Chatter, process damping, and chip segmentation in turning: A signal processing approach

An increasing number of aerospace components are manufactured from titanium and nickel alloys that are difficult to machine due to their thermal and mechanical properties. This limits the metal removal rates that can be achieved from the production process. However, under these machining conditions the phenomenon of process damping can be exploited to help avoid self-excited vibrations known as regenerative chatter. This means that greater widths of cut can be taken so as to increase the metal removal rate, and hence offset the cutting speed restrictions that are imposed by the thermo-mechanical properties of the material. However, there is little or no consensus as to the underlying mechanisms that cause process damping. The present study investigates two process damping mechanisms that have previously been proposed in the machining literature: the tool flank/workpiece interference effect, and the short regenerative effect. A signal processing procedure is employed to identify flank/workpiece interference from experimental data. Meanwhile, the short regenerative model is solved using a new frequency domain approach that yields additional insight into its stabilising effect. However, analysis and signal processing of the experimentally obtained data reveals that neither of these models can fully explain the increases in stability that are observed in practice. Meanwhile, chip segmentation effects were observed in a number of measurements, and it is suggested that segmentation could play an important role in the process-damped chatter stability of these materials

Determination of the steady state response of viscoelastically supported rectangular specially orthotropic plates with varying supported area

The influence of the amount of the supported area on the free and forced vibration properties of anisotropic plate is presented. Using the energy based finite difference method, the problem is modelled by a kind of finite difference element. Due to the significiance of the fundamental frequency of the plate, its variation was investigated with respect to the amount of the supported area on the plate, mechanical properties of plate material and translational spring coefficient of supports. The steady state response of viscoelastically supported plates was also investigated numerically for various damping coefficients and amounts of supported areas. Numerical results are obtained to investigate the effect of the ratio of the plate system. In the numerical examples, the natural frequency parameters and steady state responses to a sinusoidally varying force are assessed for the fundamental mode. Results showing effect of supported area ratios of plate indicate that variation of ratio of supported area of plate system is very significiant. Convergence studies are made. Many new results have been presented. Considered problems are solved within the frame work of Kirchhoff-Love hypothesis

Dynamics of Entanglement and Bell-nonlocality for Two Stochastic Qubits with Dipole-Dipole Interaction

We have studied the analytical dynamics of Bell nonlocality as measured by CHSH inequality and entanglement as measured by concurrence for two noisy qubits that have dipole-dipole interaction. The nonlocal entanglement created by the dipole-dipole interaction is found to be protected from sudden death for certain initial states

An experimental investigation of chatter effects on tool life

Tool wear is one of the most important considerations in machining operations as it affects surface quality and integrity, productivity and cost. The most commonly used model for tool life analysis is the one proposed by F.W. Taylor about a century ago. Although the extended form of this equation includes the effects of important cutting conditions on tool wear, tool life studies are mostly performed under stable cutting conditions where the effect of chatter vibrations are not considered. This paper presents an empirical attempt to understand tool life under vibratory cutting conditions. Tool wear data are collected in turning and milling on different work materials under stable and chatter conditions. The effects of cutting conditions as well as severity of chatter on tool life are analyzed. The results indicate significant reduction in tool life due to chatter as expected. They also show that the severity of chatter, and thus the vibration amplitude, strongly reduces the life of cutting tools. These results can be useful in evaluating the real cost of chatter by including the reduced tool life. They can also be useful in justifying the cost of chatter suppression and more rigid machining systems

Short communicationi: Shelled acorn seed (Quercus cerris) as a diet ingredient onthe performance of growing Japanese Quail

This study was carried out to investigate the effects of dietary inclusion of shelled acorn seed (Quercus cerris) on the growth performance and carcass yield of Japanese quail (Coturnix coturnix japonica). Four hundred four-day old quail chicks were used in this study. Experimental diets contained 0, 5, 10, 15 or 20% shelled acorn seed. The experiment lasted 38 days. There were no differences between treatments in body weight, body weight gain, feed intake and feed conversion ratio. Furthermore, the mortality rate and carcass yield were not affected by the inclusion in the diet of different levels of shelled acorn seed. The inclusion of shelled acorn seed to the quail diets did not cause any harmful effect on the health of the birds. These results suggested that up to 20% shelled acorn seed could be included as an energy source in quail diets. Keywords: Acorn seed, Coturnix coturnix japonica, growth performanceSouth African Journal of Animal Science Vol. 38 (1) 2008: pp. 38-4