Meeting high precision requirements of additively manufactured components through hybrid manufacturing

A hybrid approach combining the laser powder bed fusion (LPBF) process and post-processing operations through 5-axis milling was employed to manufacture a Ti6Al4V aerospace component. From the design step, the requirements and needs in all the stages of the Hybrid Additive Manufacturing process were taken into account. A numerical simulation of distortions promoted by residual stresses during the additive process was employed to consider material allowance. The status of the as-built and post-processed component was analysed through scanning and CMM inspection and roughness measurements. The 3D scanned model of the as-built LPBF-ed component was used to understand the distortion behaviour of the component and compared to the numerical simulation. Finally, 5-axis milling operations were conducted in some critical surfaces in order to improve surface quality and dimensional accuracy of the as-built com- ponent. The inspection of the as-built and post-processed component showed the improvement achieved through the proposed hybrid approach. The work aims to provide the baselines needed to enable the metal Hybrid Additive Manufacturing of components with complex geometries where mandatory precision is required by integrating high accuracy machining operations as post-processing technique

Development of calcium phosphate bioceramics with different architectures: Achievements by gelcasting and robocasting technologies

L'abstract è presente nell'allegato / the abstract is in the attachmen

Sol-gel derived hydroxyapatite, fluorhydroxyapatite and fluorapatite coatings for titanium implants

Currently, most titanium implant coatings are made using hydroxyapatite and a plasma-spraying technique. There are however limitations associated with the plasma-spraying process including; poor adherence, high porosity and cost. An alternative - the sol-gel technique offers many potential advantages but is currently lacking research data for this application. Hydroxyapatite (HA), fluorhydroxyapatite (FHA) and fluorapatite (FA) have been synthesised by a sol-gel method. Calcium nitrate and triethyl phosphite were used as precursors under an ethanol-water based solution. Different amounts of ammonium fluoride (NH4F) were incorporated for the preparation of the FHA and FA sol-gels. Optimisation and characterisation of the sol-gels was carried out using, X-ray Diffraction (XRD), High Temperature X-Ray Diffraction (HTXRD), Fourier Transform Infrared Analysis (FTIR) and Differential Thermal Analysis (DTA). Rheology and hydrophilicity of the sol-gels showed that increasing fluoride ion substitution caused an increase in viscosity and contact angle. The dissolution (Ca2+ and PO4 3-rates) rates of the fluoride-substituted powders from the sol-gels were considerably lower than that of HA and all rates could be decreased by increasing the sintering temperature. This suggests the possibility of tailoring the solubility of any coatings made from the sol-gels through fluoride ion substitution and increased sintering temperature. A spin coating protocol has been established for coating the sol-gels onto titanium. Increasing the coating speed decreased the porosity and thickness of the coatings. Bond strengths to titanium were investigated. Fluoride substitution and sintering temperature were shown to be important factors. Cellular proliferation studies revealed that increasing the level of fluoride substitution in the apatite structure significantly increased the biocompatibility of the material. The sol-gel technique may be an alternative to plasma spraying for coating titanium implants. Furthermore it may also be suitable for producing HA, FHA and FA as bone grafting materials

Design and construction of a novel reconfigurable micro manufacturing cell

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.Demands for producing small components are increasing. Such components are usually produced using large-size conventional machining tools. This results in the inadequate usage of resources, including energy, space and time. In the 1990s, the concept of a microfactory was introduced in order to achieve better usage of these resources by scaling down the size of the machine tool itself. Several industries can benefit from implementing such a concept, such as the medical, automotive and electronics industries. A novel architecture for a reconfigurable micro-manufacturing cell (RMC) is presented in this research, aiming at delivering certain manufacturing strategies such as point of use (POU) and cellular manufacturing (CM) as well as several capabilities, including modularity, reconfigurability, mobility and upgradability. Unlike conventional machine tools, the proposed design is capable of providing several machining processes within a small footprint (500 mm2), yet processing parts within a volume up to 100 mm3. In addition, it delivers a rapid structure and process reconfiguration while achieving a micromachining level of accuracy. The approach followed in developing the system is highly iterative with several feedback loops. It was deemed necessary to adopt such an approach to ensure that not only was the design relevant, but also that it progresses the state-of-the-art and takes into account the many considerations in machine design. Following this approach, several design iterations have been developed before reaching a final design that is capable of delivering the required manufacturing qualities and operational performance. A prototype has been built based on the specifications of the selected design iteration, followed by providing a detailed material and components selection process and assembly method before running a performance assessment analysis of the prototype. At this stage, a correlation between the Finite Element Analysis (FEA) model and prototype has been considered, aiming at studying the level of performance of the RMC when optimising the design in the future. Then, based on the data collected during each stage of the design process, an optimisation process was suggested to improve the overall performance of the system, using computer aided design and modelling (CAD/CAM) tools to generate, analyse and optimise the design