A study has been made of the die compaction of metal powders and in particular the problems associated with friction between sliding surfaces have been examined. Friction which results from adhesion or welding, plays an important role in powder consolidation and is greatly influenced by the condition of the surfaces concerned. Attention has been focused upon the compact die interface and the interactions occurring within this region. In particular information has been obtained for friction coefficients between the sliding surfaces and the role of lubricants in affecting these parameters. An assessment has been made of the effect of admixed lubricant level upon the laboratory scale compaction of a reduced iron powder. Ejection forces have been measured and the effects of lubricant content and characteristics evaluated. Die material and surface finish has been shown to be of importance during compaction and ejection. Compact surfaces and strengths have been examined and correlated with the ejection stress data.

The work presented in this thesis is the result of research that aims to enhance the supervisory (level II) control system used at Alcoa Europe FRP and supplied by VAI UK. There are opportunities for improvement in three main areas: improved product shape, especially at low gauges fault diagnosis of product quality, to improve yield optimisation of soaking pits/rolling mill process, to increase throughput and improve efficient use of plant resources. The first part of this thesis focuses on the Expert System developed to augment the existing system for improved supervisory control. The Expert System focuses on utilising human knowledge, whilst the existing system provides the infrastructure for the overall system. The second part of the thesis explains the scheduling system developed to manage the operations of the soaking pits upstream of the rolling mill in order to gain maximum throughput from the overall process and to use the plant resources efficiently.

No description available.

A study was performed to develop new techniques for rolling mill setup and supervisory control. The study was based around three main components, namely a mathematical model of the process, its associated adaptation and an expert system. A novel architecture was developed to integrate the three components into a setup control system, along with some additional functions. The objective of the mill setup system is to determine the optimum mill actuator set points and control targets prior to the rolling of the slab. It is the function of the mill setup and supervisory control system to ensure that the material produced is of primary quality and that a high productivity level is achieved. The novel control architecture incorporates three main components. Firstly, process models are used to predict the states of the rolling process prior to rolling. These models predict the rolling load, motor power and strip temperature, thermal camber of the work rolls, deflection of the mill stack and the profile and shape of the strip. Adaptation ensures that there is a good agreement between measurements and the model predictions. The adaptation is split into two main levels. A Kalman filter is used to predict short term errors in the process model from one pass to the next. Long term variations in the process are tracked using the recursive least squares algorithm. Finally the expert system is used to schedule the mill, diagnose possible faults occurring within the process and to supervise the activities of the other components in the control system. The system is demonstrated in simulation and comparisons are made with and without the expert system control. The results show that there are distinct improvements to be gained with the application of artificial intelligence to an industrial control problem, in this case a hot aluminium rolling mill.

In this PhD thesis the development of laser-based processes for sensing applications is investigated. The manufacture of optical fibre sensors is of particular interest because fibre optics offers advantages in space constraint environments or in environments where electronic sensors fail. Laser micromilling of the transparent and mechanically challenging to machine materials sapphire and fused silica is investigated. An industrial picosecond laser providing 6 ps pulses with the ability to emit at 1030 nm (IR), 515 nm (green) and 343 nm (UV) is used for processing of these materials; providing a maximum laser pulse energy of 25 μJ at UV, 75 μJ at green and 125 μJ in IR. The UV wavelength is identified as the most reliable machining wavelength for these materials with the least amount of cracking and achieving a surface roughness Rq of just 300 nm compared to 1220 nm (green) and 1500 nm (IR) in fused silica. In sapphire the surface roughness is 420 nm using UV , with green it is 500 nm and using IR it is 800 nm. The material removal rates using this laser milling process are larger than with other micromachining techniques, hence it was applied to manufacture cantilever sensors on the end of an optical fibre. The monolithic fibre top sensor is carved out of conventional telecommunications optical fibre. The cantilever is a structure of less than 10 μm thickness, 20 μm width and 125 μm length. Using the Fabry-Perot interferometer method the sensor detects small movements with a resolution better than 15 nm. A technique is developed to correct for laser machining angles and hence generate parallel interferometer faces. An electric arc cleaning process of the laser manufactured cantilever sensors is investigated that reduces the surface roughness to 30 nm. The manufacturing process reduces manufacturing times by a factor of 100. A working sensor is demonstrated in a deflection experiment. Such short pulses are not always required to manufacture the highest resolution sensors. The manufacture of high precision optical encoder scales (pitch 8 μm, depth 200 nm) with two processes (i) ablative removal of a polyimide layer and (ii) a melt reflow process on nickel coated scales is demonstrated. Both processes are using 33 ns laser pulses at 355 nm generating a pulse energy of up to 1 mJ.

Metal spinning is a sheet forming process to produce axisymmetric products, but its commercial operation still depends on a dedicated mandrel which determines the shape of the product, and skilled craftsmen to control the working tool. In Flexible Asymmetric Spinning (FAS) the mandrel is replaced with three numerically controlled internal rollers, thereby removing the setup time and cost associated with producing the dedicated mandrel. However, if FAS could also be automated, the setup time and cost could be reduced further. This thesis focuses on three elements which need to be in place for the automation of FAS: the automation of the internal rollers; compensation for springback; and toolpath design to prevent failure. Typically, automation requires a process model. To automate the internal rollers, a process model which predicts the effect of the internal roller position on the workpiece shape would be required – but as FAS is a novel process, no such models exist. To compensate for springback, a model of workpiece shape is required. To prevent failure, a model of the two modes of failure – wrinkling and tearing – is needed. For offline automation, these should be accurate models – but accurate models of both workpiece shape and failure are too slow to make this feasible. For online automation, fast, approximate models can be used – measurements of the product can be fed back in order to compensate for the model errors. However, a literature review showed that no models exist for workpiece shape or failure which are both fast enough for online use, and detailed enough to give information on how tool actions should be changed. This is why FAS has not yet been automated. In previous work, the internal rollers were positioned through trial-and-error and only a straightwalled cup was successfully produced. In this work, a laser line scanner is installed to measure the workpiece shape online, and one of the internal rollers is positioned at the point where the workpiece just begins to diverge from the target shape. This prevents overlap with the target shape, and allows a greater range of products to be made. Springback is typically prevented in conventional spinning by pressing the material hard against the mandrel. This is not possible in FAS due to the force limits on the internal tools. However, in FAS it is possible to move the working roller inside the target shape to compensate for springback. The laser line scanner is used to measure springback and calibrate a simple elastic cantilever model of springback online. By using this model to calculate how far to move the tool inside the target shape, springback errors are reduced by 75%. Two approaches to toolpath design to avoid failure are investigated: Firstly, a finite horizon control system – where failure is checked for only for a short time into the future – is tentatively demonstrated using a slow but accurate finite element (FE) model, but this is too slow for industrial use. However, with a faster, linear-elastic model, the control system is too conservative and fails to produce the final product. Secondly, an empirical approach is investigated: a series of trials are carried out with a parameterised toolpath. The result is a tentative set of rules for toolpath design which may provide the basis for a future control system. Overall, this thesis makes steps towards the automation of internal rollers, compensation of springback, and design of toolpaths to prevent failure in FAS. With further work to extend the control system developed here to automate all three internal rollers and to verify the robustness of the springback compensation system, any conventional spinning machine could potentially be replaced by an FAS machine – with the toolpath of the working roller designed manually, as it currently is in conventional spinning. Yet the tentative sets of rules on toolpath design also open the door to a potential automatic toolpath generation system, and further work should begin by testing the robustness of these rules with changes in material and geometry. Then, with some likely extensions, they could be embedded into a working control system to fully automate FAS.

No description available.

No description available.

Titanium alloys are used extensively in the aerospace industry due to their high specific strength and excellent corrosion resistance. However, their poor thermal conductivity and high chemical reactivity with tool materials make the machining difficult, especially when grinding. During grinding, the excessive heat generated at the wheel-work piece interface may result in poor surface finisil,1_, a transformed surface layer, excessive plastic deformation, thermallyinduced residual tensile stress, burn and micro-cracking on the ground surface. The poor surface integrity and metallurgical changes of the surface and sub-surface may impair the surface sensitive properties such as fatigue life during service. ln order to overcome the thermal problems when grinding titanium alloys, a new cooling strategy, cryogenic grinding, was studied which involves the supply of liquid nitrogen into the grinding zone using a nozzle jet system. lt was found that cryo-cooling with conventional grinding wheel decreased surface roughness values, burn and plastic deformation of Ti-6Al-4V alloys and produced better a cutting mechanism than when using water-based coolant, especially at higher depths of cut. However, the thermal problems still introduced high residual tensile stress which degraded the fatigue life of ground specimens. Another approach to reducing the grinding temperature was to use a superabrasive wheel (diamond), because of its superior thermal conductivity, the integrity of the ground surface was improved and the fatigue life properties of the specimen were maintained at higher values than for conventional grinding wheels. An ultra stiff machine tool, Tetraform C, was also used to grind Ti-6Al-4V alloys and under selected conditions the ground surface reached a good surface finish and the fatigue properties were also retained at lower depth of cut. An ELID system on the Tetraform C was also investigated. It produced a rougher surface finish in this study. However, it is believed that reducing the wheel loading problem when grinding titanium alloys may contribute to maintaining the fatigue properties.

Grinding is now a well established process utilised for both stock removal and finish applications. Although significant research is performed in this field, grinding still experiences problems with burn and high forces which can lead to poor quality components and damage to equipment. This generally occurs in grinding when the process deviates from its safe working conditions. In milling, chip thickness parameters are utilised to predict and maintain process outputs leading to improved control of the process. This thesis looks to further the knowledge of the relationship between chip thickness and the grinding process outputs to provide an increased predictive and maintenance modelling capability. Machining trials were undertaken using different chip thickness parameters to understand how these affect the process outputs. The chip thickness parameters were maintained at different grinding wheel diameters for a constant productivity process to determine the impact of chip thickness at a constant material removal rate. Additional testing using a modified pin on disc test rig was performed to provide further information on process variables. The different chip thickness parameters provide control of different process outputs in the grinding process. These relationships can be described using contact layer theory and heat flux partitioning. The contact layer is defined as the immediate layer beneath the contact arc at the wheel workpiece interface. The size of the layer governs the force experienced during the process. The rate of contact layer removal directly impacts the net power required from the system. It was also found that the specific grinding energy of a process is more dependent on the productivity of a grinding process rather than the value of chip thickness. Changes in chip thickness at constant material removal rate result in microscale changes in the rate of contact layer removal when compared to changes in process productivity. This is a significant piece of information in relation to specific grinding energy where conventional theory states it is primarily dependent on chip thickness.