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One of the major limitations on productivity in metal cutting is chatter. Chatter is a form of unstable self-excited vibration which causes poor surface finish, as well as cutter and machine tool damage. The investigation of chatter suppression in milling using continuously variable spindle speed is presented in this thesis. The fundamental mechanism in regenerative chatter is due to favorable phasing between the inner and outer modulations on the chip thickness. In this thesis, the spindle speed is sinusoidally varied to prevent the dynamic cutting process from locking on to a constant phase shift and causing unstable cutting, or chatter. Because of the nonlin-earities and complexities of the process, time domain simulation of the dynamic cutting process has been modelled. The influence of various parameters, such as axial depth of cut, process damping from flank interference, and amplitude and frequency of speed variation have been investigated using the simulation model. The trends predicted by simulation results have been experimentally verified using cutting tests on a milling machine. It has been concluded from simulation and milling tests that a variable spindle speed can partially increase the chatter limit, but can never totally prevent chatter. The variable spindle speed strategy is incorporated into a proposed in-process chatter detection and avoidance algorithm. The milling process is monitored using the sound pressure signal measured by a microphone. When the amplitude of the sound spectrum near the natural frequency exceeds a threshold value, chatter has been detected and the spindle speed is oscillated until stability is regained. The proposed algorithm is implemented on line and experimental results are presented. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

Thesis (Ph.D.)--McMaster University, 2003. / Advisor: M. Elbestawi. Includes bibliographical references ( leaves 221-243). Also available via World Wide Web.

Certain surface-active media can considerably influence the flow and fracture properties of the .solids they wet. The effects of various lubricating media on the sliding friction behaviour of diamond on soda-lime glass were studied in the present research. An experimental apparatus was constructed to slide a hemispherical diamond linearly and at constant speed across the surface of a Corning type 2947 soda-lime glass microslide and to measure the resultant friction force. Tests were conducted in a variety of liquid and gaseous media at sliding speeds ranging from 0.001 cm/sec to 0.4 cm/sec. As a base for comparison initial tests were conducted in a high vacuum — 8 at 4 x 10 ⁻⁸. The results showed that all the media enhanced material displacement from that observed in high vacuum. In addition, the friction force was observed to rise with displaced material. A simple theory was used to predict with reasonable agreement the results obtained in in vacuum and air only. The greatest increase in displaced material was observed in heptyl alcohol. Scanning electron micrographs of the friction tracks suggest that heptyl; alcohol softened the surface of the glass. This is in agreement with previous work. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

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Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1990. / Vita. Abstract. Includes bibliographical references (leaves 88-92). Also available via the Internet.

Current manufacturing research aims at increasing productivity by optimal selection of process parameters. This is accomplished by understanding the fundamental physics of individual manufacturing processes. In this thesis, peripheral milling of very flexible cantilevered plates is studied. The static and dynamic deflections of the plate under periodic milling forces are modelled. A new dynamic cutting force model is developed which considers five discrete zones of relative motion between the tool and the workpiece. The kinematics of both milling and vibratory motions are modelled, which is an original research contribution in this area. It is shown that the penetration of the tool into the workpiece during vibratory cutting has a strong influence on the damping and stiffness characteristics of the milling process. A structural model of a discontinuous cantilevered plate is determined using the finite element method. A reduced order structural model at the tool-workpiece contact zone is implemented for discrete time response analysis of the plate under cutting force excitations during milling. The closed loop dynamic behaviour of the system is modelled and taken into account in the analysis. Simulations of plate machining are compared with experimental results. A model of the surface finish generation mechanism is deduced from the analysis and experimental results. Applications of this research include peripheral milling of integral jet engine impellers, computer disk drives and other flexible mechanical components. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate