N. P. Lavery

Powder Bed Layer Characteristics: The Overseen First-Order Process Input

Powder Bed Additive Manufacturing offers unique advantages in terms of manufacturing cost, lot size, and product complexity compared to traditional processes such as casting, where a minimum lot size is mandatory to achieve economic competitiveness. Many studies—both experimental and numerical—are dedicated to the analysis of how process parameters such as heat source power, scan speed, and scan strategy affect the final material properties. Apart from the general urge to increase the build rate using thicker powder layers, the coating process and how the powder is distributed on the processing table has received very little attention to date. This paper focuses on the first step of every powder bed build process: Coating the process table. A numerical study is performed to investigate how powder is transferred from the source to the processing table. A solid coating blade is modeled to spread commercial Ti-6Al-4V powder. The resulting powder layer is analyzed statistically to determine the packing density and its variation across the processing table. The results are compared with literature reports using the so-called “rain” models. A parameter study is performed to identify the influence of process table displacement and wiper velocity on the powder distribution. The achieved packing density and how that affects subsequent heat source interaction with the powder bed is also investigated numerically.

The scandium effect in multicomponent alloys

Despite its excellent elemental properties, lightweight nature and good alloying potential, scandium has received relatively little attention in the manufacturing community. The abundance of scandium in the Earths crust is quite high. It is more abundant than silver, cobalt, lead and tin. But, because scandium is so well dispersed in the lithosphere, it is notoriously difficult to extract in commercial quantities – hence low market availability and high cost. Scandium metallurgy is still a largely unexplored field – but progress is being made. This review aims to summarise advances in scandium metallurgical research over the last decade. The use of scandium as a conventional minor addition to alloys, largely in structural applications, is described. Also, more futuristic functional applications are discussed where details of crystal structures and peculiar symmetries are often of major importance. This review also includes data obtained from more obscure sources (especially Russian publications) which are much less accessible to the wider community. It is clear that more fundamental research is required to elevate the status of scandium from a laboratory-based curiosity to a mainstream alloying element. This is largely uncharted territory. There is much to be discovered.

3D solid fin model construction from 2D shapes using non-uniform rational B-spline surfaces

A computer aided design (CAD) tool has been specifically developed for rapid and easy design of solid models for surfboard and sailboard fins. This tool simplifies the lofting of advanced fin cross-sectional foils, in this instance based upon the family of standard airfoil series set by the National Advisory Committee for Aeronautics (NACA), whilst retaining a basic parametric description at each cross-section. This paper describes the way in which non-uniform rational B-spline (NURBS) surfaces are created from 2D profile splines, and are then used to generate 3D geometrical surfaces of the fins, which can be imported directly into commercial software packages for finite element stress analysis (FEA) and computational fluid dynamics (CFD). Pressure distributions, lift and drag forces are determined from a CFD flow analysis for various fins designed with this tool, and the results suggest that the incorporation of advanced foils into surfboard fins could indeed lead to increased performance over fins foiled using current standard techniques. � 2006 Elsevier Ltd. All rights reserved.

Numerical Sensitivity and View Factor Calculation Using the Monte Carlo Method

Abstract In radiative heat transfer simulations, the geometrical view (configuration, form) factor plays a crucial role. Several different methods (deterministic and non-deterministic) such as integration, the Monte Carlo method, and the Hemi-Cube method have been introduced to calculate view factors in recent years. In this article, the Monte Carlo method combined with the finite-element (FE) technique is investigated. Results describing the relationships among different discretization schemes, number of rays used for the view factor calculation, CPU time, accuracy, and two origins of emanating rays are presented. The interesting case where reduced accuracy is obtained with increased refinement of FE mesh is discussed.

Prediction of Long Term Stress Rupture Data for 2124

The standard power law approaches widely used to describe creep and creep fracture behavior have not led to theories capable of predicting long-term data. Similarly, traditional parametric methods for property rationalization also have limited predictive capabilities. In contrast, quantifying the shapes of short-term creep curves using the q methodology introduces several physically-meaningful procedures for creep data rationalization and prediction, which allow straightforward estimation of the 100,000 hour stress rupture values for the aluminum alloy, 2124.

Life cycle assessment of sponge nickel produced by gas atomisation for use in industrial hydrogenation catalysis applications

PurposeThis paper presents a cradle-to-grave comparative life cycle assessment (LCA) of new gas atomised (GA) sponge nickel catalysts and evaluates their performance against the current cast and crush standard currently used in the industrial hydrogenation of butyraldehyde to butanol.MethodsA comparative LCA has been made, accounting for the energy used and emissions throughout the entire life cycle of sponge nickel catalysts—ranging from the upstream production of materials (mainly aluminium and nickel), to the manufacturing, to the operation and finally to the recycling and disposal. The LCA was performed following ISO14040 principles where possible, and subsequently implemented in the software package GaBi 4.3. The CML2001 impact assessment methodology was used, with primary focus on comparing catalysts for equivalent greenhouse gasses generated over their lifetime and their relative global warming potential and secondary focus on acidification potential. This is justified as the lifetime is dominated by energy use in the operational phase, and acidification is dominated by the production of nickel for which existing ISO14040 collected data has been used. A sensitivity analysis was used to provide a number of scenarios and overall environmental performances of the various sponge nickels considered when compared to the existing industrial standard.Results and discussionIt was found that the energy and emissions during the operation phase associated with a given catalyst significantly outweigh the primary production, manufacturing and recycling. Primary production of the nickel (and to a lesser extent molybdenum when used as a dopant) also has a significant environmental impact in terms of acidification potential, but this is offset by operational energy savings over the catalysts’ estimated lifetime and end of life recyclability. Finally, the impact of activity improvement and lifetime duration of sponge nickel catalysts was determined as both total life cycle energy for operational use and as a total life cycle global warming potential.ConclusionsFrom this assessment, the newly developed, higher activity spongy nickel catalysts produced by gas atomisation could have a significantly lower environmental impact than the current industry standard cast and crush method. Given the potential environmental benefits of such catalysts, applications in other processes that require a catalyst should also be investigated.

The three-prong method: a novel assessment of residual stress in laser powder bed fusion

ABSTRACT Residual stress is a major problem for most metal-based laser powder bed fusion (L-PBF) components. Residual stress can be reduced by appropriate build planning and post-process heat treatments; however, it is not always avoidable and can lead to build failures due to distortion and cracking. Accurate measurement of residual stress levels can be difficult due to high equipment set-up costs and long processing times. This paper introduces a simple but novel method of measuring residual stresses via a three-pronged cantilever component, the three-prong method (TPM). The method allows for a quick and easy characterisation of residual stress for a wide range of machine parameters, build strategies and materials. Many different cantilever designs have been used to indicate residual stress within additive manufacturing techniques. All of which share the same shortcoming that they indicate stress in one direction. If the principal component of stress is not aligned with the beam geometry, it will underestimate peak stress values. A novel three-prong design is proposed which covers two dimensions by utilising three adjoined cantilever beams, a configuration which echoes that of hole-drilling where three measurements are used to calculate the stress field around a drilled hole. Each arm of the component resembles a curved bridge-like structure; one end of each bridge is cut away from the base plate leaving the centre intact. Deformation of the beams is then measured using a co-ordinate measurement machine. Stress profiles are then estimated using finite element analysis by meshing the deflected structure and forcing it back to its original shape. In this paper, the new TPM is used to compare the residual stress levels of components built in Ti–6Al–4V with different hatch patterns, powers and exposure times.

A Multiphase CFD Model for the Prediction of Particulate Accumulation in a Laser Powder Bed Fusion Process

Laser Powder Bed Fusion (L-PBF) is a powder based subcategory of metal additive manufacturing. In L-PBF systems an inert gas flow is used to avoid oxidation of the metal alloy powder and components but is also used to remove unwanted by-products produced from the vaporisation of material. By-products produced during in L-PBF can cause attenuation of the laser and re-deposition of unwanted by-products over the processing area which can affect the mechanical properties of as built components. The two main by-products produced in L-PBF are spatter caused from melt pool instabilities and recoil pressure from the metal vapour plume, and particulate condensates. A multiphase computational fluid dynamics model developed in ANSYS Fluent simulates the argon gas flow in a Renishaw AM250 machine validated using hotwire anemometry testing. This model is then coupled with a spatter expulsion discrete phase model supported by high speed imaging analysis and a tertiary phase model for a representative expulsion of particulate condensates is developed.

Computational Modelling of Surfboard Fins for Enhanced Performance

A Computer Aided Design (CAD) tool called Fin Designer has been developed at the University of Wales, Swansea for three-dimensional design of surfboard fins. This tool has been developed as part of a larger project aiming to facilitate design of fins and surfboards for manufacturers with user-friendly software and direct linking into manufacturing processes such as CNC machines and injection molding. This type of tool also provides the basis for in-depth scientific and engineering studies, using engineering software for stress analysis and Computational Fluid Dynamics (CFD), giving deeper insights into potential improvements from design and material modifications. Previous papers (Lavery, Foster, Carswell and Brown 2005; Carswell and Lavery 2006) have dealt with the description of the geometrical models used in the software as well as preliminary computational results made possible by the software. In this paper the emphasis is on the correlation between drag and lift forces for surfboard fins as predicted and measured in a flow tank. Drag and lift forces predicted by the CFD were fed into a specially coded Finite Element Analysis (FEA) to obtain displacements of the fin undergoing these hydrodynamic forces. This paper presents preliminary validation of fluid-solid coupling on the standard benchmark of a cylinder, as well as some results for a single fin. While further verfication of the models are required, the current results appear to suggest that the displacements are of a couple of orders of magnitude smaller than those expected by current fin manufacturers, and hence that fin stiffness remains a strong candidate for fin design improvements.

Case Studying Technology Transfer in an Objective 1 Area.

Two major initiatives are in place in Wales that aim to create a strong and internationally competitive small and medium-sized enterprise (SME) sector. These are the Technology Exploitation Programme (TEP) and the Centres of Excellence for Technology and Industrial Collaboration (CETIC) programme. The Materials Centre of Excellence at the University of Wales Swansea is one of the centres in the CETIC programme with traditionally strong links to the Welsh manufacturing sector. This paper describes the Centres experiences during its first year in the programme as a way of highlighting both the successes and difficulties in the implementation of EU Objective 1 technology transfer initiatives.