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The purpose of this research is to determine what tests can be most useful in quality assurance and control when using fused filament fabrication (FFF) 3D printing machines. The quality of the bond between layers is critical for the structural integrity of the fused filament fabricated parts.

Therefore, to determine the influence of process parameters on the quality of parts’ tensile, flexural, notched and un-notched impact, test specimens were fabricated in polylactic acid (PLA) using FFF with different layer thicknesses, fill densities, orientation and print speeds. The mechanical properties were then assessed along with the accuracy and mass of the samples.

It is concluded that a notched impact test gives a measure of interlayer bond strength which can be used across build styles to track machine performance, and that this, together with the mass and dimensions of the impact-test specimens, offers an appropriate set of tests capable of tracking the mechanical properties of parts produced using the FFF technique.

Therefore, this research finding will be of value in benchmarking FFF machines for quality parts fabrications.

This paper aims to develop and then evaluate a novel consolidation and powder transfer mechanism for electrophotographic 3D printing, designed to overcome two longstanding limitations of electrophotographic 3D printing: fringing and a build height limitation.

Analysis of the electric field generated within electrophotographic printing was used to identify the underlying causes of the fringing and build height limitations. A prototype machine was then designed and manufactured to overcome these limitations, and a number of print runs were carried out as proof of concept studies.

The analysis suggested that a machine design which separated the electrostatic powder deposition of the print engine from the layer transfer and consolidation steps is required to overcome fringing and build height limitations. A machine with this build architecture was developed and proof of concept studies showed that the build height and fringing effects were no longer evident.

Electrophotography (EP) was initially seen as a promising technology for 3D printing, largely because the potential for multi-material printing at high speed. As these limitations can now be overcome, there is still potential for EP to deliver a high-speed 3D printing system which can build parts consisting of multiple materials.

The analysis of EP, the new method for the transfer and consolidation of layers and the proof of concept study are all original and provide new information on how EP can be adopted for 3D printing.

Presents procedures which were developed for the manufacture of production tooling using the DTM RapidSteel process, and on the methodology adopted in the generation of the procedures. Accuracy and surface finish, the manufacturability of small features, unsupported features, and mechanical strength have all been investigated, as has the capability of the process for generating conformal cooling channels. An overall tool design and manufacture process is presented, and it is concluded that the DTM RapidSteel process is capable of generating conformally cooled production specification tooling, provided that it is accepted that finishing will be required, and that there are limits on small feature manufacture.

The purpose of this paper is to report on the use of a combination of indirect selective laser sintering (SLS) and machining processes to create injection mould tools, an approach designed to offer the capability to create conformal cooling channels in the core/cavity inserts together with the levels of surface finish and accuracy required to meet typical injection mould tool specifications.

The research has been pursued through three industrial case studies. In each study, existing injection mold inserts have been redesigned to give a conformally cooled tool. These have then been manufactured using indirect SLS, high‐speed machining, electro‐discharge machining and polishing. The inserts have been evaluated in industrial trials to assess their performance in terms of cycle time, energy usage, durability and quality. The insights gained from the three case studies have then been developed into a series of design rules, which may be applied in the development of tooling for new applications.

The results show that significant productivity improvements and energy use reductions in injection moulding are possible through the implementation of conformal cooling, and that the material has sufficient wear resistance to be used in production applications. However, it is recommended that modelling is always used to understand the impact of conformal cooling channels, and manufacture is carefully planned to ensure that the required internal geometry is created.

The paper presents new results on the impact of conformal cooling on the productivity and energy efficiency of injection moulding, and on the durability of the indirect SLS material in injection moulding applications. A novel “cut‐out volume” technique for powder clearing is also presented, along with a set of design rules to support further application of the work.

The purpose of this paper was twofold: first, to determine if rotating bending could be used as an effective way of determining the fatigue behaviour of laser-sintered nylon, and second, to examine whether the fatigue behaviour of laser-sintered PA12 showed any significant anisotropy.

Specimens were measured to obtain dimensional accuracy, density and surface roughness levels. Then, uniaxial tensile and rotating-bending fatigue tests were performed. A purpose-built test-jig has been used to subject hourglass-shaped specimens to reversed bending at two frequencies: 50 and 30 Hz. Additionally, thermal and microstructural analyses were performed to understand the underlying mechanisms of failure.

The experiments suggest PA12 specimens will fail in fatigue following the conventional fatigue mechanisms observed in previous research with ductile polymers. Although high-frequency loading caused a heat build-up in the specimen, temperatures stabilised between 20 and 30°C, suggesting that rotating-bending fatigue at frequencies of up to 50 Hz is a valid way of determining the fatigue behaviour of laser-sintered PA12 specimens. Stresses below 20 MPa led to fatigue lives above 1 million cycles. Some anisotropic behaviour was observed in the fatigue test results, with specimens made orientated with the Z axis showing the lowest fatigue lives on average, but an endurance limit of approximately 15 MPa seems to be common for all specimens regardless of their build orientation.

The observed endurance limit of 15 MPa did not depend significantly on the orientation at which a part was built – meaning that it may be possible to guarantee a service life for a part which does not depend on part orientation within a build. Clearly, good-quality control will also be required to ensure performance, but this has important implications for the design of laser-sintered PA12 parts for realistic service conditions.

To our knowledge, this is the first paper to present rotating-bending fatigue data for laser-sintered PA12 parts, and the first to identify an endurance limit which is independent of part orientation.

The purpose of this paper is to study the effects of particle size distribution, component ratio, particle packing arrangement, and chemical constitution on the laser sintering behaviour of blended hypoeutectic Al‐Si powders.

A range of bimodal and trimodal powder blends were created through mixing Al‐12Si and pure aluminium powder. The powder blends were then processed using selective laser sintering to investigate the effect of alloy composition, powder particle size and bed density on densification and microstructural evolution.

For all of the powder blends the sintered density increases with the specific laser energy input until a saturation level is reached. Beyond this saturation level no further increase in sintered density is obtained for an increase in specific laser energy input. However, the peak density achieved for a given blend varied significantly with the chemical constitution of the alloy, peaking at approximately 9 wt% Si. The tap density of the raw powder mixture (assumed to be representative of bed density) was also a significant factor.

This is the first study to consider the usefulness of silicon as an alloying element in aluminium alloys to be processed by selective laser sintering. In addition the paper outlines the key factors in optimising processing parameters and powder properties in order to attain sound sinterability for direct laser sintered parts.

Though different claims are made in the literature with regard to learning approach differences between mature and non-mature university students, the issue seems to bare detailed study. The purpose of this paper is to report about an investigation of mature and non-mature university students’ learning strategies. The authors examine the relationship between age and learning strategy, and assess to what extent this relationship is mediated by individual and contextual factors.

Using original survey data on 448 university students enroled in Social Sciences programmes in Belgium, this paper examines the relationship between age and learning strategy and assesses to what extent this relationship is mediated by individual and contextual factors.

The results of the multinomial logistic regression show significant differences in learning strategies between both groups of learners. The analyses suggest that mature students are 15.3 percentage points more likely than regular students to adopt a navigator learning strategy. The navigator strategy develops in a non-linear way between the ages 30 and 37. Moreover, only a small part of the learning strategies of mature learners can be explained by mediating factors, with the job involvement playing a particular role.

This study contributes to the body of knowledge concerning the assessment and classification of learning strategies, including a focus on mediators affecting such strategies. The results are confined to only two higher education (HE) institutions. Furthermore, there may be a non-response bias; it is plausible that we miss among the respondents a particular type of mature students such as those that do not like to participate or those that have dropped out of their master’s programme. By means of larger, random samples in future research we should verify this study’s conclusions. This study did not include motivation as a variable. However, it might also explain why mature and non-mature students’ learning approaches differ. Further research could entangle motivational components in relation to learners’ studying approaches.

The research results contribute to our understanding to what extent mature and non-mature students’ learning strategies differ and which mediators are prevalent in explaining these differences. It helps to understand how universities can create a supportive academic environment for mature learners.

The authors found significant differences with regard to learning strategies between mature and non-mature university students. Furthermore, having a professional occupation plays a mediating role in explaining learning strategy differences. The study raises the issue of learner-centred HE, with considerations about differentiated designs of learning environments, programmes and support services targeting students of different ages. By integrating the Assessing the Learning Strategies of Adults instrument, instructional designers can identify learning strategies and take appropriate action to accommodate learners. Additionally, awareness of one’s own learning strategy strengthens mature students’ decision making in self-directed learning environments. In that respect, the authors note also that higher pedagogical flexibility, i.e. more varied educational formats, tracks and study arrangements, ensures adult learners’ access, persistence and retention in HE.

Previous studies suggest that student learning approaches are distinguishable, but did not yet focus on differences between non-mature and mature students. As the authors include graduate students in this study, the focus is on a group which has not been studied previously.

This paper gives a review of the finite element techniques (FE) applied in the analysis and design of machine elements; bolts and screws, belts and chains, springs and dampers, brakes, gears, bearings, gaskets and seals are handled. The range of applications of finite elements on these subjects is extremely wide and cannot be presented in a single paper; therefore the aim of this paper is to give FE researchers/users only an encyclopaedic view of the different possibilities that exist today in the various fields mentioned above. An Appendix included at the end of the paper presents a bibliography on finite element applications in the analysis/design of machine elements for 1977‐1997.