Laser melting functionally graded composition of Waspaloy® and zirconia powders.

An approach for fabricating functionally graded specimens of supernickel alloy and ceramic compositions via Selective Laser Melting (SLM) is presented. The focus aimed at using the Functionally Graded Material (FGM) concept to gradually grade powdered compositions of Zirconia within a base material of Waspaloy®. A high power Nd:YAG laser was used to process the material compositions to a high density with gradual but discrete changes between layered compositions. The graded specimens initially consisted of 100% Waspaloy® with subsequent layers containing increased volume compositions of Zirconia (0-10%). Specimens were examined for porosity and microstructure. It was found that specimens contained an average porosity of 0.34% with a gradual change between layers without any major interface defects

Process repeatability and sources of error in indirect SLS of aluminium

Purpose - This paper investigates the accuracy and repeatability of the indirect selective laser sintering of aluminium process. Design/Methodology/Approach – In this paper we characterised the shrinkage of indirect SLS aluminium parts during the various stages of production. Standard scale parts were measured using a Giddings and Lewis co-ordinate measuring machine in both the green and infiltrated condition. Findings – The conducted experiments show that the most accuracy is lost during furnace cycle and that the greatest loss of accuracy occurred in the Z dimensions. Additionally the position of parts within the part bed in both X, Y and Z is shown to influence accuracy, with smaller parts being built closer to the edge of the bed later in the build. These results have been interpreted as being a result of the phenomenon of “Z-growth”. Finally the research shows that the overall accuracy of the indirect selective laser sintering of aluminium process is comparable with many existing processes such as investment casting. Originality/Value – Before any new material can be accepted, there is a need to not only fully characterise the dimensional accuracy attainable, but gain a though understanding of the processes that contribute to the inaccuracies. This paper addresses this need

Analysis of rapid manufacturing—using layer manufacturing processes for production

Rapid prototyping (RP) technologies that have emerged over the last 15 years are all based on the principle of creating three-dimensional geometries directly from computer aided design (CAD) by stacking two-dimensional pro les on top of each other. To date most RP parts are used for prototyping or tooling purposes; however, in future the majority may be produced as end-use products. The term ‘rapid manufacturing’ in this context uses RP technologies as processes for the production of end-use products. This paper reports ndings from a cost analysis that was performed to compare a traditional manufacturing route (injection moulding) with layer manufacturing processes (stereolithography, fused deposition modelling and laser sintering) in terms of the unit cost for parts made in various quantities. The results show that, for some geometries, it is more economical to use layer manufacturing methods than it is to use traditional approaches for production in the thousands

Rapid prototyping for direct manufacture

Advances in rapid prototyping and machining have resulted in reduced lead times for injection moulding tooling. Comparisons between aluminium and stereolithography (SL) tools are made with regard to the ejection forces required to push mouldings from the tools, heat transfer through the tools and the surface roughness of the tools. The results show that ejection forces for both types of tools are increased when a longer cooling time prior to ejection is used. The ejection forces required from a rough aluminium tool are considerably higher than those from a smooth aluminium tool. SL tools do not appear to be subjected to any smoothing as a result of moulding polypropylene parts, this is explained by the fact that the tool’s surface acts in a rubber like manner during part ejection. The rubber like nature of the tool’s surface is as a direct consequence of the low glass transition temperature and low thermal conductivity of the tool material. Further potential benefits of the low thermal properties of the tool are discussed

A comparison between stereolithography and aluminium injection moulding tooling

Advances in rapid prototyping and machining have resulted in reduced lead times for injection moulding tooling. Comparisons between aluminium and stereolithography (SL) tools are made with regard to the ejection forces required to push mouldings from the tools, heat transfer through the tools and the surface roughness of the tools. The results show that ejection forces for both types of tools are increased when a longer cooling time prior to ejection is used. The ejection forces required from a rough aluminium tool are considerably higher than those from a smooth aluminium tool. SL tools do not appear to be subjected to any smoothing as a result of moulding polypropylene parts, this is explained by the fact that the tool’s surface acts in a rubber like manner during part ejection. The rubber like nature of the tool’s surface is as a direct consequence of the low glass transition temperature and low thermal conductivity of the tool material. Further potential benefits of the low thermal properties of the tool are discussed

Predicting stereolithography injection mould tool behaviour using models to predict ejection force and tool strength.

The work reported involved Finite Element Analysis (FEA) modelling of heat transfer in a stereolithography (SL) tool and then performing a series of experiments to measure true heat transfer in the tool. The results from the practical measurement of heat transfer were used to validate and modify the FEA model. The results from the modified FEA model were then used to predict the tensile strength of the tool at various stages after injection of the thermoplastic melt. Previously developed equations to predict ejection forces were used to estimate the ejection forces required to push the moulding from the SL core. During the practical experiments the true ejection forces were measured. The combination of predicted tool strength and ejection forces were intended to be used a basis for to determine whether certain SL tool designs will fail under tension during part ejection. This would help designers and manufacturers to decide whether SL tooling is suitable for a specific application. The initial FEA heat transfer model required some modifications and the measured ejection forces were higher than the predicted values, possible reasons for these discrepancies are given. For any given processing conditions there was an inherent variance in the ejection forces required however longer cooling periods prior to ejection resulted in higher ejection forces. The paper concludes that, due to the variations in required ejection forces, a reliable tool to predict tensile failure will be difficult to produce however improved performance may be gained by adopting processing conditions contrary to those recommended in the current process guidelines

Release characteristics of polymer surface when moulding polyurethane foam

The polyurethane (PU) foam moulding process involves the use of sacrificial release agents (SRAs) that are both costly and harmful to the environment. This research proposes the use of low surface energy, polymer substrates, as a means of eliminating SRAs from the foam moulding process. Previous work identified the major factors affecting the ability of a polymer surface to release a PU foam part as being the surface energy and surface roughness of the substrate, and the proportion of isocyanate in the foam. The research described here has built upon these results and quantified the effects of each factor by using a D optimal design of experiment structure. Crucially it has also been shown that, given the surface energy of a polymer substrate, its roughness and the composition of the foam, it is possible to predict whether or not unaided release should be possible, and a model has been produced in order to allow this prediction for the foams under consideration. This capability will provide the PU foam moulding industry with the possibility of identifying polymeric mould materials, and levels of finishing for these moulds, which have the potential to allow the elimination of SRAs from the production process

Design for environment analyses applied to rapid manufacturing

This paper explores the potential to combine rapid manufacturing (RM) technologies and design for environment (DFE) software with an automotive application. The work focuses on the redesign of a door handle assembly for the Jaguar XJ Saloon. The original 11-piece assembly, comprising eight different materials, was subject to a redesign with an RM technology in mind as the method for final manufacture. In this case the suggested method for manufacture was selective laser sintering (SLS). The design freedoms afforded by the SLS process had a profound effect on the potential to redesign the product. Two different redesigns were proposed, and these, along with the original design, were subjected to analyses of environmental burden and financial profits/costs for end-of-life recycling and reuse using Boothroyd Dewhurst DFE software. The first redesign incorporated the entire assembly as a single prefabricated unit and consequently rendered a DFE analysis impossible. The second redesign was a four-piece assembly retaining three metallic components from the original product and, when subjected to the DFE analysis, showed a significant reduction in environmental burden and cost for disassembly. The surface finish of the SLS parts proved to be inadequate for visual components on a luxury car, but the potential to apply RM for applications with less stringent aesthetic requirements remains

Effect of bed temperature and infra-red lamp power on the mechanical properties of parts produced using high-speed sintering

High-speed sintering is a new, layer-based, manufacturing process, based on printing consecutive cross-sections with a radiation-absorbing material, and exposing to an infra-red lamp, in order to initiate sintering of polymer powder particles in the appropriate profile. Research was carried out to determine the effects of varying process parameters on the mechanical properties of parts produced using this process. Results showed that increasing the temperature of the part bed led to an increase in the mechanical properties of the parts produced, and that increasing the infra-red lamp power had the same effect, but to a lesser degree. It was also found that these increases in process parameters led to a corresponding increase in the hardness of the unsintered powder, which could lead to difficulties with post-process powder removal

Thermal effects on stereolithography tools during injection moulding

In this work the changes to stereolithography (SL) resin mechanical properties during the injection moulding process were evaluated. A multi-impression SL mould was built and used to inject a series of small flat mouldings. The fixed half SL tool insert included recesses to accommodate tensile test specimens. Tensile test specimens made from SL resin were positioned in these recesses and plastic parts were injected. After injecting a predetermined number of mouldings, tensile tests were performed using the tensile test specimens. The results from the tensile tests showed that the thermal cycling encountered during the injection moulding process did not significantly affect the mechanical properties of the resin. Observations indicated that reducing the temperatures encountered in the tool may lead to longer tool life