Gregory John Gibbons

3D printing of porous hydroxyapatite scaffolds intended for use in bone tissue engineering applications.

A systematic characterisation of bone tissue scaffolds fabricated via 3D printing from hydroxyapatite (HA) and poly(vinyl)alcohol (PVOH) composite powders is presented. Flowability of HA:PVOH precursor materials was observed to affect mechanical stability, microstructure and porosity of 3D printed scaffolds. Anisotropic behaviour of constructs and part failure at the boundaries of interlayer bonds was highlighted by compressive strength testing. A trade-off between the ability to facilitate removal of PVOH thermal degradation products during sintering and the compressive strength of green parts was revealed. The ultimate compressive strength of 55% porous green scaffolds printed along the Y-axis and dried in a vacuum oven for 6h was 0.88 ± 0.02 MPa. Critically, the pores of 3D printed constructs could be user designed, ensuring bulk interconnectivity, and the imperfect packing of powder particles created an inherent surface roughness and non-designed porosity within the scaffold. These features are considered promising since they are known to facilitate osteoconduction and osteointegration in-vivo. Characterisation techniques utilised in this study include two funnel flow tests, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), compressive strength testing and computed tomography (CT).

3D Printing of cement composites

Abstract Abstract The aims of this study were to investigate the feasibility of generating three-dimensional (3D) structures directly in rapid hardening Portland cement (RHPC) using 3D printing (3DP) technology. 3DP is an additive layer manufacturing (ALM) process that generates parts directly from CAD in a layer-wise manner. Three-dimensional structures were successfully printed using a polyvinylalcohol/RHPC ratio of 3:97 w/w, with print resolutions of better than 1 mm. The test components demonstrated the manufacture of features, including off-axis holes, overhangs/undercuts, etc. that would not be manufacturable using simple mould tools. Samples hardened by 1 day post-build immersion in water at RT offered modulus of rupture (MOR) values of up to 0·8±0·1 MPa, and, after 26 days immersion in water at RT, offered MOR values of 2·2±0·2 MPa, similar to bassanite based materials more typically used in 3DP (1-3 MPa). Post-curing by water immersion restructured the structure, removing the layering typical of ALM processes, and infilling porosity.

Modelling of weld-bead geometry and hardness profile in laser welding of plain carbon steel using neural networks and genetic algorithms

An attempt was made to predict weld-bead geometry and its cross-sectional micro-hardness profile produced by laser welding of plain carbon steel (DC05) for a given set of process parameters. Welding was done using ytterbium fibre laser by considering laser power, weld speed and distance of the focal point from the sample surface as the input parameters. Microscopy was used to measure the weld dimensions. Micro-indentation was made to measure the corresponding Vickers’ hardness along the horizontal cross section. Two different models were developed. The first model had mean hardness and weld-bead geometry represented by four geometrical dimensions of the weld (that is, top width, depth, mid-width and heat-affected-zone width at mid-depth) as the modelling outputs. The second model had the hardness profile plot interpolation parameters as the modelling outputs. Two different designs of neural networks were used for process-based modelling, namely counter-propagation neural network (CPNN) and feed-forward back-propagation neural network (BPNN), and their prediction capabilities were compared. For the feed-forward neural network, a genetic algorithm was later applied to enhance the prediction accuracy by altering its topology. Back-propagation was implemented using 12 different training algorithms. Mean generalisation error was used to compare the modelling accuracy of the neural networks.

Direct tool steel injection mould inserts through the Arcam EBM free‐form fabrication process

Purpose – The aim of this study is to demonstrate the benefit of design flexibility afforded by the Arcam free‐form fabrication process in the direct manufacture of injection mould inserts with complex cooling channel configurations and the process efficiency and quality gains achieved through using such inserts.Design/methodology/approach – The manufacturing process of a flood cooled injection mould insert using the Arcam EBM S12 layered manufacturing process is presented. The insert is then evaluated against two other inserts (one un‐cooled and one traditionally baffle cooled (BC)) in the manufacture of test components, with the temperature of the insert and components recorded. The process conditions were adjusted (reduced cooling time) to increase the core and component temperatures to identify the operational limits of the inserts. Thermal imaging was employed to visualize the thermal distribution within the BC and flood cooled (FC) inserts.Findings – The cooling efficiency of the FC insert was found...

Virtual relighting of a Roman statue head from Herculaneum: a case study

High-fidelity computer graphics offer the possibility for archaeologists to put excavated cultural heritage artefacts virtually back into their original setting and illumination conditions. This enables hypotheses about the perception of objects and their environments to be investigated in a safe and controlled manner. This paper presents a case study of the pipeline for the acquisition, modelling, rapid prototyping and virtual relighting of a Roman statue head preserved at Herculaneum in Italy. The statue head was excavated in 2006, after having been buried during the eruption of Mount Vesuvius in AD79.

Rapid laminated die‐cast tooling

This paper details the development of a rapid tooling manufacturing route for the gravity and high‐pressure die‐casting industries, resulting from an EPSRC funded collaborative research project between the Universities of Warwick, Loughborough and DeMontfort, with industrial support from, amongst others, MG Rover, TRW Automotive, Sulzer Metco UK Ltd and Kemlows Diecasting Products Ltd. The developed process offers the rapid generation of mould tools from laser‐cut laminated sheets of H13 steel, bolted or brazed together and finish machined. The paper discusses the down‐selection of materials, bonding methods and machining methods, the effect of conformal cooling channels on process efficiency, and the evaluation of a number of test tools developed for the industrial partners. The paper also demonstrates the cost and time advantages (up to 50 and 54 per cent, respectively) of the tooling route compared to traditional fabrication methods.

Analysis of cooling channels performance

The die casting industry is under increasing pressure to improve production rates to enable greater productivity. Employing conformal cooling channels could potentially improve a die performance through the reduction of solidification times. The paper reviews simulated solidification results from a traditional cooling channel design and a conformal cooling channel design. The paper continues by describing the construction of bonded laminate insert with integrated cooling channels. Casting trials were conducted using the inserts to validate the simulated results. Work to date has demonstrated the ability to manufacture laminate inserts quickly, the accuracy of finite element analysis and the importance of designing conformal cooling channels.

Metal spray tooling for composite forming

Thermal spraying methods have been mooted as a method of manufacturing tooling for many years and yet they have not made a significant in-road into this market. Generally, recent metal spraying research has focussed on the manufacture of small, high-pressure tools (for example, for automotive injection moulding tools). However, the metal spray process really lends itself to the manufacture of large tooling where it can compete more effectively against alternatives such as machining. The 3-year, £ 750k, IMI Spray Mould Programme, funded jointly by EPSRC (IMI) and the industrial partners: Airbus, BAE SYSTEMS, Bombardier Aerospace Shorts, A.T. Poeton, Rover Group, and Sulzer Metco, commenced in June 1997. The aim of this research is to develop a method of manufacturing tooling for composite aerospace components, particularly large primary structures over 15 m in length. This paper will present the results of this research programme, including technical data comparing both the technical and economic advantages of this novel approach to tool construction.

Down-selection and optimization of thermal-sprayed coatings for aluminum mould tool protection and upgrade

This article details the down-selection procedure for thermally sprayed coatings for aluminum injection mould tooling. A down-selection metric was used to rank a wide range of coatings. A range of high-velocity oxyfuel (HVOF) and atmospheric plasma spray (APS) systems was used to identify the optimal coating-process-system combinations. Three coatings were identified as suitable for further study; two CrC NiCr materials and one Fe Ni Cr alloy. No APS-deposited coatings were suitable for the intended application due to poor substrate adhesion (SA) and very high surface roughness (SR). The DJ2700 deposited coating properties were inferior to the coatings deposited using other HVOF systems and thus a Taguchi L18 five parameter, three-level optimization was used to optimize SA of CRC-1 and FE-1. Significant mean increases in bond strength were achieved (147±30% for FE-1 [58±4 MPa] and 12±1% for CRC-1 [67±5 MPa]). An analysis of variance (ANOVA) indicated that the coating bond strengths were primarily dependent on powder flow rate and propane gas flow rate, and also secondarily dependent on spray distance. The optimal deposition parameters identified were: (CRC-1/FE-1) O2 264/264 standard liters per minute (SLPM); C3H8 62/73 SLPM; air 332/311 SLPM; feed rate 30/28 g/min; and spray distance 150/206 mm.

Additive manufacturing under pressure

Purpose – This paper aims to investigate the effects on material properties of layer-by-layer application of pressure during fabrication of polymeric parts by additive manufacturing (AM). Although AM, also known popularly as 3D printing, has set a new standard for ease of use and minimal restraint on geometric complexity, the mechanical part properties do not generally compare with conventional manufacturing processes. Contrary to other types of polymer processing, AM systems do not normally use (in-process) pressure during part consolidation. Design/methodology/approach – Tensile specimens were produced in Somos 201 using conventional laser sintering (LS) and selective laser printing (SLP) – a process under development in the UK, which incorporates the use of pressure to assist layer consolidation. Findings – Mechanical testing demonstrated the potential to additively manufacture parts with significantly improved microstructure and mechanical properties which match or exceed conventional processing. For ...