Computer aided definition of the printing conditions of parts made by FFF

The growing worldwide use of 3D printing techniques requires the support of scientific research to improve the process and the quality of 3D printed parts. In a previous work, the authors developed a computer code that predicts the temperature evolution and the adhesion at any location of a 3D part produced by Fused Filament Fabrication (FFF). Here, a 3D printed scalpel handle is used as a case study to evaluate the usefulness of the simulation tool in the definition of the printing conditions. Considering a printer with a convection oven, the best built orientation is selected. The results demonstrate the complexity of the heat transfer mechanisms that develop during the deposition stage. For this particular case study, the importance of using a 3D printer fitted with a convection oven is demonstrated, as its positive effect on adhesion cannot be compensated by tuning other process parametersThis work has been partially supported by national funds through FCT – Fundação para a Ciência e Tecnologia through project UIDB/04728/2020. Partial support for this research has been provided by the Search-ON2: Revitalization of HPC infrastructure of Uminho, (NORTE-07-0162-FEDER-000086), co-funded by the North Portugal Regional Operational Programme (ON.2-O Novo Norte), under the National Strategic Reference Framework (NSRF), through the European Regional Development Fund (ERDF), at the University of Minho, Portugal

Studying the cooling stage in fused filament fabrication

Fused Filament Fabrication (FFF) is one of the available techniques that is capable of producing parts by additive manufacturing, i.e., by depositing thin filaments of thermoplastic polymers or composites onto a support as a vertical series of horizontal 2D slices of a 3D part. This chapter approaches FFF from a phenomenological point of view, and then focus on the deposition and cooling stage. A code capable of predicting the evolution of temperature during deposition and until cooling is completed, as well as of the final bonding between filaments is presented. The tool is then used to enlighten the effect of major processing parameters on the quality of parts

The effect of a phase change on the temperature evolution during the deposition stage in fused filament fabrication

Additive Manufacturing Techniques such as Fused Filament Fabrication (FFF) produce 3D parts with complex geometries directly from a computer model without the need of using molds and tools, by gradually depositing material(s), usually in layers. Due to the rapid growth of these techniques, researchers have been increasingly interested in the availability of strategies, models or data that may assist process optimization. In fact, 3D printed parts often exhibit limited mechanical performance, which is usually the result of poor bonding between adjacent filaments. In turn, the latter is influenced by the temperature field history during deposition. This study aims at evaluating the influence of the phase change from the melt to the solid state undergone by semi-crystalline polymers such as Polylactic Acid (PLA), on the heat transfer during the deposition stage. The energy equation considering solidification is solved analytically and then inserted into a MatLab® code to model cooling in FFF. The deposition and cooling of simple geometries is studied first, in order to assess the differences in cooling of amorphous and semi-crystalline polymers. Acrylonitrile Butadiene Styrene (ABS) was taken as representing an amorphous material. Then, the deposition and cooling of a realistic 3D part is investigated, and the influence of the build orientation is discussed.This work has been partially supported by national funds through FCT- Fundação para a Ciência e Tecnologia through project UIDB/04728/2020. Partial support for this research has been provided by the Search-ON2: Revitalization of HPC infrastructure of Uminho, (NORTE-07-0162- FEDER-000086), co-funded by the North Portugal Regional Operational Programme (ON.2-O Novo Norte), under the National Strategic Reference Framework (NSRF), through the European Regional Development Fund (ERDF)

Using matlab to compute heat transfer In free form extrusion

Capítulo 2

Angular momentum conservation and torsional oscillations in the Sun and solar-like stars

The solar torsional oscillations, i.e., the perturbations of the angular velocity of rotation associated with the eleven-year activity cycle, are a manifestation of the interaction among the interior magnetic fields, amplified and modulated by the solar dynamo, and rotation, meridional flow and turbulent thermal transport. Therefore, they can be used, at least in principle, to put constraints on that interaction. Similar phenomena are expected to be observed in solar-like stars and can be modelled to shed light on analogous interactions in different environments. The source of the torsional oscillations is investigated by means of a model for the angular momentum transport within the convection zone. A description of the torsional oscillations is introduced, based on an analytical solution of the angular momentum equation in the mean-field approach. It provides information on the intensity and location of the torques producing the redistribution of the angular momentum within the convection zone of the Sun along the activity cycle. The method can be extended to solar-like stars for which some information on the time-dependence of the differential rotation is becoming available. Illustrative applications to the Sun and solar-like stars are presented. Under the hypothesis that the solar torsional oscillations are due to the mean-field Lorentz force, the mean amplitude of the Maxwell stresses and the phase relationship between poloidal and toroidal field components are obtained. Our preliminary results show the capability of the proposed approach to constrain the amplitude, phase and location of the perturbations leading to the observed torsional oscillations.Comment: 13 pages, 12 figures, accepted by Astronomy & Astrophysic

Predicting the effect of build orientation and process temperatures on the performance of parts made by fused filament fabrication

Purpose: The performance of the parts obtained by fused filament fabrication (FFF) is strongly dependent on the extent of bonding between adjacent filaments developing during the deposition stage. Bonding depends on the properties of the polymer material and is controlled by the temperature of the filaments when they come into contact, as well as by the time required for molecular diffusion. In turn, the temperature of the filaments is influenced by the set of operating conditions being used for printing. This paper aims at predicting the degree of bonding of realistic 3D printed parts, taking into consideration the various contacts arising during its fabrication, and the printing conditions selected. Design/methodology/approach: A computational thermal model of filament cooling and bonding that was previously developed by the authors is extended here, to be able to predict the influence of the build orientation of 3D printed parts on bonding. The quality of a part taken as a case study is then assessed in terms of the degree of bonding, i.e. the percentage of volume exhibiting satisfactory bonding between contiguous filaments. Findings: The complexity of the heat transfer arising from the changes in the thermal boundary conditions during deposition and cooling is well demonstrated for a case study involving a realistic 3D part. Both extrusion and build chamber temperature are major process parameters. Originality/value: The results obtained can be used as practical guidance towards defining printing strategies for 3D printing using FFF. Also, the model developed could be directly applied for the selection of adequate printing conditions.This work is funded by National Funds through FCT – Portuguese Foundation for Science and Technology, References UIDB/ 05256/2020, UIDP/05256/2020 and UIDB/04728/2020. Partial support for this research has been provided by the Search-ON2: Revitalization of HPC infrastructure of UMinho, (NORTE-07–0162- FEDER-000086), co-funded by the North Portugal Regional Operational Programme (ON.2-O Novo Norte), under the National Strategic Reference Framework (NSRF), through the European Regional Development Fund (ERDF), at the University of Minho, Portugal

Monofilament composites of Co-continuous Polyamide12/Poly (Methyl Methacrylate) and carbon nanotubes

Polymer-polymer/carbon nanotube (CNT) composite fibres with a co-continuous morphology were developed, aiming at structural and functional applications. The objective was to produce fibres with electrical conductivity, provided by the incorporation of CNT, maintaining the mechanical properties at a level that allowed typical textile processing. If this goal is achieved, then the fibres may be incorporated into a fabric at specific locations, and be used for sensing purposes. The present work reports the processing of co-continuous bi-polymer CNT composites and the production of mono-filaments with a range of drawing ratios. The composites were processed by melt mixing in a twin-screw extruder. Polyamide 12 (PA12), Poly(methylmetacrylate) (PMMA) and CNT were blended at 78:18:4 weight ratios, incorporated at various positions along the extruder barrel. The CNT remained in the PA12 phase, irrespective of the polymer order of admission in the extruder. In order to achieve electrical conductivity in the CNT/polymer blend a double percolation has to be attained [1], meaning that the polymer bearing the CNT has to be continuously distributed along the fibre, and the CNT dispersed inside that polymer have to form a conductive network. Monofilaments were drawn, their morphology and electrical conductivity were studied. Electrically conductive monofilaments were produced, even at the higher drawing ratios tested.Fundação para a Ciência e a Tecnologia (FCT

Solar rotation rate and its gradients during cycle 23

Available helioseismic data now span almost the entire solar activity cycle 23 making it possible to study solar-cycle related changes of the solar rotation rate in detail. In this paper we study how the solar rotation rate, in particular, the zonal flows change with time. In addition to the zonal flows that show a well known pattern in the solar convection zone, we also study changes in the radial and latitudinal gradients of the rotation rate, particularly in the shear layer that is present in the immediate sub-surface layers of the Sun. In the case of the zonal-flow pattern, we find that the band indicating fast rotating region close to the equator seems to have bifurcated around 2005. Our investigation of the rotation-rate gradients show that the relative variation in the rotation-rate gradients is about 20% or more of their average values, which is much larger than the relative variation in the rotation rate itself. These results can be used to test predictions of various solar dynamo models.Comment: To appear in ApJ. Fig 5 has been corrected in this versio

Energy prices forecasting using GLM

The work described in this article results from a problem proposed by the company EDP - Energy Solutions Operator, in the framework of ESGI 119th, European Study Group with Industry, during July 2016. Markets for electricity have two characteristics: the energy is mainly no-storable and volatile prices at exchanges are issues to take into consideration. These two features, between others, contribute significantly to the risk of a planning process. The aim of the problem is the short term forecast of hourly energy prices. In present work, GLM is considered a useful technique to obtain a predictive model where its predictive power is discussed. The results show that in the GLM framework the season of the year, month or winter/ summer period revealed significant explanatory variables in the different estimated models. The in-sample forecast is promising, conducting to adequate measures of performance.info:eu-repo/semantics/acceptedVersio

Multi-criteria Analysis for the Selection of the Best Energy Efficient Option in Urban Water Systems

AbstractThis paper presents the application of multi-criteria decision analysis to select the best energy efficient option for a water supply system. The case study is a part of the Multi-Municipal Water Supply System (MMWSS) for the Algarve region in Portugal. There is a micro-hydropower plant installed in one of the two water treatment plants. The system has two operating schemes due to the seasonality of tourism: one for the high season from June to September; and the other one for the low season from October to May. The aim of the analysis is to compare the energy efficiency of the system for the two operating schemes and for different demands. Energy audits (i.e., hydraulic energy balance along the pipe system) are carried out for each option (pair operating scheme – demand). Different energy efficiency metrics are calculated and two different multi-criteria analysis methods are used and compared to rank the options. Results obtained are discussed and the main conclusions are presented