Haptic devices and haptic rendering is an important topic in the burgeoning field of virtual reality applications. In this thesis, I describe the design and implementation of a cutting force model integrating a haptic device, the PHANToM, with a high &ndash / powered computer. My goal was to build a six degree &ndash / of &ndash / freedom force model to allow user to interact with three &ndash / dimensional deformable objects. Methods for haptic rendering including graphical rendering, collision detection and force feedback are illustrated, implementation of haptic rendering system is introduced, and application is evaluated to explore the effectiveness of the system.

Thesis (MEng)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Efficient face milling of titanium alloys provides a global challenge. Difficult-to-cut super alloys such as Ti-6Al-4V is considered the “workhorse” material for aerospace components. During the machining of aerospace components, 80% – 90% of the material is removed. This requirement drives the innovation for machines and tooling to become more efficient, while driving down costs. In South Africa, this requirement is no different. Due to the historic practice of exporting valuable minerals such as Ilmenite, leucoxene and rutile, South Africa does not enjoy many of financial benefits of producing value added titanium alloy products. The Titanium Centre of Competence (TiCoC) is aimed at creating a South African titanium manufacturing industry by the year 2020. More specifically, the roughing of Ti-6Al-4V aerospace components has been identified as an area for improvement. The thermal conductivity of Ti-6Al-4V is significantly lower than that of other “workhorse” metals such as steel or aluminium. Therefore, heat rapidly builds up in the tool tip during high speed machining resulting in shortened tool life and increased machining costs. Hence the ongoing developments in the field of cooling methods for high speed machining. The latest development in high pressure cooling (HPC) is split tools that deliver coolant into the cutting interface via flat nozzles in the rake face of the insert. Although it has been released recently and limited to a single supplier, this cooling method is commercially available, yet little is known about its performance or application conditions. The operational characteristics of split tools are studied by answering set research questions. A dynamometer was used to measure the tangential cutting forces during 11 cutting experiments that follow a three-factor factorial design at two levels and with three centre points. A second-order model for predicting the tangential cutting force during face milling of Ti-6Al-4V with split tools was fit to the data at 95% confidence level. A predictive cutting force model was developed in terms of the cutting parameters: (1) Axial depth of cut (ADOC), (2) feed per tooth and, (3) cutting speed. The effect of cutting parameters on cutting force including their interactions are investigated. Data for chip evacuation, surface finish and tool wear are examined and discussed. Practical work was done at a selected industry partner to determine: (1) impact of an analytical approach to perform process development for aerospace component roughing, (2) determine the feasibility of implementing split tools to an existing process. A substantial time saving in the roughing time of the selected aerospace component was achieved through analytical improvement methods. Furthermore it was found that the split tools were not a suitable replacement for current tooling. It was established that certain critical operational requirements of the split tools are not met by the existing milling machine at the industry partner. / AFRIKAANSE OPSOMMING: Doeltreffende masjinering van titaan allooie bied `n wêreldwye uitdaging. Moeilik-om-te-sny super allooie soos Ti-6Al-4V word as die “werksesel” materiaal vir lugvaart komponente beskou. Gedurende die masjinering van lugvaart komponente word 80% - 90% van die materiaal verwyder. Dit is hiérdie behoefte wat die innovering van masjien -en snygereedskap dryf om dit meer doeltreffend en finansieël vatbaar te maak. Die Suid Arikaanse behoefte vir doeltreffende snygereedskap vir Ti-6Al-4V masjinering stem ooreen met hierdie internationale behoefte. Die geskiedkundige Suid Afrikaanse praktyk om onverwerkte, waardevolle minerale soos Ilmeniet, rutiel en leucoxene uit te voer, kniehalter die land se kans om winste uit verwerkte titaan allooi produkte te geniet. Die “Titanium Centre of Competence” (TiCoC) se mikpunt is om `n Suid Afrikaanse titaanproduk vervaardigingsmark op die been te bring teen 2020. Stellenbosch Universiteit se funksie, binne hierdie strategiese raamwerk, fokus op hoë spoed masjinering van Ti-6Al-4V lugvaart komponente. Die hitte geleidingsvermoë van Ti-6Al-4V is noemenswaardig laer as die van ander “werksesel” materiale soos byvoorbeeld staal of alumium. Om hierdie rede word hitte in die freesbeitelpunt gedurende hoë spoed masjinering opgeberg. Dit verkort gereedskap leeftyd en verhoog masjinerings kostes. Daarvandaan deurlopende ontwikkelinge in verkoelingsmetodes vir hoë spoed masjinering. Die mees onlangse ontwikkeling in hoë druk verkoeling is “split tools” wat koelmiddel na die snyoppervlak deur middel van langwerpige gleufies in die hark gesig van die beitelpunt lewer. Hierdie tegnologie is op die mark beskikbaar, maar slegs deur `n enkele verskaffer. Daar is ook geen akademiese publikasies wat oor Ti-6Al-4V masjinering met “split tools” handel nie. Die verrigtings vermoë en toepassings gebied vir die gereedskap is steeds onbekend. 'n Dinamometer is gebruik om die tangensiale snykragte tydens 11 sny eksperimente te meet. Die eksperiment ontwerp is faktoriaal van aard en bevat drie faktore en drie middelpunte oor twee vlakke. `n Kwadratiese model is geskik om die data op 95% vertroue vlak voor te stel en voorspellings mee te maak. Die voorspellingsmodel is ontwikkel in terme van: (1) Diepte van snit, (2) voertempo, en (3) Snyspoed. Die invloed van die drie parameters op die tangentiale snykrag, asook invloed met mekaar word ondersoek. Verdere data in verband met materiaal verwydering, oppervlak afwerking en beitel slytasie word ook bespreek. Praktiese werk is met behulp van `n bedryfsvennoot gedoen om vas te stel: (1) die impak van 'n analitiese benadering en ontwikkelings proses op die uitrof van lugvaart komponente, (2) en om die lewensvatbaarheid van implementering van “split tools“ aan 'n bestaande proses te bepaal. `n Noemenswaardige besparing is sodoende behaal. Dit is verder bevind dat “split tools” nie `n geskikte plaasvervanger vir die huidige snygereedskap is nie. Die rede daarvoor is gedeeltelik omdat die huidige freesmasjien by die bedryfsvennoot nie aan die kritiese operasionele vereistes van die gereedskap vervaardiger voldoen nie.

Turning is one of the most widely used processes in machining and is characterized by a cutting tool moving along the axis of a rotating workpiece as it removes material. A detrimental phenomenon to productivity in turning operations is unstable cutting or chatter. This can reduce the life of tooling, dimensional accuracy, and the quality of a part's surface finish because of severe levels of vibration. Ideally, cutting conditions are chosen such that material removal is performed in a stable manner. However, it is sometimes unavoidable because of the geometry of the cutting tool or workpiece. This work seeks to develop a dynamic cutting force model that can be used to predict both the point of chatter instability as well as its amplitude growth over time. Previous chatter models fail to capture the physics of the process from a first-principles point of view because they are oversimplified and rely on various "cutting force coefficients" that must be tuned in order to get a desired correlation with experimental results. The proposed approach models the process in a geometrically rigorous fashion, also giving treatment to the strain, strain rate, and temperature effects encountered in machining. It derives the forces encountered during a turning operation from two sources: forces due to chip formation and forces due to plowing and flank interference. This study consists of a detailed derivation of two new cutting force models. One relies on careful approximations in order to obtain a closed-form solution; the other is more explicit and obtains a solution through numerical methods. The models are validated experimentally by comparing their prediction of the point of instability, the magnitude of vibration in the time and frequency domains, as well as the machined surface topography during chatter.

Classical orthogonal and oblique cutting are the fundamental material removal or machining processes to which other practical machining processes can be related in the study and modelling of the machining processes. In the last century, a large amount of research and development work has been done to study and understand the various machining processes with a view to improving the processes for further economic (cost and productivity) gains. However, many aspects of the cutting processes and cutting performance remains to be fully understood in order to increase the cutting capability and optimize the cutting processes; in particular, there is little study to understand the effects of the inevitable tool wear on the machining processes. This thesis includes an extensive literature review on the mechanics of cutting analysis. Considerable work has been carried out in past decades on the fundamental analysis of 'sharp' tool cutting. Although some work has been reported on the effects of tool flank wear on the cutting performance, there is a general lack of the fundamental study of the effects of the flank wear on the basic cutting or chip formation process. It has been well documented that tool flank wear results in an increase in the cutting forces. However, it was not known if this force increase is a result of the change in the chip formation process, and/or the rubbing or ploughing forces between the tool flank and the workpiece. In work carried out since the early 1980s, the effects of the so-called edge forces have been considered when the tool is not absolutely sharp. Little has been reported to further develop fundamental cutting theories to understand applications to more relevant the practical situation, i.e. to consider the tool wear effects. Based on the findings of the literature review, an experimental investigation is presented in the first part of the thesis to study the effects of tool flank wear on the basic cutting or chip formation process by examining the basic cutting variables and performance in the orthogonal cutting process with tool flank wear. The effects of tool flank wear on the basic cutting variables are discussed by a comprehensive analysis of the experimental data. It has been found that tool flank wear does not affect the basic cutting variables (i.e. shear angle, friction angle and shear stress). It is therefore deduced that the flank wear does not affect the basic chip formation process in the shear zone and in the tool-chip interface. The study also finds that tool flank wear causes an increase in the total cutting forces, as can be expected and such an increase is entirely a result of the rubbing or ploughing forces on the tool wearland. The significance of this finding is that the well-developed machining theories for 'sharp' tools can be used in modelling the machining processes when tool flank wear is present, rather than study the machining process and develop machining theories from scratch. The ploughing forces can be modelled for incorporation into the overall cutting force prediction. The experimental study also allows for the forces on the wearland (or wearland force) and edge forces to be separated from the total measured forces. The wearland force and edge force models are developed in empirical form for force prediction purpose. In addition, a database for the basic cutting variables or quantities is established for use in modelling the cutting forces. The orthogonal cutting force model allowing for the effects of flank wear is developed and verified by the experimental data. A comprehensive analysis of the mechanics of cutting in the oblique cutting process is then carried out. Based on this analysis, predictive cutting force models for oblique cutting allowing for the effects of flank wear are proposed. The wearland force and edge force are re-considered by analysing the oblique cutting process and the geometrical relation. The predictive force models are qualitatively and quantitatively assessed by oblique cutting tests. It shows that the model predictions are in excellent agreement with the experimental data. The modelling approach is then used to develop the cutting force models for a more general machining process, turning operation. By using the concept of an equivalent cutting edge, the tool nose radius is allowed for under both orthogonal and oblique cutting conditions. The wearland forces and edge forces are taken into consideration by the integration of elemental forces on the tool flank and the cutting edge, respectively. The cutting forces in turning operations are successfully predicted by using the basic cutting quantity database established in the orthogonal cutting analysis. The models are verified by turning operation tests. It shows that the model predictions are in excellent agreement with the experimental results both qualitatively and quantitatively. The major findings, research impacts and practical implications of the research are finally highlighted in the conclusion. The modelling approach considering the flank wear effects in the classical orthogonal and oblique cutting and turning operations can be readily extended to other machining operations, such as drilling and milling.