appropriate to enhance the static rigidity of epoxy granite structures. The cast iron spindle head of the vertical machining center is considered for the present study. Static structural analysis has been performed by finite element analysis and the results are considered as a benchmark for the design of epoxy granite spindle head. Multiple design configurations of steel reinforcements are evolved through topology optimization to achieve improved stiffness with a higher damping ratio. A model which exhibited higher stiffness with minimum steel has been proposed for fabrication. A 1:2 scaled model of the proposed configuration has been fabricated using epoxy granite. Experimental modal analysis and numerical static analyses have been carried out and the results are compared to those of cast iron spindle head. A significant reduction in mass and deformation of the epoxy granite spindle head by 22% and 57%, respectively, was observed compared to that of cast iron spindle head.