Laser metal deposition is an additive manufacturing technique to build fully dense structures with a strong metallurgical bonding with the underlying material. Spherical gas-atomised metal powders are principally used as build material which is a costly option and restricts its application on a wide scale. On the other hand, nonspherical particles produced by machining are much cheaper to produce and readily available as waste swarf which should be recycled. The use of machined particles as a viable form of build material for laser direct metal deposition has not been explored previously and is the subject of the investigations reported in this thesis. In the first work, samples of carbon steel machining swarf in three size ranges were laser deposited to build thin walls. The produced walls exhibited fine martensitic microstructure with minimal porosity. As general trends, individual deposition tracks were found to be lower, and wider with an increase of particle size. 50% reduction in hardness was observed when using coarser particle size. This work was extended so as to build U-shaped structures with variable laser power in contrast to the previous work which was done with one set of processing parameter values. The microstructure observed was similar to that of the previous work. However, hardness has found to increase with decrease in laser power. After successful deposition and encouraging results from the process, machining swarf of Inconel 617 was used to produce corrosion resistant layers on a mild steel substrate. A Design of Experiment methodology was used to analyse the relationship between the processing parameters and the coated layer characteristics. The layer thickness and hardness were found to increase with the mass feed rate whilst an increase in laser power produced the opposite result. All layers had a predominantly dendritic microstructure and displayed remarkably higher corrosion resistance than the mild steel sample. The work was expanded to investigate the surface characteristics and corrosion resistance in a harsh corrosive environment, using different pH brine solutions. In this investigation, four layers were produced with two laser power and mass feed rate values. Accounting for all measurements, Inconel 617 swarf built layers provided very good corrosion protection and confirmed the viability of using this method as a low-cost corrosion protection for both mild and harsh environments. Since the investigations authored above were confined to swarf alone, the final chapter examines the comparison of stainless steel 316L thin wall structures produced with swarf and gas-atomised powder using similar processing conditions. The build materials performed similarly, but walls made from swarf were slightly shorter with a coarser microstructure and had poorer corrosion resistance than the powder equivalents.The results of these investigations confirm the feasibility of machining swarf as an alternative viable option. However, further research will help to explore its full potential.

The H21 and H23 tungsten hot working tool steels are used at elevated working temperatures due to their resistance to softening, high hot hardness, and high compressive strength. The mechanical properties of these tool steels are strongly affected by the presence of carbides. High concentration of carbide forming elements in these tool steels tends to form brittle eutectic carbide networks. Carbide networks in the as cast condition are detrimental to their mechanical properties. The objective of this study was to identify controlled thermomechanical processing (TMP) parameter, namely deformation temperature at two different solutioning temperatures to break down carbide networks and improve hardness. The primary focus of this research was on the H21 tool steel owing to its promising hardness after TMP. The H21 tool steel was double tempered after TMP to improve its toughness. For comparison purposes, conventional heat treatment was also performed on both tool steels. The TMP process was an axisymmetric compression test at a constant true strain rate of 0.01 s-1, that was performed at 1000, 1050 and 1100 °C after solutioning at 1100 or 1250 °C. Double tempering was carried out at 650, 750 and 800 °C, with air cooling in between the first and second temper. The solutioning and double tempering temperatures in the conventional heat treatment were the same as for the TMP samples. An overview of the flow curves and the characterisation of microstructures showed no evidence of dynamic recrystallisation. The increase in flow stress with decreasing solutioning and deformation temperatures was attributed to dislocation movement and the presence of fine and dispersed carbides causing a Zener pinning effect. The peak stress, microstructure and hardness data indicated that the optimum hot deformation condition was solutioning at 1250 °C and deformation at 1100 °C. No secondary hardening occurred after double tempering the H21 tool steel samples that were first subjected to hot deformation. The highest double tempered hardness (354 HV) of the H21 tool steel occurred after double temper at 650 °C following solutioning at 1250 °C and subsequent deformation at 1000 °C. It is suggested that the operating temperature for the H21 tool steel with the conditions used in this study should be less than 650 °C.

Additive Manufacturing (AM), popularly called “3D printing,” has benefited from many two-dimensional (2D) printing technology developments, but has yet to fully exploit the potential of digital printing techniques. The very essence of AM is accurately forming individual layers and laminating them together. One of the best commercially proven methods for forming complex powder layers is laser printing, which has yet to be used to directly print three-dimensional (3D) objects above the microscale, despite significant endeavour. The core discovery of this PhD is that the electrostatic charge on toner particles, which enables the digital material patterning capabilities of 2D laser printing/photocopying, is disabling for building defect-free 3D objects after the manner attempted to date. Toner charge is not mostly neutralized with fusing as previously assumed. This work characterizes and substantiates the accumulation of residual toner charge as a primary cause for defects arising in 3D printed bodies. Next, various means are assessed to manage and neutralize residual toner charge. Finally, the complementary implementation of charge neutralization with electrostatic transfer methods is explored.

Traditional manufacturing methods like moulding or subtractive manufacturing place significant limitations on structures which could be manufactured in a single process. These limitations can now be overcome by a new manufacturing technology—Additive Manufacturing (AM), which provides the users much more freedom to design and produce structures in one piece. Additive manufacturing refers to a range of processing technologies, which fabricate 3D parts by adding successive layers. With this technology, complex 3D structures can be produced directly following the production of a geometric data. Additive manufacturing also enables production without the need of tooling, which brings the prospect of a revolution in the manufacturing industry. Material jetting is one of the additive manufacturing techniques, which generates material layers through inkjet printing. This technology also allows the user to build structures consisting of more than one material, which further expands the capability of additive manufacturing to include the production of multi-functional products. However, due to the strict requirements on the rheology of usable inks, there is a limited number of materials available for use in this technology. This research aims to develop a novel polycaprolactone based ink which is suitable for material jetting and could be potentially used for fabricating scaffolds. The bespoke nature of these devices often require a complex structures, customized design and small batch sizes, which all together make the product costly when using the traditional manufacturing methods. Additive manufacturing technology can reduce these costs, in the main due to the nil marginal cost (e.g. tooling cost, mould design etc.) when changing product design. In addition, material jetting can also incorporate multi-materials or multi-functional devices, mixing several materials at micron level, potentially enabling more advanced and intelligent functions to be incorporated into the final devices. In this project, Polycaprolactone (PCL), commonly used for its biodegradable properties, was investigated as a candidate for material jetting. Both solvent based and UV reaction based jetting techniques were attempted to build up an understanding of the aspects and parameters involved in material jetting ink development and jetting parameter optimization. For solvent based PCL ink, PCL flakes were dissolved into various solvents with different concentrations to prepare a low viscosity ink which could be printed. Volatility, viscosity and surface tension were investigated to confirm that the prepared ink was suitable for jetting. PCL with 5wt% in 1,4-dioxane was successfully jetted by using a Dimatix material printer. A range of experiments were carried out to investigate the ink’s printability under different conditions. During the study, efficiency limitation for solvent based ink was also realized. In order to meet the printing viscosity limit of the inkjet printheads, the loading level of a solute in a solvent ink as well as the efficiency of stacking precipitated layers were both restricted. This curbed the possibility of solvent based ink be applied in making large 3D parts. For UV reaction based inks, the printed ink can fully solidify to form structures after UV illumination, which overcame the processing efficiency limitation of the initial solvent based inks. Pure PCL is not UV curable and therefore chemical modifications were made to graft UV curable functional groups into the PCL structure. The rheology of synthesized UV curable PCL polymers were studied and modified to make them suitable for material jetting. Different photoinitiators were also investigated to work out the suitable composition to achieve real-time curing. Oxygen inhibition was found to be the main side effect which inhibited the curing reaction in an air environment. Type II photoinitiators can help overcome this effect and 3D structures were able to be obtained in both air and nitrogen. It was also found that a nitrogen environment can improve the properties of the printed specimens and the printed samples showed better hardness and modulus than those in printed in air. It was also noted that the increasing concentration of the photoinitiator can improve the curing speed of the ink printed in air. However the samples with higher concentration of photoinitiators manifested a reduction of hardness and modulus. A post-curing procedure, carried out using further UV illumination, was shown to help improve both the hardness and the modulus, but this improvement was limited to the directly illuminated surface.

Abstract In modern manufacturing environments waste is an issue of great importance. Specifically the research in this thesis looks at issues in establishing the initial steps to gain a generic process monitoring system that ensures that grinding is both optimised but not the determent where costly malfunctions mean the scrapping and re-melting of expensive quality intensive materials. The research conducted in this thesis investigates the process of cutting, ploughing and rubbing during single grit scratch tests. These investigations meant the correlation between physical material removal phenomenon and the emitted material dislocations gained from acoustic emission extraction. The initial work looked at different aerospace materials and the distinction of cutting, ploughing and rubbing during single grit radial scratch tests. This initial work provided novel results not seen in this area before and paved the way for more robust results in investigating the same phenomena during horizontal single grit scratch tests. This work provided more robust classification of cutting, ploughing and rubbing and transferred directly to grinding pass cuts from 1um and 0.1mm depth cuts respectively. In using robust classifiers such as the Neural Network and novel classifiers such as non-linear data paradigms, Fuzzy-c clustering with Genetic Algorithm optimisation, cutting, ploughing and rubbing phenomenon was investigated. These investigations showed that more cutting occurs when there is moreinteraction between grit and workpiece based on the increase depth of cut. Other thesis results investigated a generic classifier using Genetic Programming to classify multiple anomaly phenomena. This work can be bridged together with the unit event grit classification work.

In recent decades there has been a rapid development of technology in manufacturing industries, in particular through the increasing use of ever more powerful and sophisticated Computer Numerical Controlled (CNC) machines to manufacture complex parts. These machines are supported by a chain of computer based software solutions amongst which manufacturing information is exchanged. With the need for information exchange, interoperability between various computer-aided systems (CAx) has become an important research area. In CNC part programing, innovations by various hardware manufacturers and their reflection in their software have led to the necessity for the existence of different part programs for each machine. Creating these is a time consuming and economically inefficient activity. Implementing genuine interoperability between CNC machines is a way of eliminating this deficiency but, to achieve this, CNC programmers must be able to write a CNC program for a specific machine and effortlessly convert that program to work for other machines. The aim of this research was to enable the exchange of CNC programmes across machines with different technologies and demonstrate this between a C-axis CNC turn-mill machine and a 4-axis CNC machining centre. This has been achieved by designing a cross-technology interoperability framework that is capable of supporting systems that can work with the different types of CNC machines. This framework is the core contribution to knowledge from this PhD research. In order to fully identify the context for the research, this thesis presents a review of existing literature on machining of turn-mill parts and interoperability for CNC manufacturing. This is followed by the specification and realisation of a novel framework for cross-technology interoperability for CNC manufacturing. The demonstration is conducted using test components that can be manufactured using different CNC technologies.

No description available.

In the last two decades, technological progress towards the miniaturisation of products and components has increased significantly. This trend has also been driven by demands for the manufacture of devices with functional features on the nanoscale. One of the nanofabrication processes, which has been proposed by researchers to meet such needs, relies on the mechanical machining of the surface of a workpiece with the tip of an atomic force microscope (AFM) probe. In this case, the AFM probe is utilised as a cutting tool as it enables the direct contact between its sharp tip, which is fixed on a flexible micro cantilever, and the workpiece surface. A relatively large numbers of studies have been reported in the field of AFM tip-based nanomachining since the invention of the AFM instrument itself just over thirty years ago. However, such studies have typically neglected the fact that AFM probes should be considered as flexible tools when investigating this process. Thus, this shortcoming constitutes the main motivation behind this PhD research. Following a review of the literature, the work reported in this Thesis starts by a study of the bending orientation of cantilevers during AFM tip-based nanomachining operations along different processing directions. To achieve this, an advanced experimental set-up is developed first in order to monitor a number of output signals, which characterise the motions of both the fixed and the free ends of the cantilever together with the displacements of the AFM stage. A refined theoretical analysis is also presented to express the bending orientation of an AFM probe cantilever at its free end as a function of the forces acting on the tip when machining in a direction pointing away from the probe. This refined model shows that the bending orientation depends on both geometric parameters of the cantilever and on the cutting forces. Complementary experiments, which are designed to determine the quasi-static bending behaviour of cantilevers in practice, show that, contrary to assumed knowledge, both concave and convex bending orientations could take place when machining along this direction. The occurrence of a change of the cantilever deflected shape from convex to concave bending during machining can principally change the depth and width of grooves produced. For instance, the depth of grooves machined on a single crystal copper specimen may increase up to 70% following this phenomenon. iv Following this, another refined model is also developed to measure the normal force acting on the tip when the AFM stage is static by taking in account the cantilever geometry and its inclination angle with respect to the sample surface. This work leads to the introduction of a correction factor that should be applied when using the conventional equation for determining the normal load in this configuration. Results obtained when implementing this model based on the dimensions of typical commercial AFM probes show that the conventional approach always leads to an underestimation of the normal applied force. In addition, it is demonstrated, both theoretically and experimentally, that the conventional method for determining the applied normal load during AFM tip-based nanomachining, i.e. when the stage is not static, is wrong. Based on this shortcoming, a novel procedure is proposed to estimate all three force components (i.e. thrust, axial, and lateral forces) acting on the tip during AFM tip-based nanomachining. To achieve this, two novel methods are also developed to assess the actual value of normal force during machining, which in this case is referred to as the thrust force. Based on experimental data, a good agreement is found between both methods for different physical quantities evaluated. Another refined theoretical model, based on the classical beam theory, is also employed in this procedure to determine the axial force acting on the tip and subsequently, the lateral force. Using this novel procedure to estimate the cutting forces, it is also shown that even if the deflection angle at free end of probe is constant, this does not mean that the associated cantilever vertical deflection is constant between the configurations when the AFM stage is static (i.e. for nanoindentation) and when it is moving (i.e. during an actual cutting operation). Finally, in order to gain further insights into the material removal mechanisms that influence the process, a series of post-machining investigations on the topography of produced grooves is reported for different applied loads and processing directions. This particular experimental study takes advantage of the prior knowledge established in this Thesis. Indeed, the understanding of the cantilever deflected shape and the accurate assessment of cutting forces provide key inputs when the groove formation process is analysed.

Atomic force microscope (AFM) probe-based mechanical nanomachining has been considered as a potential low-cost alternative method for the generation of nanoscale features on the surface of components and devices. Therefore, it is important to understand the factors that influence the tip wear of AFM probes in order to achieve reliable and accurate machining operations when implementing this process. Despite the fact that the basic applicability of AFM probe-based machining has been demonstrated for many years, studies focussing on the wear of the tips as a function of processing conditions are relatively scarce. In addition, the accuracy and practical suitability of in-situ techniques to monitor the condition of AFM probes is not adequately acknowledged. To address these issues, a series of experimental studies were conducted in this PhD research when implementing the AFM probe-based machining process on a single crystal copper workpiece at selected values of applied normal loads, machining distances and for different machining directions. First, the assessment of the wear of AFM silicon probes was carried out based on two dimensional (2D) tip profile data. This particular study also presented a simple method for improving the accuracy of the tip wear assessment procedure when conducted on 2D profiles. Next, AFM silicon probes with diamond-coated tips were used as cutting tools for a different range of applied normal loads and along various processing directions. For this particular study, the AFM probes wear assessment relied on two different three dimensional (3D) in-situ measurement techniques, namely the ultra-sharp tip scan approach and the reverse imaging method. Reliability and practical suitability aspects between these two in-situ techniques were also assessed and discussed. For each set of experiments, different qualitative and quantitative ii wear metrics were observed and analysed. Particularly, from the qualitative perspective, the evolution of the AFM tip apex profiles along selected machining distances and directions was considered. As for the quantitative measurement, tip radius and tip volume loss measurements were estimated. The most important findings reached in this study are given as follows. First, it was shown that the error associated with the traditional method of assessing the tip volume from 2D profiles could be 26% in comparison with the simple method proposed here. In addition, among the 3D in-situ AFM probe characterisation methods considered, the reverse imaging approach was judged to be the most reliable technique. This study also showed that tips in silicon were very prone to initial tip fracture during the AFM probe-based nanomachining process. This phenomenon could also take place, albeit to a lesser extent, when silicon tips coated with diamond were utilised. When the nanomachining process is not in control due to such tip fracture, it is difficult to extract firm conclusions about the influence of the processing parameters on the tip wear. Besides, this rules out the application of a design of experiments approach where the minimisation of the tip wear volume may be the objective. The study also showed that the AFM probe-based nanomachining process was more likely to be in control when using silicon tips coated with polycrystalline diamond with no nitrogen doping. In this case, a much reduced likelihood of tip fracture could be achieved accompanied with negligible tip wear. In addition, the associated results suggested that the evolution of the tip wear was not equal in all machining directions investigated, with the largest wear occurring in a direction parallel and away to the cantilever long axis. The reason for this should be due to the fact that this was also the direction where the process was most likely to be conducted in the ploughing-dominated regime. Finally, when the nanomachining process was realised in iii control, the wear volume was seen to increase with the increase in the normal load for all directions considered.

Abrasive micro-waterjet processing is a non-conventional machining method that can be used to manufacture complex shapes in difficult-to-cut materials. The constant development of new materials with enhanced properties has sparked the interest in alternative machining technologies. Among these non-conventional machining methods, Abrasive Waterjet Machining is regarded as a flexible technology with potential to cope with a wide range of materials and applications. The use of a soft tool (i.e. the jet) is very advantageous because it makes it possible to perform different operations without modifying the equipment. However, this advantage poses a significant challenge: the erosion power of the jet is controlled through a set of operating parameters, and it is therefore necessary to have a deep understanding of the relation between such parameters and the effect of the jet on the surface. The process itself is subject to strong random variations, and this makes it even more complex to develop a detailed understanding of the optimum strategies to control the jet. The main objective of this thesis is to develop mathematical frameworks that account for the stochastic nature of the process, and that have the capability to predict detailed statistical information of the eroded surfaces for different operating parameters. This is addressed with two modelling approaches: a finite element model where the system is regarded as a set of multiple particles hitting a workpiece at very high speed, and a geometrical model built on the idea of considering the abrasive waterjet as a generic energy beam and exploiting the geometrical properties of the system. In the Finite Element approach, a modelling framework with the capability of predicting the average shape of abrasive waterjet machined footprints and the variability along the trench has been developed for the first time. This is achieved by combining finite element analysis and Monte Carlo methods, and the model is validated at different feed speeds and tilt angles. The random nature of the system is included by considering the input parameters (i.e. size, relative orientation, or position within the jet of the abrasive particles) as random variables with associated probability distributions. The geometrical approach is a method to predict the variability of the jet footprint for different jet feed speeds. Since the objective is to incorporate the stochastic nature of the system in the model, a stochastic partial differential equation is used to describe the machined surface as the jet is moved over it. This framework is greatly advantageous because it can be used to make fast predictions of the variability of the trench profiles (to within < 8%), and it can therefore be implemented into CAD/CAM packages. The modelling work, focused on the understanding of how the operating parameters changes the effect of the jet on the surface, is accompanied by an experimental study to uncover how the material properties of the workpiece will affect the erosion process. This is carried out by machining trenches on model materials (i.e. materials with the same chemical composition, but different grain size), and performing and in-depth analysis of the material response, which shows how the machining process has a strong impact on the microstructure of the target material. The work developed in this thesis contributes to the understanding of the erosion process during abrasive waterjet machining and how stochastic methods can be used to enhance the current capabilities of this technology.