Controlling uncertainties is a challenging aspect in design and manufacturing of microsystems. As microsystems are characterised by features in the micro domain, product development and manufacturing processes are applied at the boundaries of their operational areas. In combination with many disciplines (mechanical, electrical, software, chemical etc.) and little standardisation, it causes microsystems development to be more time and cost intensive than products in the macro domain. Development of microsystems benefits from a concurrent approach of product and production design. Uncertainties may be addressed by application of methods for systems engineering (engineering design). Systems engineering applies models for the analysis of projects, usually a linear set of gates that need to be closed successively as the project evolves. Over the last ten years, models with an iterative approach of design and testing, gained in popularity due to their more agile characteristic that performs better in fast changing markets. Microsystems development benefits from the linear approach that performs well for their structured project control, but because of the high market dynamics, agile methods will speed up the process, which results in faster market introduction, advances the product life cycle, and increases return on investments. Currently, there are no known systems engineering models that combine linear and iterative monitoring of projects to gain the best of both methods, especially not in combination with the capability of concurrently monitoring the development of product and production design. This thesis investigates how existing ways of system engineering can be combined to: (RQ1) enable iterative and linear modelling of microsystems development, and (RQ2) merge these qualities into a combined model to monitor the development process concurrently. The first problem is addressed by (RQ1): i. Modelling development progression by execution of iterative cycles that alternately perform functional system decomposition and functional gating. ii. This iterative model is elevated with the method of Axiomatic Design to enable concurrent system decomposition. Implementation of elements from the V-Modell XT enable functional gating to index the concurrent development process iii. The ‘Theory of Complexity’ of Axiomatic Design is applied to realise an intelligent, knowledge based, gating function to be used as a continuous maturity measure; The results show that linear and iterative models can be merged successfully. With some extensions, the Theory of Complexity of Axiomatic Design can indeed be used for continuous monitoring of product and process development. The thus-obtained maturity measure can be applied for the analysis of project decisions. This was successfully done for retrospective analysis of two cases. To merge the qualities of analyses ‘i to iii’ into a combined model to monitor the development process concurrently, three tools for application have been developed (RQ2). iv. The first is a method for visualisation of the intelligent gating function, based on analysis ‘iii’. The method applies a newly developed ‘Maturity Diagram’ that plots the Design Axioms as continuous parameters v. The second is a method for assessment of reconfigurable manufacturing systems based on analysis ‘ii’. The method estimates the investigations needed to (re)configure a product specific manufacturing system vi. The third is a tool for roadmapping and monitoring that combines outcomes of analyses ‘i, ii, and iii’. This model is called ‘Constituent Roadmap’ and it is based on: (a) an iterative approach, (b) concurrent decomposition, (c) the advanced gating function, and (d) knowledge application to the product and process design. The Constituent Roadmap was applied for the development of a ‘smart dust’ sensor system. It was found to structure knowledge development and application. This increases the chances to satisfy the functional requirements of the design. In parallel, it functions as a communications tool between designers and managers. Together, a reasonably complete picture has emerged how the design of microsystems and their production means can be modelled, and how uncertainties may be categorised so they can be addressed in the best order.

Milling of Carbon Fibre Reinforced Polymer (CFRP) is necessary for component accuracy prior to assembly of aircraft. Recently, ultrasonic assisted milling (UAM) which combines conventional machining (CM) with ultrasonic vibration on the cutting tool, has shown beneficial outcomes with respect to the machinability of some metals, however, limited UAM of CFRP has been reported. In this thesis, milling (CM and UAM) of a CFRP incorporating Bismaleimide 5250-4 (BMI 5250-4) resin was carried out in a wide range of cutting parameters and environments (dry, conventional cutting fluid (CCF) and CO2 cryogenic). Machinability was examined in terms of tool wear, cutting forces and surface roughness. In terms of machinability with conventional cutting tools, machining in a CO2 had a positive effect on tool life, despite an increase in cutting forces, compared to CCF and dry. UAM was found to reduce cutting forces by up to 10 %, compared with CM, however, this did not yield any benefit in terms of tool wear and/or workpiece surface roughness. When dry machining employing an abrasive diamond tool, CFRP material adhesion was a feature. The application of UAM in this instance yielded, reduced workpiece adhesion on the cutting tool and improved workpiece surface roughness. Machining of CFRP must be performed below the glass transition temperature (Tg) of the resin to avoid the degradation of the properties of the matrix resin. In this research new findings in the temperature initiated during machining and the consequential effects on the polymer utilised Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) which is well established in polymer characterization. FTIR and DSC was carried out to investigate the effect of machining on the chemical and material properties of BMI 5250-4 such as Tg and changes to matrix resin chemical bonding, which has been closely associated with degradation of the machined part. Further analysis of the machined surface by DSC indicated that the Tg of the matrix resin had been exceeded during the machining process and led to degradation of the BMI 5250-4 in some cases. An observed reduction of the maleimide double bond (C=C) at 825 cm-1 wavelength by FTIR signified that further post-curing of BMI 5240-4 had occurred which suggested that a higher cutting temperature was developed at the machine tool tip than recorded with the infrared camera. CM dry machining, FTIR analysis also confirmed the formation of isocyanate-derived products (C≡N) at 2250 cm-1 wavelength, a bond associated with the point at which BMI 5240-4 is thermally degraded having experienced temperatures in the range 400 to 600 °C. This result suggests that when CM dry machining the actual cutting temperature experienced by the BMI 5240-4 was at least 400 °C. The formation of isocyanate-derived products was not observed for UAM dry machining, suggesting that ultrasonic vibration of the cutting tool may reduce the cutting temperature in the primary shear zone, however this temperature reduction was insufficient to arrest observed post curing effects and shift in the Tg. Other aspects of the FTIR analysis revealed that despite the improvements to workpiece surface roughness when milling with CCF there was an increased presence of moisture (-OH bond) in the BMI 5240-4 resin which may have a detrimental effect on the durability of the material over time. Machining CFRP has been enhanced by the introduction of the chemical analysis. It suggests that DSC and FTIR exploration of the thermal history of the CFRP can provide more information about the temperature than typical thermal measurement during machining such as thermal cameras and thermocouples. The management of the milling process of CFRP can now be related to the management of the temperature at the tool tip and the effect on polymer characteristics. As a consequence, milling of CFRP in CO2 exhibited improvement in tool wear, an observed reduction in cutting temperature, and sustenance of the chemical properties of BMI 5250-4. However, there was no significant benefit in additionally employing UAM in a CO2 environment. The research has provided a new insight in the milling of polymer composites and could be beneficial in avoiding thermal degradation of the machined part, maintaining the quality of machined part and avoiding scrap parts at the end of machining processes.

The present study is concerned with the development of an inverse analysis of the depth-sensing indentation test based on a multi-objective function (MOF) optimisation model. The input data of this model are the load-displacement (P-h) curve extracted from the indentation instrument and the surface topography of the residual imprint left by the indenter after the removal of the load measured via atomic force microscopy (AFM). A Swift’s power law material model was considered to represent the indented material and thus, the output of the optimisation are the Young’s modulus (E), yield stress (σy) and strain-hardening exponent (n). The optimisation problem was designed to minimise the error between both the experimental and predicted P-h curves, i.e. the first objective, and pile-up profiles, i.e. the second objective, with the aim of addressing the non-uniqueness of the inverse analysis of indentation. A 3D FE model of the depth-sensing indentation test has been developed in ABAQUS in order to generate the predicted data from a set of trial material properties, i.e. E, σy and n. The generation of FE input files (pre-processor) and extraction of FE output files (post-processor) have been automated through MATLAB and Python subroutines. The optimisation problem was solved by the trust-region reflective algorithm available in the MATLAB Optimization ToolboxTM and thus, concisely, the model minimised the experimental and predicted data by modifying iteratively the material properties, starting from the initial guess properties specified by the user, until convergence was reached. Upon convergence, the material properties were said to describe the elastic-plastic behaviour of the indented material. A comprehensive experimental programme was carried out in order to investigate the load dependency of the indentation response of three different materials, including a steel (CrMoV), a titanium alloy (Ti-6Al-4V) and a high-purity copper (C110). The study of the topography of the residual imprints provided a better understanding of the effects of the microstructural arrangement on the plastic displacement of material beneath the indenter. The extent of piling-up was observed to be very sensitive to the difference in material properties from grain to grain and the crystallographic plane of the indented grain. Furthermore, it was concluded that the structural arrangement of the indented material may also contribute to the asymmetry observed in the pile-up profiles, in particular in materials with large grains relative to the projected area of the indenter, e.g. C110. This piece of work therefore, is suggested as a guideline for the use of height measurements of the residual imprint in the characterisation of the plastic behaviour of materials. The multi-objective function optimisation model is proved to be a step forward to the characterisation of the near-surface properties as, in contrast to the P-h curve, the residual imprint is strongly linked to the plastic behaviour of the indented material. Therefore, the physics governing the indentation problem were better represented. Therefore, the optimised P-h curve provided a very good fit to the corresponding experimental curve, to within an error of less than 2.4% and 8.4% the maximum (hmax) and residual (hr) depth, respectively, for all three materials, CrMoV steel, C110 copper and Ti-6Al-4V. Furthermore, a deviation of less than 12.4% was achieved between the area of indentation provided by the FE model and AFM instrument. Additionally, the value of maximum peak height (hpeak) was predicted with a maximum error of 11% in relation with the experimental pile-up profiles. Therefore, it was concluded that the optimised solution provided a very good representation of the complex mechanical response to indentation such that the volume of plastically displaced material as predicted by the optimised FE model was observed notably in accordance with experimental measurements. Furthermore, the complementary information provided by the second objective function allowed the model to distinguish between different materials showing identical indentation response – referred to in the literature as ‘mystical’ materials. In addition, a key outcome of this investigation suggested that stress-strain curves generated by mechanical tests performed at different scales, exhibit similar behaviour with only the magnitude of the stress increasing or decreasing depending upon the scale. Part of this thesis is dedicated to the application of the proposed inverse analysis for the characterisation of three phases located across the joint of a like-to-like inertia friction weld of SCMV steel, including martensite in the tempered, quenched and over-tempered condition. This study, characterised the generation of residual stresses into two stages: the thermal strain dominated initial cooling period that accounts for the majority of the residual stresses, and the phase transformation strain dominated final cooling period. In addition, it was concluded that at the onset of transformation from austenite to martensite, the volumetric changes experienced in the lattice relax up to 70% of the predicted tensile hoop stress found in the vicinity of the weld line near the inner surface and that the interaction of soft regions of austenite and hard regions of heat unaffected martensite accounts for up to 17% of the peak tensile stress. The indentation response of the set of optimised properties that represent each of the phases, was in very good agreement with the corresponding P-h curve and residual pile-up profile extracted from the indentation instrument and AFM, respectively. The capability of the inverse analysis to build the stress-strain relationship in the elastic-plastic regime using the optimised mechanical properties of the parent metal has been validated using experimental data extracted from the compressive test of an axisymmetric sample of tempered martensite [1]. The inclusion of the softer over-tempered martensite phase allowed the FE prediction to determine the proportion of the heat affected zone (HAZ) comprised by each phase in better agreement with the experimental weld-trial. Based on the interpretation of the microhardness test performed across the weld, the harder region formed due to the quenching process extends approximately 54% the length of the HAZ, whereas the rest 46% is comprised by the softer over-tempered martensitic phase. According to the FE prediction, the heat affected zone was composed by a proportion of 57% quenched martensite and 43% over-tempered martensite. Moreover, the distance from the weld line to the region where martensite fully tempered was observed to extend 79 and 71% the length of the HAZ, as determined by the FE model and experimental measurements, respectively. The presence of a softer region, OTM, between two harder regions, namely QM and TM, relaxed 7 to 11%, 1 to 6% and 12.8 to 15.3% the peak values of stress in the radial, axial and hoop directions respectively. A key observation from the results of the FE prediction was that the peak hoop residual stress is located at the boundary of the quenched and over-tempered martensite, and not at the edge of the heat affected zone. This observation was in agreement with the residual stress measurements published by Moat et al. [2].

This study shows that an all-thermoplastic (nano- or micro-fibre) polymer can be created using coaxial electrospinning to create fibre mats akin to pre-impregnated fabric, which can be formed into a composite without the addition of other materials. This has not yet been accomplished by using the coaxial electrospinning production process. Experimentation to investigate the maximum fibre volume ratio found that these composites were successfully formed at 0.73 fibre volume fraction, which is higher than the maximum found in traditionally formed composites (0.60 – 0.70). The formation of the composite from the fibre mats was investigated, and found that the composites formed at the lowest temperature and pressure (70 °C and 1 bar) exhibited the higher tensile strength, up to 84 % higher than at other temperatures and pressures. Higher pressure and temperature caused deformation in the reinforcing fibres, resulting in lower tensile strength. The composites were shown to have more consistent Young’s modulus and higher tensile strength compared to a composite made from the same materials, but with the fibres and matrix materials produced separately, and combined during the composite forming procedure. The finalised composite produced in this research exhibited an average Young’s Modulus of 2.5 GPa, ultimate tensile strength of 33.2 MPa, and elongation at break of 3.8 %.

Additive Manufacturing (AM) encompasses several different technologies, such as inkjet printing, extrusion, and laser melting processes, to selectively transform a processable phase, such as a liquid or powder, to a solid phase, e.g. through solidification, chemical reaction or powder melting and solidification. The geometry is initially defined as a 3D CAD model, which is subsequently ‘sliced’ to create a geometrical representation suitable for the layer-wise manufacturing process. These layers are “printed” in series on a substrate and are additively stacked. Some AM processes can also include multiple materials or voids in this process to increase the design freedom and geometric complexity. With any new process there are challenges, the key one for most AM processes is the limited material selection. Different processes have different material requirements and many current AM materials are sourced from other processes, for example a number of stereolithography processes use materials originally developed as finishes or coatings. The various AM processes have different criteria that must be met for a material to be suitable for processing, such as particle size and distribution, melting temperature and laser absorption in the case of laser-powder bed systems. This PhD is concerned with materials for ink jet printing, a major advantage of this process being the capability to co-deposit different materials. As the materials in jetting are not fed from a single bed or on a platform, there is complete control over material placement. The basic technology behind material jetting is the same as that seen in desktop inkjet printers, and the major challenge in transforming this to a 3D printing method is in materials development. Currently, the process is dominated by fast curing UV based resins, which are primarily acrylate based, and solvent based inks. The solvent inks highlight their 2D printing origins as they have a low material loading resulting in thin layers. These solvent systems are typically used to transport a conductive solute e.g. silver nanoparticles or graphene oxide. The focus of this PhD was to develop new materials for AM jetting by combining reactive components during processing. This process, called Fully Reactive Inkjet Printing (FRIJP), is only possible because of the freedom of material jetting to use multiple materials. In this work two reactions were selected for the development of FRIJP inks. The first was the crosslinking of polysiloxane based polymers (PDMS), the second was the addition polymerisation of polyurethane. These two reactions schemes were chosen because they involve the combination of two different reactive species and produce no unwanted by-products. For the FRIJP of PDMS a commercial two-part chemistry was used that separated the cross-linker and catalyst. When these two components are combined they produce a transparent PDMS rubber. The PDMS was found to have a viscosity that was too high for inkjet printing so a compatible solvent was selected and the concentration modified. Once a printable ink had been created, trials were conducted which involved printing the two components onto a substrate. It was found that by control of the mixing ratio and substrate heating, high reaction rates could be achieved and complex designs could be printed. These designs were then analysed using FTIR and Raman spectroscopy and it was found that there was comparable curing to the bulk mixing. It was also determined that for the selected PDMS there were no issues with substrate mixing which would result in concentration gradients. The second reaction investigated was the addition polymerisation of polyurethane, which involves combination of the diol and diisocyanate. For this work, the inks were developed from monomers that had printable viscosities through thermal modification. However, one ink used did contain a low concentration of solvent. For the polyurethane work the printing environment was controlled to minimise the moisture which could produce unwanted polyurea and amines. The metric used to determine how suitable the inks were for inkjet printing was the molecular weight of the polymer chain. The analysis was conducted using Size Exclusion Chromatography on the printed samples. It was found that after in development, it was possible to achieve an average molecular weight over 20,000, which was identified as the point whereby the polymer printing was successful. This PhD also demonstrates that when printing these two chemistries, the small size of the droplets facilitates complete mixing of the inks. Importantly, with the immiscibility of the polyurethane monomers before reaction, it was found that the small droplet size allowed for the reaction and successive molecular diffusion to achieve the high degrees of conversion required for the production of functional polymers.

Modern manufacturing organisations face a number of external challenges as the customer-base is more varied, more knowledgeable, and has a broader range of requirements. This has given rise to paradigms such as mass customisation and product personalisation. Internally, businesses must manage multidisciplinary teams that must work together to achieve a common goal despite spanning multiple domains, organisations, and due to improved communication technologies, countries. The motivation for this research is to therefore understand firstly how the multiplicity of stakeholders come together to realise the ever increasing and ever more complex number of product variants that manufacturing systems must now realise. The lack of integration of engineering tools and methods is identified to be one of the barriers to smooth engineering workflows and thus one of the key challenges faced in the current dynamic market. To address this problem, this research builds upon previous works that propose domain ontologies for representing knowledge in a way that is both machine and human readable, facilitating interoperability between engineering software. In addition to this, the research develops a novel Skill model that brings the domain ontologies into a practical, implementable framework that complements existing industrial workflows. The focus of this thesis is the domain of industrial assembly automation systems due to the role this stage of manufacturing plays in realising product variety. Therefore, the proposed ontological models and framework are applied to product assembly scenarios. The key contributions of this work are the consolidation of domain ontologies with a Skill model within the context of assembly systems engineering, development of a broader framework for the ontologies to sit within that complements existing workflows. In addition, the research demonstrates how the framework can be applied to connect assembly process planning activities with machine control logic to identify and rectify inconsistencies as new products are introduced. In summary, the thesis identifies the shortcomings of existing ontological models within the context of manufacturing, develops new models to address those shortcoming, and develops new, useful ways for ontological models to be used to address industrial problems by integrating them with virtual engineering tools.

Laser powder bed fusion offers many advantages over conventional manufacturing methods, such as the integration of multiple parts which can result in significant weight-savings. The increased design freedom that layer-wise manufacture allows has also been seen to enhance component performance at little or no added cost. However, for such benefits to be realised, the material quality must first be assured. Laser ultrasonic testing is a non-contact inspection technique which has been proposed as suitable for in-situ monitoring of metal additive manufacturing processes. The thesis presented here explores the current capability of this technique to detect manufactured, seeded and process generated sub-surface “defects” in Ti6Al4V samples, ex-situ. The results are compared with X-ray computed tomography reconstructions, focus variation microscopy and destructive testing. Whilst laser ultrasound has been used to successfully identify a range of material discontinuities, further work is required before this technique could be implemented in-situ.

The continuous increase of Turbine Entry Temperature (TET) in aerospace gas-turbines is the main driver for the research effort in the development of coatings for thermal and oxidation protection: i.e. Thermal Barrier Coatings (TBC). The need for TBC is particularly relevant within the combustor assembly (or simply combustion chamber) where the highest temperatures within a gas turbine, in excess of 1700 C, are registered. Due to the harsh thermal and oxidative conditions experienced within the combustion chamber, TBC are subjected to several degradation mechanisms which generally result in spallation (or delamination) of the coating. Spallation is more likely to be observed at specific locations within a combustion chamber, and acceptance limits for this quantity are specified by the Original Equipment Manufacturer (OEM). To reduce the risk that coating spallation will lead to an unplanned engine removal, in-situ coating re-deposition may be possible. However, the development of such a technology poses significant challenges. The selected deposition process must, in fact, be able to operate in a confined environment (i.e. the combustion chamber) and produce TBC of microstructure providing adequate thermal and oxidation protection properties. Moreover, a deep understanding between the process parameters and both microstructure and shape of produced coating is necessary to achieve an optimum control over the whole deposition process. Therefore, after an initial selection of Combustion Flame Spray (CFS) as TBC deposition technology, the present thesis has the following objectives: (i) analysing in-depth the physics/chemistry of coating build-up at a microscopic level (i.e. single-splat) in order to relate this to fundamental properties (e.g. adhesion and residual stress) measured at macroscopic coating level, (ii) investigating the relationship between process parameters and their effect on the material properties of the deposit, in order to determine an optimum process parameters "window" and (iii) to develop a mathematical framework that accounts for the stochastic nature of the deposition process, and has the capability to predict the deposit growth geometry with high spatial accuracy for different process parameters. For coating build-up analysis purposes, a novel set of experimental tools is developed, allowing to model fundamental flattening and solidification mechanisms with a sub-micrometre spatial resolution. For deposition parameters optimisation purposes, an extensive experimental analysis of the effect of deposition parameters including: powder morphology (size and shape), equivalence ratio, powder feed rate, carrier gas flow and torch-to-substrate standoff distance has been performed for the CFS-produced TBC to complete the lack of knowledge in literature data. Finally, the deposit growth model allows to predict, in the time domain, the three-dimensional footprint (i.e. deposit shape) and temperature of CFS and generally thermal spray deposits. For this purpose, a three-dimensional implicit finite-difference algorithm, based on two interplaying geometrical and thermal-analysis sections, has been developed. The work of this thesis thus provides a step forward in the understanding of the thermal spray deposit formation process. In fact, the determined correlation between properties at both single splat and coating level represents a powerful tool making the optimisation of process parameters-coating properties relationship more efficient as opposed to traditional trial-and-error approaches. Moreover, the developed calibration-based deposit growth model results of simple application, opening the way for spray automation in difficult-to-spray geometries and/or repair applications for several thermal spray processes.

Drawbeads control the flow of material into the die cavity during pressing operations. The tribological and forming properties of aluminium necessitate specific frictional and drawbead geometry requirements that are different from those established over many years for steels. Academic research on this topic is limited, requiring industry to rely on trial and error methods to determine the coefficient of friction and drawbead geometry. This research project focused on developing an innovative, scientific and holistic methodology to determine the optimum drawbead geometry and an appropriate coefficient of friction value to be used in forming feasibility simulations for aluminium panels. Special attention was given to the ease with which this research could be implemented in an industrial environment. Hence, extensive experiments to gather material properties such as plane strain and pure shear tests, complex material models, or optimisation models based on artificial neural networks (ANN), and non-linear friction models were avoided. Three approaches identified in the literature for designing drawbeads, namely, experimental, analytical and numerical modelling were investigated to test the underlying assumptions, strengths and limits of each. For example, analytical models assumed symmetric material flow passing over the drawbeads, which in reality does not occur. Based on these findings a systematic, hybrid approach has been developed which uses a combination of physical drawbead tests and numerical modelling, to determine the coefficient of friction which is then used to obtain the drawbead restraining force. Using a novel criterion, different drawbead geometry conditions have been ranked to aid selection of an optimised drawbead geometry. The optimised drawbead geometry obtained from the hybrid approach was validated by stamping of rectangular pans. The rectangular pan, when stamped using the optimised geometry obtained from the hybrid approach, did not show defects such as severe thinning and wrinkles. The numerical stamping model with geometric drawbead predicted the punch force with a 4.5% error, thinning with a 5% error and draw-in with an 8% error. An innovative hybrid approach has been proposed which is capable of accurately predicting the coefficient of friction, the drawbead restraining force and the drawbead geometry. The same coefficient of friction and the drawbead geometry when used in the forming simulation accurately predicted the punch force, thinning and draw-in. As a direct application of innovation, Jaguar Land Rover can use the novel criteria for selecting the drawbead geometry to use effectively the drawbead geometry generation feature in the commercial sheet metal forming software package during forming feasibility simulations. The hybrid approach can potentially save 34% of the die tryout time and provide average cost savings of £34,400 per die set per tryout attempt.

Ching-hung Lai. / Thesis (M.Ph.)--Chinese University of Hong Kong. / Bibliography: leaves 218-224.