No description available.

No description available.

This thesis presents work on the simulation of manufacturing chains, simulation of manufacturing processes (casting, forging, shot-peening and heat treatment) and fatigue life prediction by using the finite element method (FEM). The objectives and the contributions of this thesis consist of development of mathematical algorithms and techniques for mapping and transferring FE data (stresses, strains, displacements, etc.) from macro-to-macro and micro-to-macro FE models among different FE solvers and meshes. All these features have been implemented into a new finite element data exchange system (FEDES). FEDES has been developed to simulate manufacturing chains by using FE techniques. Extensive research has been carried out on the simulation of investment casting processes of aero-engine parts under equiaxed and directional cooling. Methodologies for predicting the component life undergoing low cycle fatigue (LCF) and high cycle fatigue (HCF) have been developed. Life prediction based on the effect of the residual stresses obtained from micro machining and shot-peening processes has been investigated. FEDES has been used to simulate two manufacturing chains where the residual stresses and the distortions after each manufacturing process have been passed to the next process of the chain. Manufacturing chain simulation including casting, forging and heat treatment has been carried out on a simple parallelepiped geometry. A second manufacturing chain simulation has been performed on an aero-engine vane component which includes the following manufacturing processes: metal deposition, welding, heat treatment, machining and shot-peening. An investment casting simulation under equiaxed cooling of the bottom core vane (BCV) component of the aero-engines vane has been performed. The gap formation and the gap conductance have been studied and implemented in the analyses. The main goal is to investigate the residual stresses in the BCV cast with Inconel 718 material. Two FE solvers (ABAQUS and ProCAST) have been used for validation purposes. An investment casting simulation under directional cooling in a Bridgman furnace of a high pressure turbine blade (HPTB) with CMSX-4 material has been carried out. The effect of the withdrawal velocity on the temperature and the residual stresses of the HPTB cast has been investigated.

Reformulation of blended particulate materials has been always a problem for powder industry because formulators have difficulty in measuring, controlling and/or modifying the bulk flow properties of powders. A recently developed powder flow tester (PFT) by The Wolfson Centre for Bulk Solids Handling Technology, University of Greenwich is now available for industry to measure quickly and accurately the flow behaviour of single and blended particulate materials. This new powder flow tester helps to characterise quantitatively the blends which show good flow behaviour in the industrial process lines and define the desirable standards for blends with poor flow behaviour. However, the current process of reformulation is basically a trial and error procedure based on the prior experience of the formulator with other blends reformulated. There is clearly a lack of practical understanding of the links between the particle and bulk scale of powders and how changes in the particle properties and/or blend compositions would affect the flow behaviour of blended powders. The aim of this research work was to develop an “empirical understanding” of the links between the particle properties and bulk flow properties in order to predict the bulk flow properties of blended powders based on changes to the particle properties or blend components. This has been achieved evaluating analytical well-established models found in the literature linking particle and bulk scale for practical purposes in industry, developing new empirical models to predict the flow behaviour of single and blended powders based on the experimental work undertaken in this research and identifying methods or techniques that formulators in industry could use to predict the flow behaviour of their blended powders. The solution provided is a test protocol which in combination with the standard characterisation tests commonly used in industry and the prediction tool called Virtual Powder Blending Laboratory (recently developed by The Wolfson Centre for Bulk Solids Handling Technology using the experimental and modelling work undertaken in this work) will help formulators and process engineers to formulate the composition of blended powders with the desirable flow behaviour in industrial process lines.

Electrochemical machining (ECM) is a non-conventional machining technique capable of machining any conductive substrate, regardless of its physical properties e.g. hardness. ECM became an attractive method due to its ability to machine substrates without creating a defective surface layer. ECM utilises electrolysis; a small gap is maintained between two electrodes whilst a favourable potential is applied between them to remove material from the workpiece. The parameters are adjusted to obtain the desired machining results i.e. surface finish, machining resolution and machining rate. Much work has been conducted for the anodic dissolution of stainless steels and brass but little work outside of these materials is available. This work demonstrates the applicability of ECM for a new range of materials; superconductors and semiconductors, along with the application of ECM for medical needle production and an alteration to the machine set up to anodically dissolve titanium metal at reduced potentials. Through a series of electrochemical techniques, namely polarisation curves, machining potentials were defined for a cuprate superconductor and a semiconductor. These were then demonstrated as suitable settings by completing tests on an electrochemical machine. Hypodermic needles were created on an electrochemical machine and polarisation curves of titanium with the addition of ultrasonic vibrations were used to demonstrate the anodic dissolution of titanium at much reduced potentials.

The University of Manchester,Mohamad Farizal RAJEMI,Doctor of Philosophy,Energy analysis in turning and milling,2010.Energy generation as driven by consumption demand is a key contributor to carbon dioxide emissions and climate change. Hence reducing energy usage is an essential consideration in sustainable manufacturing. In addition, the world is experiencing a higher demand and cost of energy, hence reducing energy usage is an important factor for cost control and economic sustainability. Energy availability and security is now recognised as a key aspect to the socio-political sustainability of nations. Thus, reducing energy demand can be associated with the three; economic, environmental and social sustainability pillars. The manufacturing sector is a key industry that relies on the use of energy in driving value adding manufacturing processes. A widely used process is mechanical machining. This PhD was focussed on an investigation of energy consumption in machining processes and the energy footprints of machined products. A literature review had indicated that despite decades of optimising of machining operations based on cost and productivity, optimising energy use had not received significant attention. In the study a current monitoring device was used to evaluate current requirements and hence power and energy needs for machining processes. The study was done for (i) a range of workpiece materials and (ii) the turning and milling process. This enabled the definition of energy distribution for a machining process and identification of key areas of focus in order to reduce the energy used by a machine tool. The study was then focused on an energy intensive material in terms of machining requirements (titanium alloys) and an in-depth characterisation of the impacts of conventional compared to high speed machining was undertaken. From the study it was clear that a methodology was needed to ensure that energy use can be reduced or optimised. Thus an energy footprint model for a machined component was developed. This model was then used to derive an optimum tool life equation that satisfies the minimum energy criterion. A methodology for selection of optimum cutting conditions was then developed and tested on a component. Thus, the Thesis presents a new and novel model and methodology for selecting optimum cutting conditions for machining, based on minimum energy requirements. The energy savings associated with using such methodologies are quantified and found to be very significant. This work makes a distinct and important contribution to the machining science for reducing the energy and carbon footprints of machined products.

Mechanical micro machining is an emerging material removal process in precision manufacturing industries. There are challenges involved in micro drilling of difficult to cut alloys. These relate to the development of a feasible and reliable manufacturing process given the fragile nature of the micro drill and the poor machinability of difficult to cut materials. Moreover, the established knowledge of macro scale machining may not be directly transferable into micro machining domain. Therefore, mechanical micro machining needs to be adapted to a specific application. Currently, electrical discharge machining (EDM) is an established industrial process for making micro holes in nickel alloys. The mechanical micro drilling process is at present being considered for improved surface integrity, better hole definition and high productivity. Considering the potential of mechanical micro drilling process in nickel based super alloys, the research presented in this thesis focused on developing a novel micro drilling strategy and a process window. Having developed the process window and selected optimum tool geometry, workpiece surface integrity was evaluated at various cutting conditions. Mechanical and microstructural characterization of the modified layers was conducted using electron backscatter diffraction (EBSD), focused ion beam (FIB), backscatter election (BSE), transmission electron microscopy (TEM) and nano-indentation techniques. The mechanisms behind the generation of these modified layers were revealed. The effects of various feedrates, cutting speeds and tool edge radius were analyzed under dry and wet cutting conditions. A new and novel contribution to modified material microstructure analysis was presented in dry and wet drilling conditions. Furthermore, important findings were presented on the tool-chip and tool-workpiece cutting zones. This research provides a comprehensive picture of the surface integrity definition of the micro hole features in drilling nickel based super alloys. Since nickel based super alloys are known for their poor machinability, tool life becomes an important economic variable. For this purpose, tool wear was studied in the micro machining domain. A new tool wear map was developed on a feed-speed plane, identifying low tool wear zones at high productivity. Wear mechanisms were identified which contributed to better understanding of tool-workpiece interactions. A range of different heat resistant and wear resistant coatings were tested which helped identifying the critical material requirements of machining these alloys. Finally, after having developed a complete set of requirements for the mechanical micro drilling process in terms of process window, suitable tool geometry, workpiece surface integrity, tool wear evaluation and selection of suitable coatings for the micro drilling process; the surface integrity produced by mechanical drilling was compared with EDM and laser drilling processes. Mechanical and microstructural character of surface and subsurface layers was assessed. Comparison of surface integrity parameters showed that the mechanical micro drilling process has the potential to benefit industry making micro size holes with better hole definition and surface integrity. This work is an important contribution to industry in that it presents process feasibility assessment and characterization and is regarded by the industrial partners as having achieved Manufacturing Capability Readiness Level (MCRL) 3.

Micro cutting is becoming increasingly important since miniature and micro components/products have become more and more demanded in precision engineering applications and consumer goods in a daily life. Meanwhile, it has not been thoroughly investigated yet. Scientific understanding of the fundamentals in micro cutting mechanics and physics is vital for micro manufacturing of micro or miniature components and products. Consequently, the scientific investigation on micro cutting mechanics is critically needed, particularly on its key fundamental aspects on which a systematic approach and key enabling technologies are developed for micro manufacturing. Therefore, three key fundamental aspects of micro cutting mechanics have been identified for this PhD project and a comprehensive systematic research has been performed through both theoretical and experiment-based investigations. The three aspects of micro cutting mechanics mainly include dynamic stiffness investigation, innovative micro cutting force modelling, and the study on micro cutting heat, temperature and their partitioned distribution. All experiment-based investigations are undertaken on a diamond turning machine test rig supported with a fast tool servo (FTS) using different reconfigured experimental setups. The finite element (FE)-based analysis is conducted to further support the in-depth analysis on the micro cutting phenomena especially the modelling and simulation of micro cutting force and temperature. Accordingly, both micro cutting force modelling and micro cutting temperature are investigated using modelling and simulation supported by well-designed experimental cutting trials and validations. The investigation on dynamic stiffness in the micro cutting system is focused on its effects on the micro cutting process and its control strategies. The burrs formation and machining accuracy are explored in relation with control of the dynamic stiffness. Furthermore, the control algorithm for dynamic stiffness is developed accordingly in order to minimise burrs formation and stabilize the micro cutting accuracy. The micro cutting force modelling is performed based on specific cutting force, i.e. modelling the cutting force at the unit cutting length or area as coined as the amplitude aspect of the proposed cutting force modelling. The cutting force against a dynamically varied cutting time interval is proposed as the spatial aspect of the cutting force formulation. The amplitude aspect can provide the insight into the micro cutting phenomena particularly in relation with the chip formation and size-effects. The spatial aspect, using a on the wavelet transform (WT) technique and standard deviation analysis can render the dynamic behaviour of the micro cutting force, particularly representing the dynamic effects of the cutting process and its correlation with tool wear. The micro cutting temperature is investigated to formulate the scientific understanding of cutting temperature, heat and their partitioned distribution particularly at the tool-workpiece-chip interface zone in ultraprecision and micro cutting using a diamond cutting tool. The contribution to knowledge at this aspect is to represent the partitioned cutting heat in the micro cutting process and their different behaviours compared to the conventional metal cutting. The scientific approach to modelling micro cutting application (MMCA), i.e. based on modelling-simulation combined with experimental validation, is further evaluated and validated to illustrate the overall benefits of this research investigation through micro cutting of single crystal silicon (for ultraprecision machining of large-sized infrared devices). This approach is established in light of combining all the three aspects of the above investigation on micro cutting mechanics. The research results show the approach can lead to industrial scale advantages for ultraprecision and micro cutting but driven by the scientific understanding of micro manufacturing technology. The systematic investigation on dynamic stiffness control, micro cutting force modelling, micro cutting heat and temperature and their integrated approach can contribute well to the future micro cutting applications.

Fibre laser cutting of mild steel using oxygen and nitrogen is widely used in industries throughout the world. An IPG YLR-2000 Ytterbium fibre machine with a maximum power of 2 kW and a wavelength of 1.06 µm is used throughout this research. The effects of oxygen and nitrogen as assist gases on the feature of laser cutting process are different in terms of kerf width, surface roughness, heat affected zone and striation pattern. The kerf width in oxygen laser cutting is wider than that for nitrogen. The striation pattern on oxygen cut edge is smoother than that for the nitrogen cut edge. When using oxygen, the cut edge is covered by a fragile oxide layer while this feature is not seen on the nitrogen cut edge. After laser cutting with oxygen, the cut edge is dross free whilst nitrogen cut edge is drossy. Laser piercing is used to generate a starting point for laser cutting. The pierced hole is normally larger than the kerf width, which means that it cannot lie on the cutline. An experimental programme investigating the piercing process as a function of laser and assist gas parameters is presented. Oxygen and nitrogen were used as assist gases, with pressures ranging from 0.3 to 12 bar. The sizes, geometries and piercing time of the holes produced have been analysed. The pierced hole size decreases with increasing gas pressure and increasing laser power. Oxygen assist gas produced larger diameter holes than nitrogen. A new technique is presented which produces pierced holes no larger than the kerf with and would allow the pierced hole to lie on the cut line of the finished product – allowing better material usage. This uses an inclined jet of nitrogen when piercing prior to oxygen assisted cutting. Specific point energy (SPE) is a concept that has been successfully used in laser welding where SPE and power density determine penetration depth. This analysis allows welding carried out by different laser systems to be directly compared. This work investigates if the SPE concept can be applied to laser cutting. Laser cutting of various thicknesses of mild steel, two different optical set ups and three different delivery fibres with a range of powers and translation speeds is done to gain results for numerous different parameter combinations. It is found that the SPE concept is applicable to laser cutting and the following effects noted: for given material thickness and any given value of SPE, cost is decreased by using a larger beam diameter; for given cut sheet thickness, cutting efficiency increases with SPE; for given value of SPE, cutting efficiency increases as material thickness decreases.

The work in this thesis is concerned with further development of an Intelligent Knowledge-Based System (IKBS) for forging die design. It follows on from initial work carried out at the School of Manufacturing and Mechanical Engineering. The main parts of the original design for the system are a sequence design program (SDP) for two and three dimensional parts, an interface program which can be connected to a finite-element program for metal forming simulation and a Control Module which supervises these two parts and co-ordinates their activities. Of these three modules, only the SDP and the Control Module existed when the current work was started. The purpose of the work reported here is to develop, improve and validate the original system. Among the five different families of components within the original IKBS, Stub Axles have been selected for the current research work. An interface program has been written which can generate a datafile for the available finite-element program (EPFEP3). This interface program inputs one preform stage as the geometry for mesh generation and the corresponding product stage in order to determine the boundary conditions. It also inputs the data within the SDP database for completing the other parts of the datafile. This program is efficient, rapid and user friendly and can easily be extended for the other families of components in the SDP. In the IKBS, when a new component is input to the system, each forming stage of the component should be compared with the same stage of the same family of all the components stored in the database. To do so, the significant processing and geometrical parameters and also their weighting effects should be input to the system. A new experimentally-based approach has been developed to obtain the weighting effects of the significant parameters. The weighting factors obtained are saved in the knowledge-base and have been shown to lead to the correct predictions when data for real forgings was used. The method for obtaining the weighting effects of the significant parameters can be extended to the other families of components within the IKBS. Programs have been written to perform computer-aided reasoning in the IKBS. In particular, recognising and extracting the values of the significant parameters of the operational sequence of a component, creating the IKBS database based on real data and performing the comparison procedure for a new component stage with those stored in the IKBS database.