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Consumption of energy is a key medium through which humans adversely affect their environment. Sustainable transition in the scale and composition of total primary energy demand in the 21st century is also a requirement for sustainable development of human civilisations in the face of diminishing resources of fossil fuels. One possible approach to reducing energy consumption is the energy efficient utilisation of existing energy consuming systems. This approach is less costly and time consuming than replacing the existing systems with new energy efficient ones. In addition to that, methods developed through this approach can, in principal form, be applied to more efficient future generations of systems too. Information about a quantitative measure of energy efficiency at different states of operation of a system can be utilised for optimisation of its energy consumption through computation of its most efficient state(s) of operation subject to a given set of constraints. The main contribution of this research is to develop a novel mechanistic model for energy consumption of a CNC machine tool, as an energy consuming system, in order to analytically construct a mathematical relationship between the machine tool’s overall power consumption and its operating parameters, i.e., spindle speed, feed rate and depth of cut. The analytically derived formula is experimentally validated for the case of straight slut milling of aluminium on a 3-axis CNC milling machine. The research provides evidence for substantial performance improvement in the case of the mechanistic model developed here in comparison with the currently most widely used model for energy consumption of CNC milling machines, i.e., Gutowski et al. 2006, through further analysis of the empirical data acquired during the validation experiments.

This thesis describes a theoretical and experimental investigation into the sintering of ice. When two ice spheres are brought together to touch at a point, the area of contact is found to increase with time. This phenomenon is well known in the field of powder metallurgy where it is termed sintering. The motivating force for the material . transfer is provided by the surface tension forces existing in the sharply concave region of the neck between two particles. The current theory of sintering considers four possible mechanisms for the material transfer: viscous or plastic flow, evaporation—condensation, volume diffusion, and surface diffusion. A new theory has been developed for sintering involving the transfer of material by diffusion through the environment. Measurements made on the rates of growth of the neck between spheres of polycrystalline ice and single crystals of ice are found to be in quantitative agreement with the new theory. The effect of adding impurities to the ice and changing the environmental conditions has also been investigated and the results interpreted in terms of the proposed theory. Two previous claims have been made that the sintering of ice occurs by volume diffusion and surface diffusion. These two mechanisms are analysed but the results predicted by each are shown to be at least three orders of magnitude smaller than those observed experimentally. It is concluded that surface diffusion and volume diffusion make negligible contributions to the sintering of ice and that the predominant mechanism for the growth of the neck is provided by the diffusion of water vapour through the environment.

Electrochemical machining is a process that has the potential to machine complex shapes at high production rates. However, the expansion of ECM in industry has been impeded by the iterative trial and error approach that is often required to generate process parameters for any one machining set-up. This arises due to the incompleteness of models used to describe the complex physical, chemical and hydrodynamic parameter interdependencies. Such interdependence results in non-ideal effects that distort the transfer geometry between the tool shape and the required workpiece shape. The aim of this thesis is to address some of these problems, working towards developing a predictive stoichiometric model for the chemical interdependencies of ECM that can be applied to advanced alloys and therefore further the use of ECM in industry. This has been achieved by extending the planar tool system to a segmented tool arrangement capable of measuring the chemical parameters (dissolution valencies, n, and overpotentials, V0) along the flow path length. In addition, electrolyte sampling tubes have also been incorporated into this arrangement enabling the electrolyte to be sampled along the flow path length to determine the conductivity, K and the pH. This system has been applied to the stainless steel group of alloys. A systematic study of a variety of stainless steels [SS3 16, SS4 10, Jethete (J), Duplex (D) and Super Duplex (SD)] has been performed, measuring their electrochemical machining (ECM) characteristics in chloride and nitrate electrolytes. Theoretical current-time analysis using the segmented tool was used to determine the dissolution valency, n, and overpotential, V0, along the flow path length. Electrolyte samples from the interelectrode gap, taken at intervals along the flow path, and the bulk were analysed for conductivity, pH and the soluble products characterised by visible absorption spectroscopy. The insoluble products were analysed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results indicate that the ECM dissolution characteristics of stainless steels are controlled by the surface oxide structure, which is primarily determined by the chromium content of the steel. An interesting "runaway current" phenomena was observed when machining J with nitrate electrolyte where dissolution valencies of n = 9 were observed. This phenomenon was also observed when machining pure iron. The effect was found to be caused by a short circuit reaction occurring in the interelectrode gap resulting in inefficient ECM. This short circuit problem was stopped either by using a chloride/nitrate mixed electrolyte or by the addition of a complexing agent such as EDTA. Therefore, an understanding of the dissolution chemistry has proved vital to the successful application of ECM to industrially important modern alloys.

Elongated parts make up a considerable percentage of forged components used in various industries. In many cases, their production by means of a multi-impression forging operation involves fullering and rolling processes. These are two types of open-die forging process, the main function of which is to properly distribute the metal in the longitudinal direction of the component. Several sets of empirical rules for fuller and roller die design have been proposed previously and have also been incorporated into CAD/CAM systems. Since in these processes the metal can flow freely in certain directions, there is no guarantee that the desired preform shape will be produced and some means of predicting this shape would be beneficial. During the initial stages of this project, various methods of metalworking analysis were reviewed. The model material technique and the finite-element (FE) method were selected for the analysis of the deformation during the fullering process. A gravity drop model hammer was designed and constructed for the physical simulations of the fullering process using plasticine as the model material. Ring tests were performed to find a suitable lubricant and compression tests were used to obtain the flow stress of the plasticine as a function of strain and strain rate. For the physical simulation of different types of the fullering process, a typical elongated forging component was used. These tests were performed using die shapes described as flat-flat and crowned-flat. The main features of deformation studied by the model tests were the distribution of deformation, variations of elongation and maximum sideways spread and the elongation achieved during each blow in each of the processes. The results were discussed, compared to each other and employed for the validation of the FE results. The fullering processes that were modelled physically were also simulated numerically using an elastic-plastic thermo-mechanical code (EPFEP3). Different FE models were developed to investigate the effects of mesh density on material flow. Separate sets of material properties, namely those of hot steel and plasticine, were employed in the simulations. For each set, separate FE analyses of ring compression tests were conducted to ensure that the appropriate friction condition was provided for the simulations of the fullering processes. The material flow during the fullering process, and the effects of various parameters influencing this, were investigated. To validate the results obtained from the FE simulations, they were correlated with the available experimental data as well as with the results obtained from physical modelling of the process. In most cases there was very good agreement. Also, to evaluate the empirical design rules for the forging component under consideration, the total elongation and the required minimum fuller width gained from different physical and FE simulations of various fullering processes were compared to the mass distribution requirement and to the suggestions made by some investigators. There was good agreement between various estimated fuller widths. However, it was found that to improve the amounts of total elongation, the geometries of the designed fuller dies should be modified. To avoid a trial and error method of die modification which has economical disadvantages, it was decided to employ the FE results gained from the first simulation of the process together with a numerical predictive approach. The effects of two important parameters which influence the total elongation, namely fuller gap and fuller length, were studied in the fullering process of a square bar with flat-flat dies. A method of fuller gap modification was introduced and extended to other types of fullering processes. Also, the effect of fuller length on longitudinal and transverse flow of metal was interpreted based on previous experimental observations. This investigation has also shown the feasibility of developing the current fuller CAD/ CAM system into an expert system.

During the last two decades, micromaching materials with ultrashort pulser lasers with pulse duration in the picosecond (ps) and femtosecond (fs) range opened up the possibility of material micro structuring of material removal with high precision and minimal damage. Due to the ultra-high intensity of focussed femtosecond pulses, nonlinear absorption can be induced at the focus leading to highly localised material ablation. The work presented in this thesis is primarily concerned with the process of femtosecond laser ablation or micromachining of metallic materials with a 180fs infra-red (775mm) focused laser beam.

No description available.

In the past, many papers have been presented which show that the coating of cutting tools often yields decreased wear rates and reduced coefficients of friction. Although different theories are proposed, covering areas such as hardness theory, diffusion barrier theory, thermal barrier theory, and reduced friction theory, most have not dealt with the question of how and why the coating of tool substrates with hard materials such as Titanium Nitride (TiN), Titanium Carbide (TiC) and Aluminium Oxide (Al203) transforms the performance and life of cutting tools. This project discusses the complex interrelationship that encompasses the thermal barrier function and the relatively low sliding friction coefficient of TiN on an undulating tool surface, and presents the result of an investigation into the cutting characteristics and performance of EDMed surface-modified carbide cutting tool inserts. The tool inserts were coated with TiN by the physical vapour deposition (PVD) method. PVD coating is also known as Ion-plating which is the general term of the coating method in which the film is created by attracting ionized metal vapour in this the metal was Titanium and ionized gas onto negatively biased substrate surface. Coating by PVD was chosen because it is done at a temperature of not more than 5000C whereas chemical Vapour Deposition CVD process is done at very high temperature of about 8500C and in two stages of heating up the substrates. The high temperatures involved in CVD affects the strength of the (tool) substrates. In this study, comparative cutting tests using TiN-coated control specimens with no EDM surface structures and TiN-coated EDMed tools with a crater-like surface topography were carried out on mild steel grade EN-3. Various cutting speeds were investigated, up to an increase of 40% of the tool manufacturer’s recommended speed. Fifteen minutes of cutting were carried out for each insert at the speeds investigated. Conventional tool inserts normally have a tool life of approximately 15 minutes of cutting. After every five cuts (passes) microscopic pictures of the tool wear profiles were taken, in order to monitor the progressive wear on the rake face and on the flank of the insert. The power load was monitored for each cut taken using an on-board meter on the CNC machine to establish the amount of power needed for each stage of operation. The spindle drive for the machine is an 11 KW/hr motor. Results obtained confirmed the advantages of cutting at all speeds investigated using EDMed coated inserts, in terms of reduced tool wear and low power loads. Moreover, the surface finish on the workpiece was consistently better for the EDMed inserts. The thesis discusses the relevance of the finite element method in the analysis of metal cutting processes, so that metal machinists can design, manufacture and deliver goods (tools) to the market quickly and on time without going through the hassle of trial and error approach for new products. Improvements in manufacturing technologies require better knowledge of modelling metal cutting processes. Technically the use of computational models has a great value in reducing or even eliminating the number of experiments traditionally used for tool design, process selection, machinability evaluation, and chip breakage investigations. In this work, much interest in theoretical and experimental investigations of metal machining were given special attention. Finite element analysis (FEA) was given priority in this study to predict tool wear and coating deformations during machining. Particular attention was devoted to the complicated mechanisms usually associated with metal cutting, such as interfacial friction; heat generated due to friction and severe strain in the cutting region, and high strain rates. It is therefore concluded that Roughened contact surface comprising of peaks and valleys coated with hard materials (TiN) provide wear-resisting properties as the coatings get entrapped in the valleys and help reduce friction at chip-tool interface. The contributions to knowledge: a. Relates to a wear-resisting surface structure for application in contact surfaces and structures in metal cutting and forming tools with ability to give wear-resisting surface profile. b. Provide technique for designing tool with roughened surface comprising of peaks and valleys covered in conformal coating with a material such as TiN, TiC etc which is wear-resisting structure with surface roughness profile compose of valleys which entrap residual coating material during wear thereby enabling the entrapped coating material to give improved wear resistance. c. Provide knowledge for increased tool life through wear resistance, hardness and chemical stability at high temperatures because of reduced friction at the tool-chip and work-tool interfaces due to tool coating, which leads to reduced heat generation at the cutting zones. d. Establishes that Undulating surface topographies on cutting tips tend to hold coating materials longer in the valleys, thus giving enhanced protection to the tool and the tool can cut faster by 40% and last 60% longer than conventional tools on the markets today.

Additive Manufacturing (AM) is a revolutionary technology that in recent years has become increasingly visible in mainstream media and is in the process of being developed for more widespread industrial applications. One of the challenges that has hindered the growth of AM in industry has been the aspect of surface finish, particularly in the use of Laser Sintering (LS). The surfaces produced are often perceived to be of a lower quality than those of other more traditional techniques. One of the ways in which developments have been made to address this issue is to use different post-processing techniques to achieve a variety of surface finishes. These decisions are often made by the machine manufacturers and researchers without any input from the product consumers. This thesis aims to include the consumer in the surface finish decision-making process. The main focus is to investigate the consumer perceptions of different LS surface finishes and roughness through the utilization and adaptation of human interaction and social science techniques. A group of 44 participants performed a number of blind trials on different roughness parts. It was found that up to a certain point a decrease in roughness led to a growth in perceived quality, but this increase was not infinite. All users identified roughness and smoothness as directly relating to quality; whilst other vocabulary was used to describe quality, these did not translate to “real” effects during testing. Crucially 50% of participants’ opinions of quality changed when allowed to perform a visual assessment of the parts.

This research investigates the effect of post-processing on the mechanical characteristics and behaviour of laser sintered components produced by selective laser sintering (SLS). It aims to understand the material’s behaviour and to develop postprocessing methods that can be used to improve and maintain consistency in the mechanical properties of the layer manufactured material. Duraform Polyamide (Nylon 12) and a Sinterstation VanguardTM SLS machine were used to produce test specimens. The behaviour of the layer material characteristics was established using different fabrication orientations and tensile, compression, shear and flexure tests as benchmarking investigations. The results show that there are significant variations in mechanical properties, as well as divergences from previous results. In addition, section thickness in closed and open hollow structures was investigated in order to establish its effect on mechanical properties. The larger a sintered area, the greater the tensile properties gained when there is an increase of section thickness and when solid specimens are used. Moreover, when fill and outline scanning strategies were implemented in producing the specimens, the improvements were obtained in the tensile properties of nylon 12 laser-sintered material with no impact on geometry. To further improve the mechanical properties, a new post processing method that included heat treatment in air and vacuum environments was investigated. Experiments were conducted in air from room temperature to 140oC with a treatment time of 120 minutes and vacuum heat treatment was conducted from room temperature to 180oC with 16 hours and 100 hours treatment time. The material properties in both conditions were then analysed in terms of tensile properties, thermal characterisations, microstructure and geometrical changes. Heat treatment in air showed no significant improvement in mechanical properties. However, Nylon 12 SLS material heat-treated in a vacuum showed considerable improvement in crystallinity and peak melting point. Heat treatment for a longer period to approach the melting point, especially on material with the different section thicknesses and solid specimens and particularly in a vacuum, has a greater impact on mechanical properties, but this may not be sufficient to justify the cost and time involved.