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Purpose: Selective laser sintering (SLS) is an essential technology in the field of additive manufacturing. However, SLS technology is limited by the traditional point-laser sintering method and has reached the bottleneck of efficiency improvement. This study aims to develop an image-shaped laser sintering (ISLS) system based on a digital micromirror device (DMD) to address this problem. The ISLS system uses an image-shaped laser light source with a size of 16 mm × 25.6 mm instead of the traditional SLS point-laser light source. Design/methodology/approach: The ISLS system achieves large-area image-shaped sintering of polymer powder materials by moving the laser light source continuously in the x-direction and updating the sintering pattern synchronously, as well as by overlapping the splicing of adjacent sintering areas in the y-direction. A low-cost composite powder suitable for the ISLS system was prepared using polyether sulfone (PES), pinewood and carbon black (CB) powders as raw materials. Large-sized samples were fabricated using composite powder, and the microstructure, dimensional accuracy, geometric deviation, density, mechanical properties and feasible feature sizes were evaluated. Findings: The experimental results demonstrate that the ISLS system is feasible and can print large-sized parts with good dimensional accuracy, acceptable geometric deviations, specific small-scale features and certain density and mechanical properties. Originality/value: This study has achieved the transition from traditional point sintering mode to image-shaped surface sintering mode. It has provided a new approach to enhance the system performance of traditional SLS. [ABSTRACT FROM AUTHOR]

Purpose: Laser sintering of polyamide lattice-based lightweight fairing components for subsequent racetrack testing requires a high quality and a reliable design. Hence, the purpose of this study was to develop a design methodology for such additively manufactured prototypes, considering efficient generation and structural simulation of boundary conformal non-periodic lattices, optimization of production parameters as well as experimental validation. Design/methodology/approach: Multi-curved, sandwich structure-based demonstrators were designed, simulated and experimentally tested with boundary conformal lattice cells. The demonstrator's non-periodic lattice cells were simplified by forward homogenization processes. To represent the stiffness of the top and bottom face sheet, constant isotropic and mapped transversely isotropic simulation approaches were compared. The dimensional accuracy of lattice cells and demonstrators were measured with a gauge caliper and a three-dimensional scanning system. The optimized process parameters for lattice structures were transferred onto a large volume laser sintering system. The stiffness of each finite element analysis was verified by an experimental test setup including a digital image correlation system. Findings: The stiffness prediction of the mapped was superior to the constant approach and underestimated the test results with −6.5%. Using a full scale fairing the applicability of the development process was successfully demonstrated. Originality/value: The design approach elaborated in this research covers aspects from efficient geometry generation over structural simulation to experimental testing of produced parts. This methodology is not only relevant in the context of motor sports but is transferrable for all additively manufactured large scale components featuring a complex lattice sub-structure and is, therefore, relevant across industries. [ABSTRACT FROM AUTHOR]

Purpose: 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. Design/methodology/approach: 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. Findings: 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. Originality/value: 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. [ABSTRACT FROM AUTHOR]

Purpose The purpose of this paper was to verify the possibility of applying differential calculus of incomplete order to describe relaxation of the material obtained using selective laser sintering (SLS) technology.Design/methodology/approach The samples were made using the incremental technology for three print directions. Relaxation tests were conducted. The theoretical curves, which are the solution of the equation describing the five-parameter Maxwell-Wiechert model for derivatives in relation to the total time of complete order and fractional order, were adjusted to the obtained experimental curves.Findings The SLS technology creates new possibilities regarding modelling polymeric elements which might be applied as functional models (products). Therefore, it is necessary to conduct an in-depth study of their properties, including relaxation properties, which is associated with the necessity to use proper mathematical tools to describe those properties. The differential calculus of incomplete order was applied herein to describe the anisotropy of relaxation properties because of the print direction in relation to the relaxation curves adjusted with the five-parameter Maxwell-Wiechert model.Research limitations/implications As a result of the conducted considerations, the authors obtained the dependencies describing the anisotropy of relaxation properties with the use of coefficients alpha and beta, which stand for the derivative order of the differential equation, whereas coefficient kappa stands for the translation coefficient which is an innovative application of this type of mathematical apparatus.Practical implications The developed method might be applied to describe the anisotropy of a broader group of materials manufactured with the use of incremental technologies.Originality/value The application of the differential calculus of incomplete order to describe the anisotropy of the materials manufactured from polyamide powder using the SLS technology is a distinctive feature of this paper. A crucial cognitive element of the conducted research is the fact which confirms that the dynamic viscosity coefficients have the greatest impact on the anisotropy of material properties depending on the print directions. [ABSTRACT FROM AUTHOR]

Purpose The purpose of this paper is to propose and develop PA2200-based composite powder containing 0-15 Wt.% magnesium oxide before directly using it in selective laser sintering (SLS) machine to produce end-use products for low-volume production in the engineering applications with keen focus to meet the functional requirements which rely on material properties.Design/methodology/approach The methodology reported emphasises PA2200-based composite powder containing 0-15 Wt.% magnesium oxide development for SLS process which starts with preparation and characterisation of composite material, thermal and rheological study of composite material to decide optimum process parameters for SLS process machine to get optimal part properties. Further, to verify composite material properties, a conventional casting methodology is used. The composition of composite materials those possessing good properties are further selected for processing in SLS process under optimal processing parameters.Findings The process parameters of SLS machine are material-dependent. The effect of temperature in X-ray diffraction profile is negligible in the case of magnesium oxide reinforced PA2200 composite material. The cyclic heating of material increases melting point temperature, this grounds to modify part bed temperature of material every time before processing on SLS machine to uphold build part properties, as well as material. With the rise in temperature, the Melt flow index and rheological property of materials change. The magnesium oxide reinforced PA2200 composite material has high thermal stability than pure PA2200 material. By the addition of small quantity of magnesium oxide, most of the mechanical property and flammability property improves while elongation at break (percentage) decreases significantly.Practical implications The proposed PA2200-based composite powder containing 0-15 Wt.% magnesium oxide material development system and casting metrology to verify developed material properties will be very useful to develop new composite material for SLS process with use of less material. The developed methodology has proven, especially in the case where non-experts or student need to develop composite material for SLS process according to the property requirement of applications.Originality/value Unlike earlier composite material development methodology, the projected methodology of polymer-based composite material and confirmation of material properties instead of commencing SLS process provides straight forward means for SLS process composite materials development with less use of the material and period of time. [ABSTRACT FROM AUTHOR]

Purpose Orbital fractures are the most commonly encountered midfacial fractures, and usually, the fracture involves the floor and/or the medial wall of the orbit. This paper aims to present an innovative approach for primary and secondary reconstructions of fractured orbital walls through the use of computer-assisted techniques and additive manufacturing.Design/methodology/approach First, through the 3D anatomical modelling, the geometry of the implant is shaped to fill the orbital defect and recover the facial symmetry. Subsequently, starting from the modelled implant, a customised mould is designed taking into account medical and technological requirements.Findings The selective laser sintered mould is able to model and form several kind of prosthetic materials (e.g. titanium meshes and demineralised bone tissue), resulting in customised implants and allowing accurate orbital cavity reconstructions. The case study proved that this procedure, at the same time, reduces the morbidity on the patients, the duration of surgery and the related costs.Originality/value This innovative approach has great potential, as it is an easy and in-office procedure, and it offers several advantages over other existing methods. [ABSTRACT FROM AUTHOR]

Purpose Innovative startups have begun a trend using laser sintering (LS) technology patents expiration, namely, by introducing LS additive manufacturing (AM) machines that can overcome utilization barriers, such as the costliness of machines and productivity limitation. The recent rise of this trend has led the authors to investigate this new class of machines in novel settings, including hub configuration. There are various supply chain configurations to supply spare parts in industrial operations. This paper aims to explore the promise of a production configuration that combines the benefits of centralized production with the flexibility of local manufacturing without the huge costs related to it.Design/methodology/approach This study quantitatively examines the feasibility of different AM-enabled spare parts supply chain configurations. Using cost data extracted from a case study, three scenarios per AM machine technology are modeled and compared.Findings Results suggest that hub production configuration depending on the utilized AM machines can provide economic efficiency and effectiveness to reduce equipment downtime. While previous studies have suggested the need for AM machines with efficiency for single part production for a distributed supply chain, the findings in this research illustrate the positive relationship between multi-part production capability and the feasibility of a hub manufacturing configuration establishment.Originality/value This study explores the promise of a production configuration that combines the benefits of centralized production with the flexibility of local manufacturing without the huge costs related to it. Although the existing body of knowledge contains research on production decentralization, research on various levels of decentralization is lacking. Using a real-world case study, this study aims to compare the feasibility of different levels of decentralization for AM-enabled spare parts supply chains. [ABSTRACT FROM AUTHOR]

Purpose 3D printing is believed to be driving the third industrial revolution. However, a scientometric visualizing of 3D printing research and an exploration its hotspots and emerging trends are lacking. This study aims to promote the theory development of 3D printing, help researchers to determine the research direction and provide a reference for enterprises and government to plan the development of 3D printing industry by a comprehensive understanding of the hotspots and trends of 3D printing.Design/methodology/approach Based on the theory of scientometrics, 2,769 literatures on the 3D printing theme were found in the Web of Science Core Collection’ Science Citation Index Expanded (SCI-EXPANDED) index between 1995-2016. These were analyzed to explore the research hotspots and emerging trends of 3D printing with the software CiteSpaceIII.Findings Hotspots had appeared first in 1993, grew rapidly from 2005 and peaked in 2013; hotspots in the “medical field” appeared earliest and have remained extremely active; hotspots have evolved from “drug”, “printer”, “rapid prototyping” and “3D printing” in the 1990s, through “laser-induced consolidation”, “scaffolds”, “sintering” and “metal matrix composites” in the 2000s, to the current hotspots of “stereolithography”, “laser additive manufacturing”, “medical images”; “3D bioprinting”, “titanium”, “Cstem cell” and “chemical reaction” were the emerging hotspots in recent years; “Commercial operation” and “fusion with emerging technology such as big data” may create future hotspots.Research limitations/implications It is hard to avoid the possibility of missing important research results on 3D printing. The relevant records could be missing if the query phrases for topic search do not appear in records. Besides, to improve the quality of data, this study selected articles and reviews as the research objects, which may also omit some records.Originality/value First, this is the first paper visualizing the hotspots and emerging trends of 3D printing using scientometric tools. Second, not only “burst reference” and “burst keywords” but also “cluster” and “landmark article” are selected as the evaluation factors to judge the hotspots and trends of a domain comprehensively. Third, overall perspective of hotspots and trends of 3D printing is put forward for the first time. [ABSTRACT FROM AUTHOR]

Purpose The purpose of this paper is to investigate the effect of selective laser sintering (SLS) method on morphology and performance of polyamide 12.Design/methodology/approach Crystallization behavior is critical to the properties of semi-crystalline polymers. The crystallization condition of SLS process is much different from others. The morphology of polyamide 12 produced by SLS technology was investigated using scanning electron microscopy, polarized light microscopy, differential scanning calorimetry, X-ray diffraction and wide-angle X-ray diffraction.Findings Too low fill laser power brought about bad fusion of powders, while too high energy input resulted in bad performance due to chain scission of macromolecules. There were three types of crystal in the raw powder material, denoted as overgrowth crystal, ring-banded spherulite and normal spherulite.Originality/value In this work, SLS samples with different sintering parameters, as well as compression molding sample for the purpose of comparison, were made to study the morphology and crystal structure of sintered PA12 in detail. [ABSTRACT FROM AUTHOR]

Purpose Manufacturer specifications for the resolution of an additive manufacturing (AM) machine can be ten times smaller (more optimistic) than the actual size of manufacturable features. Existing methods used to establish a manufacturable design rule-set are conservative piecewise-constant approximations. This paper aims to evaluate the effectiveness of a first-order model for producing improved design rule-sets for feature manufacturability, accounting for process variation.Design/methodology/approach A framework is presented which uses an interpolation method and a statistical model to estimate the minimum size for a wide range of features from a set of iterative experiments.Findings For an SLS process, using this approach improves the accuracy and reliability of minimum feature size estimates for a wider variety of features than assessed by most existing test artifacts.Research limitations/implications More research is needed to provide better interpolation models, broaden applicability and account for additional geometric and process parameters which significantly impact the results. This research focuses on manufacturability and does not address dimensional accuracy of the features produced.Practical implications An application to the design of thin channels in a prosthetic hand shows the utility of the results in a real-world scenario.Originality/value This study is among the first to investigate statistical variation of “pass/fail” features in AM process characterization, propose a means of estimating minimum feature sizes for shapes not directly tested and incorporate a more efficient iterative experimental protocol. [ABSTRACT FROM AUTHOR]

Purpose 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.Design/methodology/approach 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.Findings 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.Originality/value 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. [ABSTRACT FROM AUTHOR]

Purpose The purpose of this paper is to improve the forming efficiency and quality of unequal-width parts fabricated by laser direct metal deposition technology, some experiments were designed.Design/methodology/approach A new method by varying laser spot was adopted to fabricate unequal-width single track using one scanning rather than multi-track overlapping in the way of the inside-beam powder feeding, and the thin-walled parts were fabricated layer by layer. The theoretical model among layer thickness of z-axis, height of single track and the section curve order of single track was established.Findings The top surface unevenness of the thin-walled parts could be compensated automatically within the laser defocusing ranges from −2.5 to −5 mm and from 0.5 to 2.5 mm. The growth rate with the large width/height ratio was more than the small ratio, while the set height of the single track was uniform. The problem of non-uniform growth rate could be solved based on a stepped single-track method. The thin-walled parts with the smooth top surface was fabricated layer by layer which had a continuously variable width from 1 to 3 mm by splicing the laser defocusing range.Practical implications The shapes of the to-be-fabricated parts affect variable laser spot process in practical applications. For example, it will be difficult to apply variable laser spot process on the parts with the hole features.Originality/value This paper provided a guidance for forming unequal-width parts by laser direct metal deposition based on the inside-beam powder feeding. [ABSTRACT FROM AUTHOR]

Purpose This paper aims to provide a review on the process of additive manufacturing of ceramic materials, focusing on partial and full melting of ceramic powder by a high-energy laser beam without the use of binders.Design/methodology/approach Selective laser sintering or melting (SLS/SLM) techniques are first introduced, followed by analysis of results from silica (SiO2), zirconia (ZrO2) and ceramic-reinforced metal matrix composites processed by direct laser sintering and melting.Findings At the current state of technology, it is still a challenge to fabricate dense ceramic components directly using SLS/SLM. Critical challenges encountered during direct laser melting of ceramic will be discussed, including deposition of ceramic powder layer, interaction between laser and powder particles, dynamic melting and consolidation mechanism of the process and the presence of residual stresses in ceramics processed via SLS/SLM.Originality/value Despite the challenges, SLS/SLM still has the potential in fabrication of ceramics. Additional research is needed to understand and establish the optimal interaction between the laser beam and ceramic powder bed for full density part fabrication. Looking into the future, other melting-based techniques for ceramic and composites are presented, along with their potential applications. [ABSTRACT FROM AUTHOR]

Purpose Metal casting industry is in recovery phase after the crisis in 2008; customer demand continues to increase, with 98.6 million metric tons cast in 2011. Traditional ferrous and non-ferrous casting techniques require one shot or permanent moulds which require tooling to produce. Tooling particularly for developmental projects can be costly and take valuable time to produce. Additive manufacturing (AM) has been used to manufacture sand patterns for metal sand casting using laser sintering and sand bonding. This research aims to focus on characterising the sand-bonded process developed by ExOne GmbhH Germany.Design/methodology/approach The approach taken in this research is to evaluate characteristics of parts built in the build volume for dimensional accuracy, tensile and compressive crush strength, density, impact strength and high temperature resistance. These properties are required to compare the 3D sand printing (3DSP) process to direct laser sand sintering (DLSS) and traditional Furan-based casting sand mixtures. The samples were taken from a production machine over a period of 30 days to ensure consistency.Findings The 3DSP process has the capability to manufacture sand patterns to an accuracy of ±0.5 mm or error less than 0.3 per cent; it has also demonstrated the best build position to achieve accurate parts. The research has demonstrated the 3DSP patterns are comparable to traditional methods for important casting material characteristics such as tensile, compression and impact strength. It has been shown that the 3DSP process is capable manufacturing significantly larger parts, with build production rates up to 30 times higher compared to similar parts manufactured via the DLSS process.Research limitations/implications As they has been very few 3DSP machines sold in Europe and particular UK, they has been little research into this new technique, and, therefore, they is a reliance on machine manufactures data for assessment. This research into 3DSP has increased the knowledge of this process significantly.Practical implications This research would be of interest to designers and manufacturing engineers wishing to take advantage of the implications of having new design freedom, tool less manufacturing with short lead times in a wide range of materials using fundamentally tried and tested century’s old casting techniques.Originality/value The research for this paper revealed very little published academic research in this area; therefore, this work will increase the body of knowledge for this niche AM process. [ABSTRACT FROM AUTHOR]

Purpose This paper aims to investigate whether the trabecular architecture found in natural bone can be effectively replicated through the selective laser sintering process of Nylon P2200.Design/methodology/approach Trabecular bone was idealised into a scaled up hexagonal cell proven to replicate the natural structure. The structure was modelled in Solidworks 2013 to form a network of interlinking cells. The specific property analysed was the structure toughness through the measurement of the energy absorbed before sample fracture.Findings It was found that the impact absorption can be increased with the integration of a greater number of trabecular cells producing a finer resolution and not necessarily by increasing the trabecular size. The information gained from this research may be useful in the design of impact and shock absorbing components, with an emphasis on efficient use of material mass.Research limitations/implications Designers and engineers may find biomimetic methods of absorbing shock and impact an efficient alternative consideration in design applications.Practical implications The trabecular architecture should be designed so as to be weaker than the bounding surfaces, ensuring that the individual trabecular experience failure first, maximising their energy absorbing capability through increasing the period of deceleration. The simplest way of doing this is to ensure the rod thickness is less than the bounding material thickness.Originality/value This work documents original testing of both the RP material and consolidated design of samples of idealised bone structures. It builds on previous work in the area and through the results of empirical testing, derives recommendations for further considerations in this area of design and manufacture of biomimetic structures. [ABSTRACT FROM AUTHOR]

Purpose The temperature distribution and history within laser sintered part cakes is an important aspect regarding the process quality and reproducibility of the polymer laser sintering process. This paper aims to an analysis of the temperature history during the build and cooling phase, which is decisive for powder ageing effects and the development of part quality characteristics.Design/methodology/approach A measurement system for three-dimensional in-process temperature measurements is set up and the influence of different parameters on the inner part cake temperature distribution and history is analyzed. In addition, position dependent temperature histories are finally correlated with powder ageing effects.Findings The main parameters influencing the part cake temperature history are figured out. Temperature inhomogeneities on the powder bed surface are detectable within the part cake, but only for a specific time or additional build height. Heat flux through the build frame results in different cooling rates dependent on z height. A combination of process parameters and build job layout results in individual, position-dependent temperature histories. As a consequence, completely different ageing intensities are found within one part cake.Research limitations/implications Temperature measurements are limited to part-free powder cakes so far. To transfer the results to other boundary conditions and machine types, simulation tools have to be developed and validated.Originality/value For the first time, the inner part cake temperature distribution and history have been measured during all build phases and with a high sensor density. The results of this work help to understand the temperature history dependency of powder and part properties and can therefore be used to develop optimized process controls. [ABSTRACT FROM AUTHOR]

Purpose This paper aims to establish a method to verify in real time the quality of a part being built using Selective Laser Sintering (SLS).Design/methodology/approach A SLS build of 30 Nylon 12 tensile bars was done while using an infrared camera to record the thermal history of each bar. The thermal history was then compared to the ultimate tensile strength (UTS) of each bar. In addition, an attempt was made to identify where the fracture of each bar occurred based on its thermal history.Findings Several analysis techniques were used to compare the thermal history of each bar to its UTS. The strongest correlation found was 0.746. In addition, multiple strategies for predicting the break location where used, with the most successful making a correct prediction on 46 per cent of the bars.Originality/value This paper studies the feasibility of in-situ build verification, a technique that if successful would greatly help the further adoption of SLS as a method of manufacturing. [ABSTRACT FROM AUTHOR]

Purpose The purpose of this paper is to provide a better understanding of process parameters that have a significant effect on the shrinkage behaviour of laser-sintered PA 3200GF specimens.Design/methodology/approach A five-factor, three-level and face-centred central composite design was used to collect data, and two methods, namely, response surface methodology (RSM) and artificial neural network (ANN) were used for predicting shrinkage. Sensitivity analysis based on the developed empirical equations has been carried out to determine the most significant parameter, which contributes the most to control shrinkage. In addition, a comparative analysis has also been performed for the results obtained by RSM and ANN.Findings The results revealed that part bed temperature, scan speed and scan spacing are the three dominant parameters, which have a great influence on shrinkage. Strong interactions between laser power-scan spacing, laser power-scan length and scan speed-scan spacing have been observed. Through sensitive analysis, it is observed that shrinkage is more sensitive to the scan speed variations than other four process parameters.Practical implications This study can be used as a guide, and the demonstrated results will provide a good technical database to the different additive manufacturing users of various industries such as automobile, aerospace and medical.Originality/value To the best of the authors’ knowledge, this is the first study to report the shrinkage behaviour of laser-sintered PA 3200GF parts fabricated under different sintering conditions. [ABSTRACT FROM AUTHOR]

Purpose The purpose of this paper is to provide a theoretical foundation for improving the selective laser melting (SLM) surface roughness. To improve the part’s surface quality during SLM process, the upper surface roughness of SLM parts was theoretically studied and the influencing factors were analyzed through experiments.Design/methodology/approach The characteristics of single track were first investigated, and based on the analysis of single track, theoretical value of the upper surface roughness would be calculated. Two groups of cubic sample were fabricated to validate SLM parts’ surface roughness, the Ra and relative density of all the cubic parts was measured, and the difference between theoretical calculation and experiment results was studied. Then, the effect of laser energy density on surface roughness was studied. At last, the SLM part’s surface was improved by laser re-melting method. At the end of this paper, the curved surface roughness was discussed briefly.Findings The SLM upper surface roughness is affected by the width of track, scan space and the thickness of powder layer. Measured surface roughness Ra value was about 50 per cent greater than the theoretical value. The laser energy density has a great influence on the SLM fabrication quality. Different laser energy density corresponds to different fabricating characteristics. This study divided the SLM fabrication into not completely melting zone, balling zone in low energy density, successfully fabricating zone and excessive melting zone. The laser surface re-melting (LSR) process can improve the surface roughness of SLM parts greatly without considering the fabricating time and stress accumulation.Originality/value The upper surface roughness of SLM parts was theoretically studied, and the influencing factors were analyzed together; also, the LSR process was proven to be effective to improve the surface quality. This study provides a theoretical foundation to improve the surface quality of SLM parts to promote the popularization and application of metal additive manufacturing technology. [ABSTRACT FROM AUTHOR]

Purpose The purpose of this paper is to compare different powder metallurgy (PM) processes to produce ceramic parts through additive manufacturing (AM). This creates the potential to rapidly shape ceramic parts with an almost unlimited shape freedom. In this paper, alumina (Al2O3) parts are produced, as Al2O3 is currently the most commonly used ceramic material for technical applications.Design/methodology/approach Variants of the following PM route, with indirect selective laser sintering (indirect SLS) as the AM shaping step, are explored to produce ceramic parts: powder synthesis, indirect SLS, binder removal and furnace sintering and alternative densification steps.Findings Freeform-shaped Al2O3 parts with densities up to approximately 90 per cent are obtained.Research limitations/implications The resulting Al2O3 parts contain inter-agglomerate pores. To produce higher-quality ceramic parts through indirect SLS, these pores should be avoided or eliminated.Originality/value The research is innovative in many ways. First, composite powders are produced using different powder production methods, such as temperature-induced phase separation and dispersion polymerization. Second, four different binder materials are investigated: polyamide (nylon-12), polystyrene, polypropylene and a carnauba wax – low-density polyethylene combination. Further, to produce ceramic parts with increased density, the following densification techniques are investigated as additional steps of the PM process: laser remelting, isostatic pressing and infiltration. [ABSTRACT FROM AUTHOR]

Purpose This paper aims to investigate the curling behaviour of selective laser sintered polyamide/glass bead composites with changes in material compositions, part bed temperature, powder base thickness, laser power and layer cooling time.Design/methodology/approach The Taguchi parameter design method (design of experiments, DOE) and analysis of variance (ANOVA) technique were applied in the investigation to determine the optimal process parameter settings.Findings The results of statistical analysis and ANOVA provided evidence for the effectiveness of filler content and its surface treatment on reducing the amount of curling.Research limitations/implications Warping and curling phenomena is one of several aspects of this work that can be pursued further. The present investigation could be expanded to explore other fillers and interface adhesion using other modifiers. Experiments could be conducted with other complicated geometries, various sizes, different positions and locations to widen the knowledge base of geometric accuracy of selective laser sintering process.Practical implications This experimental work is beneficial for materials development and accuracy characterisation in rapid manufacturing techniques. The experimental techniques adopted are readily transferable to virtually any material system used in rapid manufacturing.Originality/value Although many materials have been developed, there is still a need for research into new materials. This work demonstrates that it is possible to improve the geometric accuracy of selective laser sintered components from glass bead- filled polyamide 12 and achieve near-zero curling by adding rigid multiphase-coated particle to the material system. [ABSTRACT FROM AUTHOR]

Purpose The purpose of this paper is the selection of production parameters in selective laser sintering – SLS for the production of quality products (e.g. good mechanical properties). The manufacturing procedure affects the properties, which is especially significant in additive procedures, as the products are not cheap and the procedure and material need to be optimally selected.Design/methodology/approach The paper presents an analysis of the fabrication parameters in selective laser sintering (SLS) that affect the flexural properties of the finished product. Findings The influence of a new parameter has been found, the overlay ratio, and using the mathematical and scheme method, the selection of parameters for obtaining the optimal flexural properties has been proposed.Originality/value The paper presents a new mathematical model for the calculation of the processing parameters in SLS of polymer products and gives a diagram for the determination of which parameters are the best to use for practical purposes. [ABSTRACT FROM AUTHOR]

Purpose Rapid prototyping (RP) has been given focus during dynamic market conditions, as it largely helps to compress product development time. RP contains the potential to achieve environmentally friendlier operations. However, RP processes are not environmentally friendlier, as the possibilities of toxicological health and environmental risks while handling and disposing of raw material remain unresolved. This study aims to select environmentally friendlier processes without compromising required mechanical properties. Some of the RP processes considered in this study are selective laser sintering (SLS), stereo lithography apparatus (SLA), three-dimensional printing (3DP) and laser engineered net shaping (LENS).Design/methodology/approach A conceptual model comprising 25 criteria (both traditional and environmental) has been developed. An expert team was formed to evaluate the environmental performance of RP processes using the developed conceptual model. Analytic network process–technique for order preference by similarity to an ideal solution-based hybrid methodology has been adopted for this purpose. Further, to overcome ambiguity and subjectivity nature of judgment, fuzzy set concepts have been adopted. Finally, a decision support system has been developed using MATLAB software to mitigate the associated computational difficulty.Findings The detailed analysis of criterion weights revealed that the expert team has assigned higher importance to environmental criteria over traditional criteria. Based on environmental considerations, ranking has been generated as SLA-SLS-3DP-LENS.Research limitations/implications Only point-to-point and discrete fusion-based RP process have been considered in this study to demonstrate the developed conceptual model. Also, expert knowledge has been taken to rate some of the environmental criteria. In the near future, by conducting environmental studies, these criteria can be substituted with real data to improve accuracy of RP process selection.Originality/value Reported studies in RP process selection in literature were conducted considering mainly the various traditional criteria. In this study, the environmental criteria have also been considered along with traditional criteria. This study takes the initiative toward sustainability studies in RP processes. Also, detailed inferences have been derived and the results have been compared with the existing studies and this is the novel contribution of this study. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is to improve the quality of additive manufactured optically translucent parts by investigating the manufacturing issues, analyzing lithophane production criteria and identifying the best translucent material and additive manufacturing (AM) technology. Design/methodology/approach – Figured lithophanes were laser sintered on a 3D Systems SinterStation® HiQ™ with varying layer thickness and plate thickness. Laser sintered (LS) polyamide (PA) 12 blanks were cyanoacrylate infiltrated and polished. Optical properties and performance were compared with the original LS blanks. Lithophanes and blanks were manufactured using 3D systems stereo lithography apparatus (SLA)® Viper ™si2 station, and optical properties and lithophane performance were compared with the LS specimens. Findings – When building in the XY plane, it is optimal to sinter with the minimum layer thickness (0.076 mm) and maximum plate thickness (5 mm). Cyanoacrylate infiltration and polishing assists in reducing the LS PA 12 plate surface roughness, but polishing does not affect the lithophane performance. The best LS candidate should have an absorption coefficient of 0.5/mm using a white light source. Improved resolution but reduced contrast was observed on stereolithography (SL) specimens compared to LS parts. Research limitations/implications – Transmittance experiments were performed on three SL parts which was not sufficient for optical property calculation. Limited literature was found for new material exploration. Originality/value – It is the first effort to study systematically quality improvement issues of LS PA optically translucent parts. A comparison is made of optical performance between parts made using LS and SL. [ABSTRACT FROM AUTHOR]

Purpose – This paper aims to analyze the additive manufacturing orientation effect of laser sintered polyamide 12 (PA 12) optically translucent parts. Design/methodology/approach – Plates with small features, wedges and lithophanes were laser sintered on a SinterStation HiQ™ in different orientations using PA 12. Lithophane performance was assessed using a Picker 240050 X-ray view/light box. All parts were examined using stereomicroscopy to capture the small features. Findings – The quality of the lithophane image was substantially improved by orienting the flat plate side to the incident backlit light. Sintering in the ZX/ZY plane significantly increased the contrast and resolution compared to sintering in the XY plane. The thinnest feature thickness possible in the SinterStation HiQ is in the XY plane 0.13 mm, and it is 0.57 mm when manufacturing in the ZX/ZY plane. Research limitations/implications – The laser spot size and other machine parameters were not changeable, which limited the manufacturing resolution. Oblique, non-orthogonal orientations were not investigated. Originality/value – This is a first effort to investigate the manufacturing orientation effect of laser sintered polyamide optically translucent parts. The manufacturing resolutions on different planes were defined. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is to present Design Rules for additive manufacturing and a method for their development. Design/methodology/approach – First, a process-independent method for the development of Design Rules was worked out. Therefore, geometrical standard elements and attributes that characterize the elements’ shapes have been defined. Next, the standard elements have been manufactured with different attribute values with Laser Sintering, Laser Melting and Fused Deposition Modeling, and their geometrical quality was examined. From the results, Design Rules for additive manufacturing were derived and summarized in a catalogue. Findings – Due to the process independent method, Design Rules were developed that apply for the different considered additive manufacturing technologies equally. These Design Rules are completely function-independent and easily transferable to individual part designs. Research limitations/implications – The developed Design Rules can only apply for the considered boundary conditions. To extend the Design Rules’ validity, their applicability should be proven for other boundary conditions. Practical implications – The developed Design Rules practically support the design of technical parts. Additionally they can be used for training and teaching in the field of “design for additive manufacturing”. Originality/value – The developed Design Rules constitute a first step toward general Design Rules for Additive Manufacturing. Thus, they might form a suitable basis for further scientific approaches, and the Design Rules can be used to set up teaching documentations for lessons and seminars. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is to report selected optical properties of laser sintered polyamide 12 blank plates under different monochromatic and white light conditions and to apply these properties in production of laser sintered lithophanes. Design/methodology/approach – A UNICO 1201E spectrophotometer was used to measure the transmittance of laser sintered polyamide 12 plates as a function of plate thickness. Monochromatic light-emitting diodes were used to assess the wavelength dependence on the transmission and contrast as captured by a SONY DSC-W55 camera. Findings – The transmittance decreased with increasing plate thickness which varied significantly depending on the monochromatic wavelength. Highest transmission was observed using green light (525 nm) and poorest transmission was measured for yellow light (589 nm). Research limitations/implications – There is a limit to the amount of contrast obtained in polyamide lithophanes because the thickness of the plates is limited to less than about 5 mm. Greater thickness results in discernible topology on the lithophane which impairs the quality of the image. Originality/value – Light transmittance of polyamide 12 plates under different lighting conditions is reported and applied to optically defined laser sintered lithophanes. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this study is to show how selective laser sintering (SLS) manufacturing of bioresorbable scaffolds is used for applications in bone tissue engineering. Design/methodology/approach – Polycaprolactone (PCL) scaffolds were computationally designed and then fabricated via SLS for applications in bone and cartilage repair. Findings – Preliminary biocompatibility data were acquired using human mesenchymal stem cells (hMSCs) assuring a satisfactory scaffold colonization by hMSCs. Originality/value – A promising procedure for producing porous scaffolds for the repair of skeletal defects, in tissue engineering applications, was developed. [ABSTRACT FROM AUTHOR]

Purpose - 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. Design/methodology/approach - 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. Findings - 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. Originality/value - 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. [ABSTRACT FROM AUTHOR]

Purpose -- The purpose of this paper is to describe the ageing behaviour of polyamide 12 (PA12) after clinical use. The research is focused on the comparison of the processing methods injection moulding and laser sintering. Design/methodology/approach -- Test specimens are subjected to a cyclic stress of defined bending, cleaning, disinfection and sterilization. The focus of interest in this research is the degradation and reduction of mechanical properties. Findings -- Mechanical and optical changes of the materials after clinical use and hygienic reprocessing are evaluated and discussed. Research limitations/implications -- This article is focused on PA12 and, therefore, enables a very specific statement for the clinical use of PA12. The processing methods could have different impacts depending on the polymer. Originality/value -- With the increasing application of polymers in medical devices, the mechanical properties must be ensured even after long-term clinical use. A systematic research with a realistic and still-defined cyclic stress is shown in this paper. Especially the testing of laser sintered polymers compared to injection moulded material has an important message for future patient-specific products. [ABSTRACT FROM AUTHOR]

Purpose -- The purpose of this paper is to analyze the bulk energy transport processes in the build chamber environment before and during laser sintering (LS) to provide a basis for effective and accurate thermal control for the LS process. This leads to improved mechanical properties and geometrical tolerances for LS products and may be applied to optimize operation cycle times for the LS process. Design/methodology/approach -- Computational models with two levels of complexity were built to explore the heat transfer mechanisms in the LS process. In a one-dimensional model (1D), the powder performed as a semi-infinite solid and heater flux to the powder surface was modeled with a heater control law. A two-dimensional (2D) fluid/solid finite element model of the build chamber and powder bins provided insight into the thermal processes in the build chamber. Findings -- Numerical 1D simulations were verified with measurements from sensors embedded in the build chamber powder bed. Using a 2D model, computed powder surface temperatures during the warm up and build phases were verified with an infrared camera. Convective currents in the build chamber and non-uniformities in the distribution of temperature over the radiant heater surface were found to be substantial contributors to non-uniformities in the powder bed surface temperature. Research limitations/implications -- Limited heat sources were analyzed. No three-dimensional model was built. Assumptions to decrease the part bed temperature difference were not tested. Originality/value -- These simulation and experimental results may be used to enhance thermal control and operation efficiency during the LS process and to improve LS product mechanical properties. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is to report the influence of the peak laser power on laser micro sintering 4-μm nickel powder using Q-switched 1064-nm Nd:YAG laser. Design/methodology/approach – Experimental study has been performed. Nickel powder with grain size of 4 μm has been utilized. A Q-switching duration of 20-25 μs and rate of 20-40 kHz have been used. Findings – The peak power intensity is so high that the metal particles and molten pool are blown away, leading to laser micro sintering not being successfully proceeded. The scanning line obtained by continuous-wave (CW) laser looks like a rod owing to balling effect. Using a suitable peak power intensity, a good-shaped sintering line can be obtained because the plasma can protect the molten metal from oxidation, and improve the wettability of the system. In addition, the plasma flattening effect may also contribute to the form of the good-shaped sintering line in pulsed laser sintering regime. Originality/value – The role of plasma induced by pulsed laser with high peak power intensity has been found during pulsed laser sintering under an ambient environment. [ABSTRACT FROM AUTHOR]

Purpose – This work aims to investigate the direct production of electrical discharge machining (EDM) electrodes by means of the selective laser sintering (SLS) technique using a new non-conventional metal-matrix composite material (TiB2-CuNi). The influence and optimization of the main SLS parameters on the densification behavior and porosity is experimentally studied. EDM experiments are also performed to evaluate the electrodes performance. Design/methodology/approach – The new EDM electrode material used was a powder system composed of TiB2 and CuNi. Making use of a designed systematic experimental methodology, the effects of layer thickness, laser scan speed and scan line spacing were optimized, where aspects such as densification behavior, porosity and surface morphology of the samples were analyzed through microstructural and surface analysis. EDM experiments were conducted under three different regimes in order to observe the electrodes behavior and performance. The results were compared with copper powder electrodes manufactured by SLS and EDMachined under the same conditions. Findings – The experimental results showed that the direct SLS manufacturing of composite electrodes is feasible and promising. The laser scan speed has a high effect on the densification behavior of the samples, while the effect of scan line spacing on the porosity is more visible when the overlapping degree is considered. Surface morphology was not affected by the scan line spacing, whereas balling phenomenon was reported, regardless of the scan line spacing. The EDM results showed that the TiB2-CuNi electrodes had a much superior performance than the copper powder electrodes made by SLS, regardless of the EDM regime applied. Research limitations/implications – Generally, the machine tool itself promotes some restrictions to the SLS process optimization. It is normally attributed to the characteristics of the laser type and the amount of energy that can be delivered to the powder bed. The present investigation could not cover all the optimization potential involved with the studied material due to limitations of the SLS machine tool used. Originality/value – Significant results on the direct SLS manufacturing of a new non-conventional composite material, which has a great technological potential to be used as an EDM electrode material, are presented. Valuable guidelines are given in regard to the SLS optimization of TiB2-CuNi material and its performance as an EDM electrode. This work also provides a systematic methodology designed to be applied to the SLS process to produce EDM electrodes. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is to acquire thermal conductivities of both fresh and preheated polyamide 12 powder under various conditions to provide a basis for effective and accurate control during the laser sintering (LS) process. Design/methodology/approach – A Hot Disk® TPS 500 thermal measurement system using a transient plane source (TPS) technology was employed for thermal conductivity measurements. Polyamide 12 powder was packed at different densities, and different carrier gases were used. Tests were also performed on fully dense laser sintered polyamide 12 to establish a baseline. Findings – Polyamide 12 powder thermal conductivity varies with packing density and temperature, which is approximately one-third bulk form thermal conductivity. Inter-particle bonding is the primary factor influencing polyamide 12 thermal conductivity. Research limitations/implications – Limited ranges of density were tested, and the carrier gas needed carefully control to prevent powder oxidation. Thermal properties obtained were not tested in the LS process. Originality/value – This experimental result could be used to enhance thermal control during the LS process. [ABSTRACT FROM AUTHOR]

Purpose – This paper seeks to present the results of an experiment to investigate the effect of six part orientation (XY, XZ, YX, YZ, ZY, ZX) and a wide range of energy densities on ultimate tensile strength (UTS) and elongation of laser-sintered nylon 12 (PA-12) test specimens. Design/methodology/approach – ASTM Type 1 specimens were built on a DTM Sinterstation 2500+ and tensile tested on an Instron 5569 A. The resulting data were fit to non-linear regression models based on the well-known Weibull growth model to predict each response based on the total energy density used in each trial. Findings – The resulting regression models provide excellent fits with low sum of squared errors and normally distributed residuals. The resulting material properties are highly affected by the energy density and the build orientation. However, once sufficient energy density is applied, properties tend to converge to consistent values. To achieve maximum UTS of approximately 52 MPa, it is recommended that values of energy density above 0.25 W-s per mm3 be used. To achieve maximum elongation of approximately 15-16 percent, it is recommended that values of energy density above 0.40 W-s per mm3 be used when building parts in the XY, XZ, YX, YZ orientations. Parts built in the ZX orientation exhibit lower elongation values at or below 12 percent for even high values of energy density. Originality/value – This paper extends previous work of Starr, Gornet and Usher on the relationship between material properties, part orientation and energy density by proposing the use of the Weibull growth model. Recommendations are provided to assist users in the selection of correct energy density to achieve desirable mechanical properties in each specified orientation. [ABSTRACT FROM AUTHOR]