Candice E. Majewski

Degree of particle melt in Nylon‐12 selective laser‐sintered parts

Purpose – 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.Design/methodology/approach – 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.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 im...

Effect of the degree of particle melt on mechanical properties in selective laser-sintered Nylon-12 parts

Selective laser sintering (SLS®, a trademark of 3D systems Inc.) is a manufacturing process which has emerged from numerous other technologies as the leading process considered viable for rapid manufacturing (RM). SLS of polymers has found use in a wide range of industries ranging from aerospace to medicine. The ability to manufacture easily parts that previously have been difficult or impossible to produce, without tooling, has proved invaluable for many applications. A major area of focus within RM is the requirement to produce parts with more repeatable mechanical properties than can currently be achieved. This research has investigated the use of a novel method of interpreting a differential scanning calorimetry curve to indicate the level of melting within semicrystalline selective laser-sintered parts, or the degree of particle melt (DPM). The DPM has been shown firstly to be affected by the amount of energy input into the process whereby, as the energy input increases, the DPM also increases. Results have also shown that, as the DPM increases, the tensile strength and elongation at break also increase, whilst there is no significant effect on the Youngs modulus. These findings will enhance the ability to optimize and predict the properties of the SLS process, an area which is critical when producing end-use parts, particularly when considering demanding applications such as in the aerospace and automotive industries.

Effect of section thickness and build orientation on tensile properties and material characteristics of laser sintered nylon‐12 parts

Purpose – 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.Design/methodology/approach – 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.Findings – 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 wit...

Study into the recyclability of a thermoplastic polyurethane powder for use in laser sintering

Previous studies into the use of polymer powders such as Nylon-12 for laser sintering have shown part property degradation caused by repeated heating and cooling. This research investigated the recyclability of a new thermoplastic polyurethane powder in the laser sintering process. The work has novel value as there has been no previous work on processing this material by laser sintering. A virgin powder sample was retained, along with a sample after each of four laser sintering builds. Each sample’s recyclability was investigated by particle size analysis, differential scanning calorimetry, hot stage microscopy of particle pairs, melt flow index, tensile test sample manufacture and tensile testing. Upon recycling, no significant trend in the elastomer particle size distribution was identified, and thermal properties were unchanged, as shown by differential scanning calorimetry analysis. Hot stage analysis showed that recycling had no clear effect on sintering time. Melt flow index results showed a small increase in flow rate upon recycling, corresponding to a slight drop in viscosity, suggesting reduced chain length. The outcome of tensile tests showed a minor decrease in strength while elongation at break and Young’s modulus showed a negligible decrease. The results have shown the possibility of recycling the thermoplastic polyurethane bed powder several times through the laser sintering process without any significant degradation or reduction in properties.

Effect of infra-red power level on the sintering behaviour in the high speed sintering process

Purpose – To investigate the effects of the infra‐red power level on sintering behaviour in the high speed sintering (HSS) process.Design/methodology/approach – Single‐layer parts were produced using the HSS process, in order to determine the effect of the infra‐red power level on the maximum achievable layer thickness, and the degree of sintering. The parts were examined using both optical microscopy and contact methods.Findings – It was initially expected that an increase in the infra‐red lamp powder might allow an increase in the depth of sintering that could be achieved, as a result of increased thermal transfer through the powder. However, results in fact indicated that there is a maximum layer thickness that can be achieved, as a result of part shrinkage in the z direction. Optical microscopy images have shown that a greater degree of sintering occurs at higher power levels, which would be expected to correspond to an improvement in the mechanical properties of the parts produced. These images also ...

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.

Effect of tool finishing on ejection forces for injection moulded parts made using direct metal laser sintered tools

With the continuing development of Rapid Prototyping technologies, there has been a move into areas of Rapid Tooling. This takes advantage of the shorter lead times and lower costs associated with the production of tooling, particularly for injection moulding. This paper analyses the effectiveness of using direct metal laser sintering to produce injection-moulding tools, in terms of the force required to eject a part from a tool. Different levels of finishing were applied to test tools, and the results show that in some cases the forces required to eject parts from direct metal laser sintered tools were comparable with those from machined tools.

Demonstration of Normal and Abnormal Fetal Brains Using 3D Printing from In Utero MR Imaging Data

SUMMARY: 3D printing is a new manufacturing technology that produces high-fidelity models of complex structures from 3D computer-aided design data. Radiology has been particularly quick to embrace the new technology because of the wide access to 3D datasets. Models have been used extensively to assist orthopedic, neurosurgical, and maxillofacial surgical planning. In this report, we describe methods used for 3D printing of the fetal brain by using data from in utero MR imaging.

A Novel Approach to Personalising the Mechanical Properties of Sprint Footwear (P179)

A novel method for adapting the mechanical properties of sprint shoe sole units is explored. Five different ratios of glass to nylon were mixed and laser sintered to produce standard test samples and sprint shoe sole units. Samples were subjected to standard tensile test procedures and sole units were tested in a purpose built fixture. In-filling nylon-12 with higher ratios of glass increased longitudinal bending stiffness. The mean force in extension over the tested range was 8.9 and 16.0 N for the 0% and 50% glass filled sole units respectively. The mean force in flexion over the tested range was 11.6 and 17.7N for the 0% and 50% glass filled sole units. However, increased stiffness comes at the expense of ductility and mechanical evaluation over the shoes functional range resulted in mechanical failure for the sole units in-filled with 50% glass. Further work on alternative base and infill materials needs to be conducted before the technique is suitable for functional footwear.

Release characteristics of polymer surface when moulding polyurethane foam

Abstract 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.