On the use of an instrumented spindle to determine the effects of machine stiffness in grinding brittle materials

The objective of this work is to experimentally investigate the role of grinding machine stiffness and its effect on the relationship between the equivalent chip thickness and grinding force, surface finish, and workpiece form.; The experiments are carried out using an innovative instrumented air bearing spindle developed in this work to measure grinding forces while the machine stiffness is varied using an annular flexure. A complete software analysis package is written to collect and analyze the force data in real time. The force resolution of the instrumented spindle system is shown to outperform commercially available measurement devices by an order of magnitude. The stiffness of a unique annular flexure design is engineered using basic calculations, finite element analysis, and experimental verification with special attention paid to the simplicity of the manufacture and assembly of the components.; A large number of tests are performed to determine the effect of grinding machine stiffness on machining force, surface roughness, and form error. An increase in machine stiffness is clearly seen to increase the static and the low frequency grinding forces, but the higher frequency force components are attenuated. Also, it is observed that the cutability (relation between the cutting force to the instantaneous depth of cut) is decreased as stiffness increases. For grinding cycles that include a spark-out, it is observed that surface roughness is independent of machine stiffness. Using the parallel-axis face grinding machine, it is found that form accuracy decreases slightly with increasing feed rate but no trend is found with respect to stiffness.; The instrumented grinding system addresses the need for high frequency force feedback during ductile regime machining of brittle materials. The static and dynamic stiffness of the structural loop of the grinding system meets or exceeds those of previous researchers and provides a general-purpose force measurement tool for fine grinding and is capable of resolving intra-revolution force components. The analysis of the force spectra in this dissertation shows that increasing machine tool stiffness does lead to higher forces for a given material removal rate. It is found in this work that the spectra afford efficient process optimization and can be used to determine the rubbing/grinding transition for brittle materials.