Purpose
Owing to the operating principle of powder bed fusion processes, selective laser sintering (SLS) requires effective management of the mixture ratio of processed material previously exposed to the high temperatures of processing with new virgin material. Therefore, this paper aims to fully understand the effect that the successive reprocessing has in the powder material and to evaluate its influence on the properties of SLS parts produced at different building orientations.
Design/methodology/approach
Polyamide 12 material with 0%, 30% and 50% of virgin powder and parts produced from them were studied through five consecutive building cycles and their mass, mechanical, thermal and microstructural properties were evaluated. Then, the experimental data was used to validate a theoretical algorithm of prediction capable to define the minimum amount of virgin powder to be added on the processed material to produce parts without significant loss of properties.
Findings
Material degradation during SLS influences the mass and mechanical properties of the parts, exhibiting an exponential decay property loss until 50% of the initial values. The theoretical algorithms of reprocessing proved the appropriateness to use a mixture of 30% of virgin with 70% of processed material for the most common purposes.
Practical implications
This paper validates a methodology to define the minimum amount of virgin material capable to fulfil the operational specifications of SLS parts as a function of the number of building cycles, depending on the requirements of the final application.
Originality/value
The use of theoretical models of prediction allows to describe the degradation effects of SLS materials during the sintering, ensuring the sustainable management of the processed powder and the economic viability of the process.
Abstract. Polycaprolactone scaffolds were produced by electrospinning. Polymeric solutions in a mix of dichloromethane and dimethylformamide were electrospun to form fibers in the sub-micron range. Physical properties of the polycaprolactone solutions were characterized with respect to density, viscosity, conductivity and surface tension. Processing was optimized following Taguchi's methodology to select the set of processing parameters that resulted in producing fibers with the smallest diameters, minimum number of defects and with the narrowest distribution of fiber diameter. Morphology of electrospun fibers was qualitatively and quantitatively analyzed for the different sets of processing parameters. The optimum conditions found to electrospun polycaprolactone were used to process polycaprolactone solutions containing nano-particles of hydroxyapatite or bioactive glass. Bioactivity of nano-composite electrospun membranes in simulated body fluid was analyzed and biological response was tested by assessing proliferation and viability of MT3C3-E1 preosteoblasts cultured on polycaprolactone and its nanocomposite membranes.
This paper examines the effect of export intensity on a firm's capital structure using a sample of 7,676 Portuguese SMEs. Results obtained from a system GMM estimation method show that the leverage ratio is negatively affected by export intensity. We document that firms with more growth opportunities have a higher leverage, while firms that have more profits, higher asset tangibility and face higher business risk have lower debt ratios. Our results also show that the implementation of governmental mechanisms that support export firms' borrowing activities are critical in economies facing a financial crisis.
A three dimensional electro-thermal-fluidic FEM model is introduced in this paper and simulation results are used to design and predict the performance of a polymer based 3-axis thermal accelerometer. The model uses a sequential approach where initially the electro thermal model is simulated and the resulting temperature profile is used as input for a CFD simulation. Simulation results show that the required power to operate the sensor increases with the cross section of the heater and sensor sensitivity depends on the maximum temperature of the heater. Simulations using present sensor geometry show a sensitivity of 0.7°C/g in the X-Y directions and 0.3°C/g in the Z direction for a central heater temperature around 300°C.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.