Laser sintering (LS) of polymer materials is a process that has been developed over the last two decades and has been applied in industries ranging from aerospace to sporting goods. However, one of the current major limitations of the process is the restricted range of usable materials. Various material characteristics have been proposed as being important to optimise the laser sintering process, key aspects of which have been combined in this work to develop an understanding of the most crucial requirements for LS process design and materials selection. Using the favourable characteristics of polyamide-12 (the most often used material for laser sintering) as a benchmark, a previously un-sintered thermoplastic elastomer material was identified as being suitable for the LS process, through a combination of information from Differential Scanning Calorimetry (DSC), Hot Stage Microscopy (HSM) and knowledge of viscosity data. Subsequent laser sintering builds confirmed the viability of this new material, and tensile test results were favourable when compared with materials that are currently commercially available, thereby demonstrating the efficacy of the chosen selection process.

PurposeSelective laser‐sintered (SLS) parts are known to include un‐melted regions, where insufficient energy has been input into the powder to fully melt all particles. Previous research has shown the presence of two distinct peaks on a differential scanning calorimetry (DSC), and the purpose of this paper is to demonstrate that these peaks relate to the melted and un‐melted regions of the part.Design/methodology/approachSLS specimens were produced under different build parameters, in order to vary the amount of energy input, and DSC traces produced for each. DSC results were also compared with optical microscopy images to confirm the findings.FindingsDSC analysis of SLS Nylon‐12 parts has shown the presence of two distinct melt peaks. It has been shown that these correspond to the melted and un‐melted regions of the part, and that the amount of energy input in the SLS process affects the degree of melting. It has also been identified, via correlation between DSC charts and optical microscopy images, that the un‐melted, or particle core, peak provides the most adequate indication of the proportion of melting. In order to avoid confusion with the commonly used term “degree of sintering”, which provides only a qualitative description, the new term “degree of particle melt (DPM)” has been defined in order to describe the quantitative variations in the completeness of sintering.Research limitations/implicationsFurther work will correlate the DPM, as measured by the core peak height, with the mechanical properties of the parts produced.Practical implicationsResults have shown that it is possible to identify the level of melting in SLS parts via the use of a DSC chart. Owing to the small size of specimen required for DSC, and the relatively automated DSC procedure, this has the potential for use as quality control in SLS.Originality/valueThis is believed to be the first time that DSC has been used to indicate the DPM within SLS parts.

PurposeThe purpose of this paper is to describe work carried out as part of a £350,000 project aimed at improving understanding of polymer sintering processes. This particular package of research was performed in order to identify the effects of different section thicknesses (and therefore different thermal conditions) in parts produced by laser sintering (LS), on the resultant mechanical properties of these parts.Design/methodology/approachLaser sintered nylon‐12 parts were produced in a range of thicknesses between 2 and 6 mm, and in three different orientations, to identify the effects of each on the tensile properties of these parts.FindingsResults indicated that, at any of the orientations tested, the section thickness had no significant effect on any of the main tensile properties, or on the repeatability of these properties. Crucially, this is in direct contradiction with the trends identified previously in this project, whereby changes in section thickness have been shown to correlate with changes in fracture toughness.Research limitations/implicationsFurther work could investigate a wider range of section thicknesses or geometries, in order to continue building a more complete picture of the effects of geometry on laser sintered part properties.Practical implicationsThese results are directly applicable to designers using, or wishing to use, LS to manufacture their products.Originality/valueWhilst there is a large range of published literature on the effects of processing parameters on mechanical properties of laser sintered parts, and on the resolution and accuracy achievable with these, there is minimal information available on the effects of geometry on mechanical properties. This paper therefore represents a novel addition to the global LS knowledge base.

Infectious diseases (exacerbated by antimicrobial resistance) cause death, loss of quality of life and economic burden globally. Materials with inherent antimicrobial properties offer the potential to reduce the spread of infection through transfer via surfaces or solutions, or to directly reduce microbial numbers in a host if used as implants. Additive Manufacturing (AM) techniques offer shorter supply chains, faster delivery, mass customisation and reduced unit costs, as well as highly complicated part geometries which are potentially harder to clean and sterilise. Here, we present a new approach to introducing antibacterial properties into AM, using Laser Sintering, by combining antimicrobial and base polymer powders prior to processing. We demonstrate that the mechanical properties of the resultant composite parts are similar to standard polymer parts and reveal the mode of the antibacterial activity. We show that antibacterial activity is modulated by the presence of obstructing compounds in different experimental media, which will inform appropriate use cases. We show that the material is not toxic to mammalian cells. This material could be quickly used for commercial products, and our approach could be adopted more generally to add new functionality to Laser Sintered parts. The global Additive Manufacturing (AM) market has grown by an average of 26.9% annually for the last 30 years, with the overall revenue of the industry currently estimated at $9.8 billion, and aerospace, automotive and healthcare being major sectors 1. Parts are produced in a layer-by-layer manner, directly from a Computer-Aided Design (CAD) file. This layer-by-layer approach provides key benefits through removing the need for tooling and increasing the ease with which complex geometries can be produced. However, despite their clear potential, the range of materials that can be used in AM processes is limited compared to more traditional manufacturing techniques, which in turn has restricted the range of applications in which they can be used. Laser Sintering is an AM technology that produces parts by selectively scanning and melting consecutive cross-sections of polymer powder particles. Areas which have not been scanned remain as loose powder throughout the process, acting to support any overhanging areas, which in turn allows the economic production of highly complex part geometries. This geometric capability makes Laser Sintering highly suited to production of complex, optimised, products and devices, or to the production of products and devices personalised to individuals. However, particularly when considering hand-held and/or medical products, increasing geometric complexity can render them difficult and time-consuming to clean effectively, potentially providing increased chance of spread of bacteria. Incorporation of antibacterial properties into the parts themselves could reduce or eliminate this risk, and is the focus of this work. Many antimicrobial products are currently available to purchase, with a growing global market fo...

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