The basic layer-based manufacturing mechanism of stereolithography is built upon a scanning pattern for the entire cross section for each layer. The purpose of this research is to investigate experimentally and theoretically the effects of a new scanning pattern with the aim of improving the dimensional and geometrical performance of Stereolithography against a benchmarked industry standard scanning pattern. The development of the new Bisector scanning patterns is based on the hypothesis that a contour-oriented scanning sequence with more built-in relaxation could provide a more uniform distribution of residual stress caused by the intrinsic phase transformation due to the photopolymerization process. Experiments on a variety of geometries showed that the new scanning pattern offers substantial improvements in terms of dimensional accuracy, part flatness, surface profile and the system running cost. This further insight into the effects of the scanning patterns was gained through the use of Finite Element (FE) modelling. A commercial FE package ABAQUS was employed to develop thermo-mechanical analogous models to ~nalyse and compare the stresses, strains and distortion induced by each pattern. For the Bisector scanning pattern, the scanning direction and length of scanning vectors are more symmetrical distributed in X and Y axes and hence the distortion or curl occurs in both axes and is comparatively less than that observed for the STAR-WEAVE scanning pattern. If the same overall shrinkage is distributed in both axes then the net distortion must be reduced. The modelling results are consistent with the experimental results of this research, in that the amount of distortion on Bisector scanning patterns is less than the STAR-WEAVE scanning pattern.

The adhesion between neighbouring plant cells is established as cells are formed during cytokinesis through the middle lamella that is made principally of pectins and proteins. Pectins are secreted into the cell wall in a highly methylesterified form and subsequently de-esterified in muro by pectin methyl esterase (PME, E.C. 3.1.11). The present study reports on the biochemical characterization and immunochemical analyses of phosphate buffer/EDTA pectic extracts associated with cell-cell adhesion in suspension cultures of wild type (WT), salt tolerant (HHS) cell lines and synchronized Arabidopsis suspension cultures. Using the synchronized cultures, The PME-mediated configuration of pectins at the onset of adhesion during cytokinesis, was assessed through the analysis of the expression patterns of the PME isoforms annotated to be expressed throughout the cell cycle The wild type Arabidopsis seemed to maintain the intercellular adhesion through the gelling of the highly methylated JIM7 recognized homogalacturonans that were shown to be abundant in the primary cell walls, middle lamellae and cellular junctions, possibly due to the hydrophobic interactions between the methoxy groups. The rhamnogalacturonan-I fraction was rich in arabinan side chains reflecting the proliferative state of the cells. The increase in arabinan content was accompanied by a reduction in the galactan content 4 days after subculturing. The cell walls of salt tolerant Arabidopsis contained the JIM7 and LM7recognized epitopes along with a high degree of branching of rhamnogalacturonan-I carrying galactans and arabinans as side chains. The change in the detected epitopes is thought to play a role in the ability of the cells to withstand the high osmotic pressure and increase the in the level of adhesion between cells. The JIM5 low methylesterified HGs were less abundant in both cultures, and the absence of the 2F4 antibody recognizing the Ca2+ egg boxes could be attributed to the scarce amounts of Ca2+ present in the culturing medium The immunochemical studies of the pectin extracted from the synchronized Arabidopsis suspension cultures after washing out aphidicolin indicated that the recognition of both of JIM7 and JIM5 varied in parallel during the cell cycle, whereas, the recognition of arabinan increased during the cell division. The sequence and phylogenetic analysis of ten PME isoforms that were annotated to be expressed at one or more phases of the cell cycle of synchronized Arabidopsis thaliana suspension cultures (Menges and Murray, 2002 and 2003), revealed that only five of these genes could be PMEs. The genes At4g02330, At1g02810, At2g26440, and At2g47550 were thought to be of type II PMEs which have a pre-pro-catalytic domains and At5g47500 is a type I PME that lack the pro-region. The amino acid sequence of At4g12390 showed similarities with the N-terminal pro-peptides of plant PME and invertase inhibitors. The expression of several PME genes was studied in suspension cultures of Arabidopsis thaliana synchronised using aphidicolin. Semi-quantitative PCR experiments showed that the expression of At5g47500 transcript was always detected during M phase of the cell cycle. The rest of the genes failed to show consistent patterns of expression. Northern blots revealed that mRNA coding for At5g47500 decreases during S and G2 phases and accumulates during the M phase of the cell cycle. Our results suggest that this PME isoform is involved in the modulations of the cell walls as the cells are going through division and cytokinesis.

No description available.

High speed machining was developed over sixty years ago and at present is still limited to just a few materials, these being aluminium and its alloys, hardened steels for the mould and die industry and titanium for aerospace applications. Recently there has been additional work in high speed machining on some of the more exotic aerospace alloys such as inconel and nimonic alloys. This thesis addresses the problems encountered when machining high chromium/nickel steel alloys that are part of the stainless steel family. Three grades of stainless steel were selected for this purpose, these being a martensitic grade (416) and two austenitic grades (303 & 316). These materials were high speed milled at cuttinspeeds of up to 3,000 m min-1, via the use of two machining methodologies; high torque-low speed and low torque-high speed milling. High torque-low speed milling was accomplished through the use of specially designed large diameter dual-plane balanced face mills, that when rotated at 6,000 rev mon-1 generated a cuting speed of 3,000 m min-1. These cutters were capable of machining three grades of stainless steel at approximately ten times that of the cutting speeds normally selected for materials that are cut conventionally. However, at the elevated cutting speeds machining of the two austenitic grades of stainless steel exhibited high tool wear rates which contributed to both poor surface finish and high cutting forces.The lo torque-high speed machining of these stainless steel grades was undertaken via specifically designed variable axial rake angle cutters in conjunction with a gear-driven speed increaser. This head gave a maxiumum cutting speed of 750 m min-1 when the cutters were rotated at 20,000 rev min-1. Experiments indicated that the three grades of stainless steel could be machined at high rotational speeds, with good surface finish produced with negative axial rake angled tools. This machining strategy caused tool 'ironing' of the machined surface. cutting forces were lower at all cutting speeds when a positive axial rake angled tool was employed, although at elevated cutting speeds tool wear was excessive regardless of any axia rake angle geometry.

The main objective of the thesis is to establish a methodology to analyse the anisothermo-mechanical behaviour of a representative large industrial Superplastic Forming (SPF) tool made of XN40F material (40% Ni, 20% Cr, Balance Fe) to identify and evaluate different failure mechanisms to improve and predict the tool life. Sequentially coupled thermo-mechanical analyses under realistic loading conditions are developed within a general purpose non-linear Finite Element (FE) code, ABAQUS to predict and analyse the complex temperature-stress-strain cycles of the SPF tool. The temperature dependent cyclic plasticity and creep material data is established for the tool material performing the multi-strain range isothermal cyclic tests and the stress relaxation tests for a range of temperatures. Various strain controlled thermomechanical fatigue-creep and stress controlled ratchetting tests are designed and performed based on the preliminary FE analyses of the tool. The strain controlled and the stress controlled representative tests are carried out to capture the most damaging phase of the SPF thermo-mechanical cycle. In addition to above tests, heat transfer tests are also carried out on the rectangular block of tool material to validate the employed heat transfer methodology. Material constants are identified for different material behaviour models such as combined non-linear kinematic/isotropic hardening model for the cyclic plasticity, power law creep model for secondary creep and the two-layer viscoplastic model to address the combination of plasticity and creep. The identified constants are validated against the isothermal and thermo-mechanical fatigue tests. The FE modelling of the heat transfer tests using the calculated convective heat transfer coefficients and other thermal properties is carried out and the predicted thermal histories are compared with the experimental results. The validated heat transfer methodology is employed to simulate the realistic thermal cycles of the SPF tool. In addition to thermal loading, the tool gravity and the clamping pressure to counteract the forming gas pressure are employed in the thermo-mechanical analyses of the tool. The tool platen contact is also modelled where the platen is considered as analytically rigid surface. Various thermo-mechanical analyses are performed to investigate the effect of different thermal cycles, heating and cooling rates and the batch sizes, i.e. number of parts formed in a forming campaign, on the tool damage. Different strain and strain energy based thermo-mechanical fatigue life prediction methodologies are explored and evaluated using the isothermal and thermo-mechanical fatigue-creep lifing tests. The simple ductility exhaustion method is also developed to predict the ratchetting life of the specimen and the tool. The tool life predictions are performed employing the FE predicted stress-strain results into the identified stress-strain-life equations from the isothermal lifing tests. The predicted thermo-mechanical behaviour and tool lives are compared against the representative test and the industrial experience. From all thermo-mechanical fatigue-creep and ratchetting test results and thermo-mechanical analyses of the tool, the fatigue-creep interaction is found to be the most important factor in the tool failure.

This thesis presents new insights into gaps in the knowledge of conventional spinning and single point incremental forming (SPIF) processes through numerical modelling of their deformation mechanics. The deformation mechanics of conventional spinning is investigated by constructing finite element (FE) models of a cylindrical cup using both single and dual roller passes. A design of experiments (DOE) technique is used to generate an experimental plan based on all the relevant process parameters, followed by an analysis of variance (ANOVA) approach which is then used to determine the most critical parameters. The results indicated that the area in which most of the plastic deformation is taking place changes during the subsequent passes. The deformation mechanics of SPIF is investigated by constructing a novel dual-level finite element model of the forming of a truncated cone. The first-level FE model is validated against experimental data and the second level FE model is used to investigate the deformation modes through the sheet thickness. DOE and ANOVA techniques are used to investigate the influence of the different process parameters on the predicted through-thickness shear. Simple strategies are applied to reduce the geometrical errors without affecting the process flexibility. The results of the second-level FE model indicated that through-thickness shear is an important component in the deformation mechanism in SPIF.

Carbon fibre-reinforced polymer (CFRP) composite materials are in increasingly high demand, particularly in aerospace and automotive industries for reduced fuel consumption. This is due to their superior structural characteristics (both in fatigue and static conditions) and light weight. Anisotropic and heterogeneous features of these materials, however, have posed serious challenges in machining of CFRPs. Hence new machining technologies need to be investigated. Laser is a non-contact (eliminating toolwear) thermal process. Therefore, the thermal properties of the material are of crucial importance. Especially for composite materials which consist of different constituent materials. In CFRPs, carbon fibres are excellent conductors of heat (thermal conductivity of 50 W/(m.K)) while the polymer matrix is poor conductor (thermal conductivity of 0.1-0.3 W/(m.K)). This significant difference that can be similarly traced for other thermal properties such as heat of vaporisation and specific heat capacity are the source of defects in laser cutting of CFRP composites. Major quality challenges in laser cutting of these materials are delamination and matrix recession. Various laser systems and cutting techniques are investigated in this work to minimise these defects. Multiple-pass cutting using a high beam quality continuous wave (CW) mode fibre laser is found to be effective to minimise delamination at low power level and high scanning speeds. Multiple-pass cutting using nanosecond pulsed DPSS Nd:YAG laser is shown to reduce matrix recession. A novel technique using mixing of reactive and inert gases is introduced and demonstrated to minimise the matrix recession. In order to improve the quality and dimensional accuracy of CFRP laser machining, it is important to understand the mechanism of transient thermal behaviour and its effect on material removal. A three-dimensional model to simulate the transient temperature field and subsequent material removal is developed, for the first time, on a heterogeneous fibre-matrix mesh. In addition to the transient temperature field, the model also predicts the dimensions of the matrix recession during the laser machining process.

In the modern global economy, there is a demand for high precision in manufacture as competitive pressures drive businesses to seek greater productivity. This results in a demand for a reduction in the errors associated with CNC machine tools. To this end, it is useful to develop a greater understanding of the mechanisms which give rise to errors in machine tool drives. This programme of research covers the geometric, thermal and load errors commonly encountered on CNC machine tools. Several mathematical models have been developed or extended which enable a deeper understanding of the interaction between these errors, various details of ballscrew design and the dynamic behaviour of ballscrew driven systems. Some useful models based on the discrete matter or “lumped mass” approach have been devised. One extends the classical eigenvalue method for finding the natural frequencies and other dynamic characteristics of ballscrew systems to include viscous damping effects using a generalised eigenvalue approach. This gives the damping coefficient of each predicted vibration mode along with the estimates of the natural frequencies, enabling many of the natural frequencies predicted by standard undamped natural frequency analyses to be dismissed as being of little consequence to the vibratory behaviour of the system. A development of this modelling method gives the sensitivity of the system to changes in stiffness and damping characteristics, which is helpful at the preliminary design stage of a ballscrew system, and is an aid in deciding the most convenient remedy to vibration problems which may occur in service. The second set of lumped-mass models is specially developed to take account of the changes in the configuration of the system with time as the nut moves along the screw while taking into account the non-linear phenomena of backlash and Coulomb friction. These can deal with the axial, torsional and transverse degrees of freedom of the system and predict many aspects of the dynamic behaviour of a ballscrew system which have an effect on the errors arising from such systems. They also include features which calculate the energy converted to heat by all the energy dissipative mechanisms in the model which can be used in conjunction with models already developed at the University of Huddersfield to predict thermal errors. Further, a strategy for compensation of some of these errors has been devised

The requirement for improved dimensional accuracy to achieve ever tightening tolerances in manufactured parts increases the need for high precision machine tools. Machine tool accuracy is affected by various errors from which thermal errors have been identified as one of the largest contributors. These are primarily caused by heat generated by the machine as it operates and exogenous influences, mainly in the form of varying environmental temperature, that result in deformation of the machine structure. There is a complex interaction between the structural components having different heat sources, thermal time constants and thermal expansions and therefore the combined effect on tool position accuracy is often non-linear and difficult to correct easily. There has been considerable research effort to model this behaviour, usually based on temperature information, to compensate the induced errors. The methods and techniques have proved their capabilities with excellent thermal prediction and compensation results but they often require significant effort for effective implementation constraints for complexity, robustness, cost and time consumption. One of the most significant resources required is thermal testing on the machine and can be the main obstacle for the implementation of many of such methods for industries where production machine availability cannot be compromised. This research provides a method where the machine downtime can be reduced significantly using offline simulation techniques for extended and complex real world machine operations. In this research FEA is used to simulate the thermal behaviour of the entire structure of a small milling machine using Abaqus/CAE Standard FEA software. In order to ensure accurate simulations, heat source parameters need to be obtained for which an efficient methodology was created to calculate body heat flux values from a short test. Additionally, a study was conducted to understand the heat flow mechanism across structural joints requiring Thermal Contact Conductance (TCC) values. This research contributes experimentally obtained, and therefore accurate, TCC values for structural interface conditions compatible with CNC machine tool joints not previously available. This was followed by the investigation of the thermal behaviour of the machine due to both internal heat and external environmental fluctuations. A broad range of operating and static stability tests were conducted to validate the FEA modelling strategy for simulating the thermal behaviour of the machine for internal heating and environmental temperature fluctuations. The simulated and experimental movement of the tool matched by more than 60% in all cases; and by more than 70% in most cases. The most significant cost benefits from this project may result from understanding behaviour during the long and very long term simulations that are impractical or unfeasible to complete experimentally. This information facilitates capability assessment and model development. Within this research, simple linear models compatible with existing compensation capabilities in modern NC systems was targeted. Extracted FEA data is used to identify temperature-displacement sensitive areas within the full machine structure. The identification method locates structural nodes whose temperature change correlates with error at the tool to effectively install temperature sensors permanently at those positions for simple linearly correlated thermal error compensation.

Micro drilling has been applied in the interconnection and precision manufacturing industries extensively. As a promising machining technique, Ultrasonically Assisted Drilling (UAD) has become increasingly popular in both academia and industry in recent years. In this thesis, modelling techniques and experiments for Ultrasonically Assisted Micro Drilling (UAMD) are investigated. Representative work on modelling of micro drills and UAD has been documented and categorised. Existing gaps in the literature are identified and the aims of this research are formulated. Using the Finite Element (FE) technique, a hybrid model is developed to realise modelling for the whole drill bit without compromising the computation efficiency, even when the drill has a complicated geometry (small diameter flute, multiple step shanks, etc). A specific drill model (Φ0.3 mm diameter, 2 step shanks) is chosen for a case study in order to evaluate the model. The hybrid tool shows sufficiently accurate results and impressive computation efficiency in the evaluation. For vibration modelling, force modelling and experimental work, a standard Φ1 mm drill with 1 step shank is used across the chapters. First of all, FE analysis is conducted on the whole drill and normal modes are solved with boundary condition as fixed simply supported. A 2 Degree-of-Freedom (DOF) model is then built considering rotation and the ultrasonic excitation to solve the transverse vibration with boundary conditions consistent with the FE model. The asymmetric geometric characteristics of the drill bit are taken account of through using the first two fundamental modes in the FE model. Potential parametric resonances are discussed in the numerical simulation. Other vibration characteristics are also discussed with varying parameters such as ultrasonic frequency, ultrasonic amplitude and rotational speed. In order to extend the vibration model, a nonlinear thrust force model has been developed for incorporation into the 2 DOF model. The force model considers ultrasonic parameters, feed rate, material properties and the nonlinearity of the UAMD process. Force reduction during the UAMD process is explained qualitatively with the model and a full range of feed rates have been simulated to study their effect on the force reduction. The limitations of this model have also been explained. A high speed UAMD system was designed to examine the effects of key parameters. Experiments with different ultrasonic frequencies, amplitudes and rotational speeds were conducted and the influences of these parameters on thrust force were investigated. With the thrust force data from these experiments, a correlation study to the simulation results based on the force model is carried out. The study identifies the limitations on the current one dimensional force model and leads to recommendations for the further development of the force model. Further work is identified for both modelling and experiments, and the present models can be expanded to suit the research and development of UAMD techniques.