Improving Machining Accuracy Using Smart Materials

Both economical and ecological factors might encourage conventional machines to continue in service by healing tool vibration problems. Higher productivity in automated manufacturing system brought to the attention the importance of machine tool error elimination. Various factors might affect the machining process (Merritt, 1965), some of them are non-measurable, and others might change in real-time. However, the wider use and availability of suitable and economical microcontrollers encouraged the use of intelligent control scheme to overcome such time dependent problem. Large magnitude of excitation forces with a tiny relative motion between cutting tool and working piece promote the use of smart material actuators that interfaced with microcontrollers to counteract such motion errors (Dold, 1996). Rigid fixture is a requirement to minimize displacements of cutting tools from its nominal position during machining. However, the reconfigurable manufacturing era encourage the use of small fixtures with lower mass (Gopalakrishnan, et al., 2002) and (Moo n& Kota, 2002). Previous dynamic modeling of a smart toolpost (Frankpitt, 1995) is based on linear piezo-ceramic actuator. The system is either modeled as lumped single rigid mass incorporating tool carrier (holder), tool bit, and piezo-actuator. Or by using an effective mass, stiffness, and, damping coefficients for the most dominant mode of vibration. The fundamentals of this model are incorporated to design an adaptive controller using the measured current, and, voltage applied to the actuator as a control signals. Based on identical principles (Eshete, 1996) and (Zhang et al., 1995) a mathematical model is derived for smart tool post using PMN ceramic material. A control system, and real time microprocessor implementation was examined in (Dold, 1996]. Sensitivity analysis for the toolpost design modifications and interfacing parameters on tool dynamic response require further elaboration. No conclusions are drawn related to better design and selection of actuator, tool holder and tool bit stiffness ratios. In