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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.

No description available.

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

Thesis (MScEng) -- Stellenbosch University, 2003. / ENGLISH ABSTRACT: High Speed Cutting (HSC), specifically milling is a significant contemporary development in machining. The Die and Mould industry is experiencing a difficult business climate. There is competitive pressure for shorter lead times and lower prices. Companies worldwide, are under financial pressure, to meet the challenges of a globalised business environment. The conventional position of milling and Electric Discharge Machining (EDM / Erosion) is discussed with the proposal to use HSC and EDM as complementary processes. Among new developments the progress in computer infrastructure is prominent. There is also a paradigm shift that should be made from experience based process planning to modern, up to date knowledge based process planning. High Speed Cutting is now a mature process capable of acceptable process security. The examples detailed include crankshaft-forging tooling, injection moulding tooling and powder sintering tooling. A process chain is proposed for the complementary HSC / EDM process with estimated illustrative time saving over the conventional EDM dominated process. HSC will be the first process removing the bulk of the material, finishing as far as possible and with EDM finally machining the features that will be difficult or impossible with HSC. To facilitate the use of the complementary processes a decision model to determine the crossover point between HSC and EDM is proposed. The decision model is firstly presented as a flow diagram to determine whether the task is a candidate for HSC only, EDM only, or the complementary HSC / EDM process. The key parameters e.g tool H d ratio are variables. This is in order that the flow diagram may be adapted to a specific machine tool infrastructure and expertise level in a company. The second part is a HSC machining time estimation model. The time is estimated per segment roughed, semi-finished, or finish machined. The model is in an empirical form with constants that can be adapted to the practices of a specific company. It is intended that the constants also be periodically revised to reflect the development in HSC expertise that will occur during the use HSC in the company. The model is practically evaluated with a case study, including the detail steps, not included in the model. Conceptual guidelines are given for software implementation. It is concluded that HSC and EDM are suitable complementary processes. It is a necessary prerequisite to use pallets to avoid multiple set-ups. Complementary HSC and EDM is especially appropriate for the gradual deployment and skill development for HSC. HSC and complementary HSC / EDM is considered the opportunity for companies to make a major breakthrough in lead time and operating expense if the necessary pallet/fixturing equipment, CAx infrastructure and human capability is available. / AFRIKAANSE OPSOMMING: Hoe Spoed Masjinering (HSC), spesifiek frees is ‘n betekenisvolle ontwikkeling in masjinering. Die Gereedskap en Gietvorm bedryf ervaar ‘n moelike besigheidsklimaat. Daar is kompeterende druk vir korter lewertye en laer pryse. Maatskappye wereldwyd is onder finansiele druk om in die geglobaliseerde besigheidsmilieu te presteer. Die posisie van frees en Elektriese Ontladingsmasjinering (EDM / Vonkerosie) word bespreek met die voorstel om HSC en EDM as komplementere prosesse te gebruik. Onder die nuwe ontwikkelings is daar prominente vooruitgang in rekenaarinfrastruktuur. Daar is ook ‘n paradigmaverskuiwing nodig van ondervinding gebaseerde na op datum kennis gebaseerde proses beplanning. HSC is nou ‘n ontwikkelde proses met voldoende prosessekerheid. Die voorbeelde sluit krukas smee gereedskap, inspuitgiet gereedskap, en poeier-sinter persgereedskap in. ‘n Prosesketting word voorgestel vir die komplementere HSC / EDM proses met ‘n beraamde illustratiewe tydbesparing oor die konvensionele EDM gedomineerde proses. HSC sal die eerste proses wees wat die meerderheid van die materiaal verwyder en oppervlaktes so ver as moontlik afwerk, met EDM wat die finale afwerking doen en ook die masjinering wat vir moeilik haalbaar of onmoontlik is vir HSC. Om die gebruik van die komplementere prosesse te fasiliteer, word ‘n beluitnemingsmodel vir die oorgangspunt tussen HSC en EDM voorgestel. Dit word eerstens as vloeidiagram gebruik om die taak te klassifiseer vir HSC alleen, EDM alleen of vir komplementere HSC en EDM. Die sleutelparameters, bv die beitel 116 verhouding, is veranderlikes. Dit is sodat die vloeidiagram aangepas kan word by ‘n spesifieke masjienvermoe en ‘n kundigheidsvlak in ‘n maatskappy. Die tweede deel is ‘n HSC masjineringstyd model. Die tyd word beraam per segment uitgerof, afgewerk, of finaal afgewerk. Die model is in empiriese vorm met konstantes wat kan aangepas word by die praktyke van ‘n firma. Dit is die bedoeling dat die konstantes periodiek aangepas word om die ontwikkeling te weerspieel wat in die maatskappy plaasvind. Die model word prakties evalueer met ‘n gevallestudie, insluitend die detailstappe, wat nie in die modelformulering ingesluit is nie. Konseptuele riglyne word gegee vir programmatuur implementering. Die gevolgtrekking word gemaak dat HSC en EDM geskikte komplementere prosesse is. Dit is ‘n voorvereiste om pallette te gebruik om veelvuldige opstellings te vermy. Komplementere HSC / EDM is veral toepaslik om HSC geleidelik in ‘n firma te ontplooi en kundigheid te bou. Die HSC / EDM kombinasie word ook die geleentheid geag vir firmas om ‘n deurbraak te maak in lewertyd en bedryfsuitgawes as die nodige pallettoerusting, CAx infrastruktuur en menslike vermoe beskikbaar is.