Weight reduction in body-in-white structures is necessary to make automobiles more fuel-efficient. A range of high and ultra-high strength strip steels have been developed, that will play a key role in achieving lower weights since the steels have the potential to achieve equivalent strength and crashworthiness at thinner gauges. However, the full potential of these advanced alloys can only be realised if they can be integrated into production facilities that rely on resistance spot welding as the predominant means of component joining. In particular, spot welds manufactured in these modern high strength steels will need to meet the strength and fracture resistance requirements that are based on automotive manufacturers' familiarity with low alloy steels. Dual phase steels are a range of modern alloys causing considerable excitement due to their combination of high strength, high ductility and improved crashworthiness in automotive components, compared to mild steel. Their commercial production routes rely on a metallurgical understanding of how chemical composition and thermomechanical treatments interrelate to produce appropriate microstructures. Their often complex alloy compositions mean that there is potential for significant changes to take place in the microstructure on resistance welding. This research programme has considered the important relationships from which resistance spot-welds, produced in high strength steels, derive their properties. This includes an investigation into the continuous cooling transformation behaviour of four dual phase alloys, in comparison to low alloy grades, and measurement of the mechanical properties associated with their microstructures. The thermal profiles generated within spot welds have been measured using a thermocouple technique. Advanced resistance spot welding processes, that can modify the metallurgical condition of a spot-weld, have been investigated with some success, both in terms of reductions in weld hardness following pulsed welding schedules, and an understanding of the effect of such schedules on the thermal cycle.

Aluminium extrusion is a forming process used for manufacturing straight and long aluminium products. Among all aspects of the process, extrusion die design is the key issue for producing high-quality extrudates. The approaches to design extrusion dies can be broadly classified into three groups; trial and error, empirical based approach and numerical simulation based approaches. By using the first two methodologies, the quality of extrusion die designs are intrinsically and strongly linked with designers' experience and skill. As the required forms for extrusions become more complex, these two approaches becomes less useful. Besides, since the design knowledge is held by designers, it is more often a 'black art', and the personnel movement can influence the design work significantly. On the other hand, with the advent of computers and greatly enhanced computing capability, many new approaches have been introduced for designing extrusion dies in last few decades. However, even with the current computing power, the numerical simulation approach has its limitations, particular in time required and even accuracy. Extrusion process involves complex constitutive relationships and large deformation of material. To overcome the limitations posed by current available design approaches, a new geometry based methodology has been proposed in this thesis. The new methodology combines empirical design formulae, geometry reasoning technique and optimization algorithm together. The work originates from the earlier work done by Miles et al. [1, 2, 3, 4], and Armstrong and his colleagues [5, 6, 7, 8, 9, 10, 11, 12], In this research work, a new knowledge representation scheme is developed so that historical data can be easily gathered and reused. By using empirical bearing length design formulae with historical data, a new bearing length estimation approach is introduced so that new profiles can be designed based on past good designs. A novel die layout design approach has also been developed and validated. This new method uses bearing length estimation algorithms with maximum bearing length difference to give radial or fiat layout for single/multi-hole dies. By using medial axis transform, a set of new geometry reasoning algorithms have been studied. These algorithms give a general and robust way to analyze two-dimensional geometry shapes. A brand-new die profile categories have been proposed to avoid the drawbacks held by current classification. A new algorithm and a set of new classifying criteria have been introduced. Based on medial axis transform and geometry reasoning technique, extrusion die profiles can be classified into different category correctly and efficiently. This research work shows that all the proposed approaches give several feedback paths in extrusion die design process. Therefore, not only historical data can be reused for new designs, but it is also possible to acquire and represent design knowledge and to optimize the whole design process.

Several major algorithmic and modelling aspects of the discrete element method are presented, with particular effort made to establish a general framework for the combined finite/discrete element simulation of shot peening and peen forming processes. On the basis of a general review of the contact detection algorithms, the alternating digital tree (ADT) and the augmented spatial digital tree (ASDT) are presented as examples of tree based search algorithms; whilst the dynamic cell based search algorithm is presented as an example of cell/grid based search algorithms. Extensive numerical tests are provided to compare the performance of the approaches discussed and to perform a parametric study of the dynamic cell algorithm. Contact resolution for circular and spherical discrete objects is comprehensively discussed. Following the establishment of geometric relations between contact pairs, four interaction laws for the normal contact are reviewed, together with a general analysis of the equivalence between them. A modified classic Coulomb friction model is proposed for 3D contact problems, and a new time stepping scheme is developed to ensure both short and long term stability of the contact models. In addition, two different schemes that incorporate energy dissipation into the contact model are reviewed. A new approach is proposed for contact resolution of 2D superquadrics. An advancing front technique based algorithm is described to generate a random packing of disks, ellipses and polygons; whereas a geometric based compression algorithm is developed to generate a random packing of spheres of various sizes within a geometric domain. A general algorithmic framework is established for the combined finite/discrete element analysis of shot peening processes, particularly for the evaluation and comparison of several interaction laws governing the contact between shot and workpiece. The proposed model is also verified with the experiments conducted elsewhere. A two stage combined finite/discrete element and explicit/implicit solution procedure for the simulation of peen forming process is developed, and verified with experiments.

Tube hydroforming has already proved successful in sub frame and chassis applications. However, there has been limited uptake of this technology in the production of BIW structural components. Mainly due to the fact that standard tube making methods are restricted to production of tubes with a diameter to thickness ratio of 65:1 at best, where as typical BIW application would be more inline with a ratio of 100:1. The Corus Tubular Blank process enables a greater range of D/t ratio, and therefore a larger scope of manufacture for BIW parts. The major technical issue concerned with the manufacture of both Corus Tubular Blanks and Corus Tailor Welded Tubes (Corus Tubular Blanks made using LWTB’s sheets) is the effect of material elastic recovery after forming has taken place. It has been well documented in previously published literature that the magnitude of elastic recovery (springback) in a component is influenced by the material and forming properties. It is very difficult to have full control of the material properties. However, forming properties are controllable especially if the forming process is simple as in the case of the Corus Tubular Blank. Corus Tailor Welded Tubes introduce a complex combination of springback characteristics inherited from the constituent parent parts of the LWTB. This thesis provides a method of springback prediction, as well as indication of the important factors associated with springback. Highlighted is the ability of springback to be mitigation via means of increased forming force, in conjunction with the ability to predict the subsequent springback behaviour.

No description available.

The main aim of the work described in this dissertation has been to develop a description of the interface between the chip and the rake face of a cutting tool. This interface is of great importance in many manufacturing operations. The experiments are conducted in a vacuum planing machine, which provides precise control of the atmospheric conditions during cutting. The chip/tool interface is studied directly, using a transparent (sapphire) cutting tool to machine various ductile metals, such as lead and aluminium, in air and in vacuum. On the basis of these observations a new classification is made of the zones of contact at the interface in continuous cutting. This description is extended to steel tools and harder workpieces such as copper. The influence of oxygen on the rake face interaction is investigated. Previous workers have noted apparently anomalous behaviour; it is suggested that recent discoveries about the adhesion between metals and oxides help to explain these anomalies. The transparent tool is used to study the access of cutting lubricants to the chip/tool interface and the role of lubricants is examined in the light of the new description of the interface. Continuous cutting with built-up edge formation, experienced with materials such as Duralumin and steel, and discontinuous cutting, experienced with materials such as magnesium and free-machining brass, are studied by means of these new techniques. Some suggestions are made concerning the material properties responsible for these types of cutting behaviour. The conditions of contact at the rake face of the tool are also studied. A study is made of the influence of crystallografhic orientation of the workpiece on the cutting process. Pure single crystals of aluminium, copper and magnesium are machined in various orientations. Some speculations are also made about the source of the instability in continuous cutting and on the mechanism of chip curl.

No description available.

In recent years there have been significant new developments in welding processes for joining stainless steel and dissimilar metals. This is associated with the rise in interest of using stainless steel in the automotive industry from both car manufacturers and stainless steel producers. The main reason for using stainless steel within the automotive industry is the combination of formability and high strength but also the improved corrosion resistance when compared to zinc coated mild steel. This research explores the mechanical and metallurgical properties of dissimilar metal joining and determines a relationship between the fatigue properties and weld geometry. The research focuses on the relatively unexplored joining techniques of Laser Hybrid Welding and Cold Metal Transfer applied to joining stainless steel grades Hy-Tens 1000 and LDX 2101 to Dogal 260RP-X mild steel. The joints are assessed in terms of tensile, fatigue and metallurgical properties. Experimental results and analysis show that the fatigue properties of both laser hybrid welding and cold metal transfer joints are a linear relationship with a negative gradient to value of the root angle on the mild steel side of the joints, as the angle at the root decreases the fatigue life increases. It was found that when joining the material combinations outlined in this research with Laser Hybrid Welding the resulting solidified weld pool was chemically inhomogeneous. However, welds produced using Cold Metal Transfer resulted in a chemically homogenous weld pool and consistent microhardness. Comparisons with laser welding show that laser hybrid welding and cold metal transfer can produce joints with mechanical properties comparable to welding methods currently being used in the automotive industry, for example, laser welding.

Manufacturing functional prototypes and different tools using conventional methods usually is a time consuming process with multiple steps. The global economic pressure to get products to market faster has resulted in the development of several Rapid Prototyping (RP) techniques. Layer manufacturing technologies are gaining increasing attention in the manufacturing sector. They have the potential to produce tooling either indirectly or directly, and powder metal based layer manufacture systems are considered to be an effective way of producing rapid tooling. Selective Laser Sintering (SLS) is one of several available layer manufacture technologies. SLS is a sintering process in which designed parts are built up layer by layer from the bottom up using different powder materials. A laser beam scans the powder bed, filling in the outline of each layer’s CAD-image by heating the selected powder pattern to fuse it. This work reports on the results of an experimental study examining the potential of the selective laser sintering process to produce metallic parts using stainless steel powder. One material, a stainless steel powder and one sintering station research machine, which was constructed in Leeds, were used during the research. A step-by-step investigation was conducted. The research started with sintered tracks and finished with multiple layer sintering. The purpose was to find successful conditions and to establish the main problems that need to be overcome. The main achievements of this thesis have been to develop laser power and scan speed sintering maps for a stainless steel powder. 1 he maps have established conditions in which multiple layer blocks can be created, have established strategies to enable large areas to be sintered without warping and show that powder particle size has an important influence on sintering and on the position of the boundaries in the sintering maps. Although this investigation answered some questions, it also raised several more which are presented at the end of this thesis for future work.

Over the last two decades three dimensionally ordered macroporous (3-DOM) materials have turned out to be very promising in many applications ranging from optics, plasmonics, to catalyst scaffolds. The thesis presents a systematic study on formation and characterisation of 3-DOM metals as photonic crystals. Metals are nearly perfect reflectors with low adsorption at microwave or millimetre wavelengths. Meanwhile they generally absorb visible light because of their negative imaginary part of the dielectric constant that could destroy the band gap in the visible though they. Howevers, for noble metals such as gold, silver and copper, considering the Drude-like behaviour, the adsorption will be small enough to achieve a complete photonic band gap for optical or even shorter wavelengths, with silver performing the best. In order to fabricate the 3-DOM metallic nanostructures, template-directed electrochemical deposition has been employed in which, initially a highly ordered film of submircon sized colloidal spheres is deposited on to electronically conducting substrates, for instance, indium-tin oxide (ITO) coated glass substrate, through evaporation-induced self-assembly; and subsequently it is infiltrated with metallic elements electrochemically reduced from corresponding electrolytes; fiannly removal of the colloidal templating film reveals a metallic film comprised of periodically arranged spherical voids. Field Emission Gun Scanning Electron Microscopy (FEGSEM) was used to examine the surface morphology and periodicity of the 3-DOM metallic films. It revealed that highly ordered structures are homogenous and uniform over a large scale for both the original colloidal templates and metallic inverse structures. However for silver electroplated from either silver thiosulfate or silver chlorate bath, voids in the template are fully infiltrated, including both the interstitial spaces between the colloidal spheres and any cracks between film domains, forming a complete solid network over large length scales; for copper the filling factors are strongly dependent on the bath chemistry and in copper sulfate bath isolated macroporous domains can be formed due to those in the cracks will be dissolved back to the solution while those reduced from copper glycerol bath resulted in fully infiltrated structures. Moreover, angle-resolved reflectance spectroscopy has further confirmed the three-dimensional periodicity and indicated the inverse structures have stop band properties in the visible wavelength region, consistent with variation in the effective refractive index of the films. In addition, surface enhanced Raman scattering (SERS) spectroscopy has been used to evaluate applications of the inverse metals as SERS-active substrates. SERS has nearly exclusively been associated with three noble metals copper, silver (by far the most important) and gold. The 3-DOM metallic thin films possess excellent features for SERS detection arising from their long range periodical void geometry, which gives significant enhancement to Raman intensity. Preliminary measurements have demonstrated the 3-DOM metallic structures are well suited for SERS enhancement. Series spectra from different points of each specimen have given reproducible intensities. Variables associated with Raman intensity such as pore size, dye concentration, and film thickness, have been tuned to achieve maximal enhancement for visible and near-IR wavelengths.