Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2005. / Includes bibliographical references (leaves 81-86). Also available in electronic version.

M.Ing. / This report documents the steps taken to gain insight into the phenomena of high speed machining (HSM) of titanium alloys. This was done by firstly studying titanium alloys and the problems associated with machining titanium alloys. An experimental set-up and procedure was developed for measuring and recording both the machining temperature and component forces. A sufficient set of experimental data was collected through extensive experimentation. The cutting temperatures and component forces in HSM of Ti-6Al-4V were examined simultaneously. The cutting speed was found to be the most influential and limiting parameter on the machining temperature and component forces. A new approach for modeling the temperatures in HSM of titanium alloys was developed. Analytical predictions of the cutting temperatures were performed and used to evaluate the influence of a variation in the process parameters on the cutting temperature. The research provides insight for future work into the phenomena of HSM of titanium alloys . The results of the analytical model were found to be representative and comparable to the experimental data. It is however expected that the deviation between the predicted and measured result may be significantly reduced by changing the experimental approach. It is recommended that a complete set of experiments be done, using a new tool insert for every cut, thus removing the effect of possible tool wear on the experimental data obtained. In addition it is recommended that the iterative solution be improved through more in depth programming, considering the change in both the thermal and mechanical materials properties with a change in temperature. Ultimately the assumptions made in order to simplify the problem addressed in this report needs to be improved upon, in order to analyze data trends and even magnitudes to a greater degree of certainty.

The high speed machining is now recognized as one of the key manufacturing technologies. It possesses several better characteristics than those of a conventional machining way. For example, low chip load, and low cutting-heat generation can be obtained. It also contributes to high productivity and throughput. In this thesis, the technique about the high speed machining for cutting the aluminum thin-walled components will be discussed. An audio signal measuring system will be established to measure sound pressure for avoiding chatter. Meanwhile, the tool path will also be revealed in this thesis.

M.Ing. / This dissertation documents the stages involved in determining the parameters that define surface integrity. Chapter one gives a basic introduction to the project; the problem statement; scope of work and project obstacles. This chapter laid down the requirements for the literature study in Chapters two and three. The literature study discusses machining, high-speed machining, titanium alloys and high speed machining of titanium alloys. Information from the literature study was used to determine the experimental program presented in Chapter 4. Two materials were investigated in this study: grade 2 titanium (commercially pure) and grade 5 titanium (an alloy containing 6% Aluminium and 4% Vanadium). A fixed feed rate of 0.25mm/rev was selected. Two depths of cut were used: 0.2mm and 1mm. Cuts were performed both lubricated and un-lubricated. Different cutting speeds were used both inside and outside recommended ranges. Surface roughness tests, optical microscopy, scanning-electron microscopy, microhardness tests and x-ray diffraction were used in the experimental program. Results obtained presented trends seen in previous work on surface integrity. Efforts were made to reduce errors in obtaining and examining data. Conclusions were drawn with regards to each surface integrity parameter tested for. It was found that different cutting speeds affect each surface integrity parameter differently.

Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references (leaves 230-235). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references (leaves 230-235). Also available on the Internet.

M.Ing. (Mechanical Engineering) / Titanium and its alloys have the potential to serve as a strategic economic driver of the South African economy. The manufacture and use of high strength, lightweight materials such as titanium alloys have become of great importance in the aerospace and biomedical industries over the past few decades. The manufacturing costs of titanium alloy components however, are considered high due to the poor machinability of the material. Furthermore, as with all metals during machining, surface residual stresses are induced into the material. These are of particular interest in the aerospace industry as they can be either detrimental or beneficial to the performance and fatigue life of materials. The aim of this investigation is therefore to examine the effect that machining parameters have on the magnitude, sign and distribution of residual stresses induced in Grade 4 and 5 titanium alloys during high performance machining (turning). The effect of these machining parameters is investigated by residual stress measurements conducted with X-ray diffraction and grain structure analysis of the machined surfaces by optical microscopy. Results show that cutting speed and depth of cut have a significant effect on the residual stresses. At low cutting speeds, the surface residual stresses are largely compressive, becoming more tensile with an increase in cutting speed. An increase in depth of cut also introduces more compressive residual stresses into the material. The microstructural analysis of the alloys shows that grain deformation decreases with an increase in cutting speed and cutting depth.

M.Ing. (Mechanical Engineering) / High strength alloys such as titanium are widely used within applications that require specific material properties. These include high strength, high temperature as well as low weight applications. Thus a need arises to investigate the fundamental to understand the mechanics of how these materials are machined. Titanium alloys are known for the difficulties that arise during the machining thereof. Complexities arise due to its inherent material properties, the most important property being the retention of strength at high temperatures. In addition to maintaining its strength, it becomes highly chemically reactive with other materials at increased temperatures. All these factors contribute to extreme temperatures at the tool chip interface contributing to increased tool wear and shortened tool life. The aim of the research is to investigate the effect of machining on various cutting process parameters including cutting force, temperature, tool wear and surface finish for grade 2 and grade 5 titanium alloys during high speed turning. Grade 2 titanium is a commercially grade with lower mechanical properties, while Grade 5 is titanium alloy with substantially higher mechanical properties and is the most widely used titanium alloy. In addition an experimental setup was developed and verified to conduct fundamental research on the high speed machining of titanium alloys. A literature review was concluded with focus on the machining of titanium alloys. This was followed by the development of the experimental setup, measurement and compilation of data. The data was compiled into graphs and compared with the current research available. The research found that for the cuts performed, that cutting forces are independent of cooling applied and that no substantial variation was noted between the two grades. When temperatures were evaluated, dramatic drops in temperature were noted when coolant was applied. As temperatures increased, specifically during un-cooled cutting, the inserts deteriorated having an effect on the quality of the surfaces obtained. When coolant was applied, substantial temperature drops were achieved, improving tool life and directly improving surface finishes. The best surface finish was achieved for higher cutting speeds as and lower feed rates. This phenomenon was found for both grades of titanium evaluated. The largest amount of tool wear was noted for the highest cutting speeds, with increased values noted for Grade 5 in comparison with Grade 2. This phenomenon is noted for crater as well as flank wear.

Manufacturing by mechanical machining has historically benefited from the use of cutting fluid. Cutting fluids help to reduce temperature, friction, flush away chips, and hence prolong tool life and improve machining performance. However, uncontrolled use of cutting fluid raises concern in respect of cost and environmental burden. For these reasons, dry machining is used in conjunction with high speed machining to reduce cycle times and simultaneously deliver a greener process. However, for some workpiece materials full implementation of dry machining is not economically viable due to the absence of the essential cooling and lubricating functions delivered by cutting fluids. The most feasible bridging technology is minimum quantity lubrication (MQL) where a very small flow rate of coolant/lubricant is delivered to the cutting zones. In terms of machinability, the application of MQL is promising. However, most studies conducted on MQL focused on the feasibility of MQL application and show-casing the technical benefits. No studies had been identified in literature systematically investigating the relationship between cutting conditions and MQL with the goal of optimising the process. Moreover, the presumed environmental benefits of MQL have not been systematically assessed because Life Cycle Analysis (LCA) derived evaluation models do not explicitly model the impact of machining conditions such as feedrates, cutting velocities and depth of cut.The motivation for this PhD work was to select the optimum machining process variables for maximising effectiveness of MQL, to explore process improvements and to assess the environmental credentials of the process in relation to other forms of cutting environments. In this work, high speed, end milling tests on tool steel were undertaken and 1) Taguchi methods were used to optimise the process, 2) the sensitivity of tool wear to nozzle position was evaluated and 3) the environmental burden of dry, MQL and flood coolants were evaluated based on direct energy needs and process outputs. A fluid soaking device was used to assess the amount of fluid collected or presumed to be delivered to the cutting zone for different nozzle orientations.The Taguchi process optimisation suggested that in HSM the size effect, brought about by a low chip thickness, should be considered in the search for an optimum process window for HSM. A significant and novel finding of this PhD was the dominance of MQL nozzle positioning. The study clearly showed that when machining hardened steel at a high cutting speed and RPM the tool life could be significantly increased by 50% by adjusting the position of the nozzle toward the rake face in relation to the end-milled face. The work opens up new science and provides recommendations as to where to align the nozzle when end milling tool steel at high cutting speeds. The fluid trapping and the blade-wiping angle are key parameters that influenced the effective delivery of MQL when high spindle revolutions per minute are used. These results from the fluid soaking device were found to correlate strongly with observed machining performance evaluations.In terms of modelling, the PhD developed an improved and more generic direct energy model that can be used to determine the environmental burden for direct electrical energy requirements and the energy embodied in other process material outputs. This model addresses the system boundary and activity that within the control of the manufacturing plant. The model was used to evaluate the environmental performance of dry, flood and MQL fluids. The impact of these results and models in optimising environmental performance was also illustrated.The work in this PhD is important to industry in that it contributes to the optimisation of MQL and gives an assessment of the environmental impact. The PhD developed new and significantly important machining science in the positioning of nozzles in MQL machining at higher speeds.

M.Ing. / Grade 4 titanium is a commercially pure grade titanium alloy extensively used in various industries including the chemical industry and more recently in the biomedical industry. Grade 4 has found a niche as a biomedical material for production of components such as orthopaedic and dental implants. Its physical properties such as high corrosion resistance, low thermal conductivity and high strength make it suitable for these applications. These properties also make it hard-to-machine similar to the other grades of titanium alloys and other metals such as nickel based alloys. During machining of titanium, elevated temperatures are generated at the tool-workpiece interface due to its low thermal conductivity. Its high strength is also maintained at these high temperatures. These tend to impair the cutting tool affecting its machinability. Various investigations on other grades of titanium and other hard-to-machine materials have shown that machining at high cutting speeds may improve certain aspects of their machinability. High speed machining (HSM) is used to improve productivity in the machining process and to therefore lower manufacturing costs. HSM may, however, change the surface integrity of the machined material. Surface integrity refers to the properties of the surface and sub-surface of a machined component which may be quite different from the substrate. The properties of the surface and sub-surface of a component may have a marked effect on the functional behaviour of a machined component. Fatigue life and wear are examples of properties that may be significantly influenced by a change in the surface integrity. Surface integrity may include the topography, the metallurgy and various other mechanical properties. It is evaluated by examination of surface integrity indicators. In this investigation the three main surface integrity indicators are examined. These are surface roughness, sub-surface hardness and residual stress. White layer thickness and chip morphology were also observed as results of the machining process used. The effect of HSM on the surface integrity of grade 4 is largely unknown. This investigation therefore aims to address this limitation by conducting an experimental investigation on the effect of HSM on selected surface integrity indicators for grade 4. Two forged bars of grade 4 alloy were machined using a CNC lathe at two depths of cut, 0.2mm and 1mm. Each bar was machined at varying cutting speeds ranging from 70m/min to 290m/min at intervals of approximately 20m/min. Machined samples were prepared from these cutting speeds and depths of cut. The three surface integrity indicators were then evaluated with respect to the cutting speed and depth of cut (DoC). iv Results show that a combination of intermediate cutting speeds and low DoC may have desirable effects on the surface integrity of grade 4. Highest compressive stresses were obtained when machining with these conditions. High compressive stresses are favourable in cases where the fatigue life of a material is an important factor in the functionality of a component. Subsurface hardening was noticed at 0.2mm DoC, with no subsurface softening at all cutting speeds. Surface hardness higher than the bulk hardness tends to improve the wear resistance of the machined material. Though surface roughness values for all depths of cut were below the standard fine finish of 1.6μm, roughness values of samples machined at 0.2mm DoC continued to decrease with increase in cutting speed. Low surface roughness values may also influence the improvement of fatigue life of the machined components. These machining conditions, (intermediate cutting speeds and low DoC), seem to have promoted mechanically dominated deformation during machining rather than thermal dominated deformation. Thermal dominated deformation was prominent on titanium machined at DoC of 1mm.