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The purpose of this paper is to elucidate the extent to which the mechanisms of polymer melt viscous flow and finish layer powder particle adhesion influence the top surface topographies of laser sintered polyamide (PA12) components.

Laser sintered specimens were manufactured at varying laser parameters in accordance with a full factorial design of experiments. Focus variation microscopy was used to ascertain insight into their top surface heights and peak/valley distributions. Subsequently, regression expressions were generated to model the former with respect to applied laser parameters. Auxiliary experimental analysis was also performed to validate the proposed mechanisms and statistical models.

Within the parameter range tested, this work found the root mean square (S_q) and skewness (S_sk) roughness responses of laser sintered PA12 top surfaces to be inversely related to one another, and both also principally influenced by beam spacing. Furthermore, it was demonstrated that using optimised laser parameters (to promote polymer melt dispersion) and building without finish layers (to avert subsequent powder particle adhesion) reduced the mean S_q roughness of resultant topographies by 30.8% and 47.9% relative to standard laser sintered PA12 top surfaces, respectively.

The scope to which laser sintered PA12 top surfaces can be modified was highlighted.

This research demonstrated the impact the mechanisms of polymer melt viscous flow and finish layer powder particle adhesion have on laser sintered PA12 top surfaces.

The purpose of this paper is to establish the minimum thickness required to provide stab protection in accordance with the United Kingdom Home Office Scientific Development Branch (HOSDB) standards while testing a series of laser sintered (LS) planar specimens using instrumented test apparatus.

Planar test specimens were LS in single-layer thicknesses ranging from 1.00 to 15.00 mm in four material powder categories – DuraForm® virgin, DuraForm 50/50 mix, DuraForm EX® virgin and DuraForm EX 50/50 mix. All specimens were tested using instrumented drop test apparatus and were impacted with established Stanley Tools 1992 trimming blades to the UK HOSDB KR1-E1 stab impact energy level.

The research demonstrated that a minimum single planar specimen thickness of 11.00 mm, manufactured from DuraForm EX 50/50 mix powder, was required to provide protection against the HOSDB KR1-E1 level of stab impact energy. The alternative powder mixes tested within this experiment demonstrated poor levels of stab protection, with virgin powder specimens demonstrating no protection up to 15.00 mm, whereas DuraForm 50/50 mix specimens demonstrating inconsistent performances.

This paper enhances on existing literature surrounding the manufacturing and testing of additive manufacturing (AM) stab-resistant armour by adding further rigour to the testing of AM body armour specimens. In addition, this research establishes key foundation characteristics which could be utilised for the future development of bespoke AM body armour garments.

This study aims to demonstrate for the first time that the cheap, commodity polymer, poly(propylene), can be successfully processed using high speed sintering, and that it can be recycled several times through the process, with little to no detriment to either the polymer itself or the parts obtained. This is significant as a step towards the realisation of high speed sintering as a technology for high-volume manufacturing.

A poly(propylene) powder designed for laser sintering was used to build parts on a high speed sintering machine. The unsintered powder was then collected and reused. Repeating this process allowed creation of seven generations of aged powder. A variety of characterisation techniques were then used to measure polymer, powder and part properties for each generation to discern any effects arising from ageing in the machine.

It was found that poly(propylene) could be used successfully in high speed sintering, albeit with a low build success rate. Increased powder age was found to correlate to an increase in the build success rate, changes in microscopic and bulk powder properties and improvement to the dimensional accuracy of the parts obtained. By contrast, no discernible correlations were seen between powder age and polymer molecular weight, or between powder age and the tensile properties of parts.

This is the first report of the use of poly(propylene) in high speed sintering. It is also first study regarding powder recyclability in high speed sintering, both in general and using poly(propylene) specifically.

The use of laser sintering (LS) in the medical sector has increased dramatically in recent years. With the move towards direct use of these parts in clinical applications, there is a greater need to understand the effects of standard processes on the part properties. The purpose of this study is to determine the effect that steam sterilisation has on the mechanical properties of LS polyamide 12 parts.

The research presented here focusses on the effect of a single steam sterilisation cycle on the mechanical properties of polyamide 12 parts manufactured using LS. The influence of water content on the properties was investigated, with additional drying steps trialled to establish the potential to reverse any changes observed and to determine their root cause.

The results show that steam sterilisation has a significant effect on the mechanical properties of LS polyamide 12 parts, with a 39% reduction in elastic modulus, a 13% decrease in ultimate tensile strength and a 64% increase in the elongation at break. These properties were also all found to correlate with the water content, suggesting that this was the cause of the difference. The original properties of the parts were able to be recovered after oven drying.

These results show that with an additional drying step, LS polyamide 12 parts can be steam sterilised with no effect on the mechanical properties.

This is believed to be the first investigation into the effects of steam sterilisation in isolation on LS polyamide 12 parts, the first instance of drying parts to recover mechanical properties and the first instance of multiple water content measurements being directly linked to the mechanical properties.

X-Ray-computed micro-tomography (micro-CT) is relatively well established in additive manufacturing as a method to determine the porosity and geometry of printed parts and, in some cases, the presence of inclusions or contamination. This paper aims to demonstrate that micro-CT can also be used to quantitatively analyse the homogeneity of micro-composite parts, in this case created using laser sintering (LS).

LS specimens were manufactured in polyamide 12 with and without incorporation of a silver phosphate glass additive in different sizes. The specimens were scanned using micro-CT to characterise both their porosity and the homogeneity of dispersion of the additive throughout the volume.

This work showed that it was possible to use micro-CT to determine information related to both porosity and additive dispersion from the same scan. Analysis of the pores revealed the overall porosity of the printed parts, with linear elastic fracture mechanics used to identify any pores likely to lead to premature failure of the parts. Analysis of the additive was found to be possible above a certain size of particle, with the size distribution used to identify any agglomeration of the silver phosphate glass. The particle positions were also used to determine the complete spatial randomness of the additive as a quantitative measure of the dispersion.

This shows that micro-CT is an effective method of identifying both porosity and additive agglomeration within printed parts, meaning it can be used for quality control of micro-composites and to validate the homogeneity of the polymer/additive mixture prior to printing.

This is believed to be the first instance of micro-CT being used to identify and analyse the distribution of an additive within a laser sintered part.

The 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.

Laser 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.

Results 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.

Further 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.

These results are directly applicable to designers using, or wishing to use, LS to manufacture their products.

Whilst 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.

Selective 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.

SLS 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.

DSC 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.

Further work will correlate the DPM, as measured by the core peak height, with the mechanical properties of the parts produced.

Results 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.

This is believed to be the first time that DSC has been used to indicate the DPM within SLS parts.

The purpose of this paper is to compare four different additive manufacturing (AM) processes to assess their suitability in the context of upper extremity splinting.

This paper describes the design characteristics and subsequent fabrication of six different wrist splints using four different AM processes: laser sintering (LS), fused deposition modelling (FDM), stereolithography (SLA) and polyjet material jetting via Objet Connex. The suitability of each process was then compared against competing designs and processes from traditional splinting. The splints were created using a digital design workflow that combined recognised clinical best practice with design for AM principles.

Research concluded that, based on currently available technology, FDM was considered the least suitable AM process for upper extremity splinting. LS, SLA and material jetting show promise for future applications, but further research and development into AM processes, materials and splint design optimisation is required if the full potential is to be realised.

Unlike previous work that has applied AM processes to replicate traditional splint designs, the splints described are based on a digital design for AM workflow, incorporating novel features and physical properties not previously possible in clinical splinting. The benefits of AM for customised splint fabrication have been summarised. A range of AM processes have also been evaluated for splinting, exposing the limitations of existing technology, demonstrating novel and advantageous design features and opportunities for future research.