Dynamical characteristic validation of motorized CFRP spindle unit based on receptance coupling

Abstract

Carbon fiber reinforced plastic (CFRP) is used in machine tool components to provide high specific stiffness with high damping properties and low thermal expansion; further, it is combined with metals in specific ratios to enable the use of existing equipment and machine design. The development of CFRP spindle shafts has design flexibility in the stacking sequence. The improvement and analysis of spindle unit dynamics are essential for achieving high productivity in machining, and prediction methods for dynamic stiffness with lower computational costs are required to estimate and optimize the machine performance of the design proposals. Therefore, parameter identification for the equivalent physical properties of composite materials with CFRP and steel was proposed in this paper to use general solutions for a one-dimensional Timoshenko beam model. Four different analytical models of the CFRP spindle shaft following the actual development phase were designed via generalized receptance coupling to multi points in order to observe the model shapes. The frequency response functions and mode shapes of the spindle shaft models were compared with those of finite element methods and impact tests. The spindle shaft model reflecting the applicable location of CFRP in the rotational axis demonstrates a sufficient estimation accuracy for natural frequencies and mode shapes. The spindle shaft model reflecting the stacking sequence demonstrates robustness against the parameterization errors of the CFRP. A motorized CFRP spindle unit was modeled by combining a spindle shaft model and bearing models; the bearing dynamics were experimentally studied under heat radiation after stopping the spindle rotation. Moreover, a steel spindle shaft model and several types of CFRP layout with the same dimensions were compared on the spindle unit model; the CFRP spindle unit yielded a greater dynamic stiffness. The layout of the CFRP application and requirements on manufacturing are discussed for the further improvement of the dynamic stiffness.