Repositório Colecção: DEP - ART
https://hdl.handle.net/1822/12002
DEP - ART2024-03-29T09:39:44ZExperimental study of PLA thermal behavior during fused filament fabrication
https://hdl.handle.net/1822/89867
Título: Experimental study of PLA thermal behavior during fused filament fabrication
Autor: Vanaei, Hamid Reza; Shirinbayan, Mohammadali; Costa, Sidonie Fernandes; Duarte, F. M.; Covas, J. A.; Deligant, Michael; Khelladi, Sofiane; Tcharkhtchi, Abbas
Resumo: Fused filament fabrication (FFF) is an additive manufacturing technique that is used to produce prototypes and a gradually more important processing route to obtain final products. Due to the layer-by-layer deposition mechanism involved, bonding between adjacent layers is controlled by the thermal energy of the material being printed, which strongly depends on the temperature development of the filaments during the deposition sequence. This study reports experimental measurements of filament temperature during deposition. These temperature profiles were compared to the predictions made by a previously developed model. The two sets of data showed good agreement, particularly concerning the occurrence of reheating peaks when new filaments are deposited onto previously deposited ones. The developed experimental technique is shown to demonstrate its sensitivity to changing operating conditions, namely platform temperature and deposition velocity. The data generated can be valuable to predict more accurately the bond quality achieved in FFF parts.
<b>Tipo</b>: article2024-03-22T14:10:33ZTransmission laser welding of thermoplastics: influence of welding parameters and rib dimensions on the strength of welded joints
https://hdl.handle.net/1822/89859
Título: Transmission laser welding of thermoplastics: influence of welding parameters and rib dimensions on the strength of welded joints
Autor: Bastos, Lourenço; Alves, Marco; Sousa, Bruno; Vilela, Andreia; Rietter, Luciano; Duarte, F. M.; Carneiro, Filipa; Żmijewska-Rocha, Agnieszka
Resumo: Laser transmission welding of injection moulded thermoplastics is commonly used in industrial applications such as electronic packaging, textiles, biomedical devices, windows, signs, food and medical packaging, visual displays and automotive components due to very precise control of the process parameters, including the amount of energy delivered and its location, which results in high joint quality. In this article, the influence of laser transmission contour welding parameters and geometry of welding rib on joint force is investigated. Velocity with which the laser beam moves on the sample, temperature applied, clamp force, laser beam size and number of laser passes were studied for various dimensions of the rib with rectangular and triangular cross section. Samples of different thermoplastic materials, PMMA and PC/ABS, were produced and then joined by transmission laser welding and after that were subjected to tensile tests, in order to measure strength of the joint between the plastic parts. Initially, optimal welding conditions were found for each studied rib and their influence on the force of the joint was analysed. Afterwards, a comparison between the best results obtained for each rib was performed, in order to define the dimensions of the rib that result in the highest joint force. It was observed that samples with triangular ribs achieved higher joint strength. For both studied geometries of rib cross section, an increase of the width of the ribs improves the joint strength, while an increase of the height worsens it.
<b>Tipo</b>: article2024-03-22T12:04:36ZEffect of polymer type on the properties of polypropylene composites with high loads of spent coffee grounds
https://hdl.handle.net/1822/89852
Título: Effect of polymer type on the properties of polypropylene composites with high loads of spent coffee grounds
Autor: Marques, Mariana; Gonçalves, Luís Filipe Fernandes Ferreira; Martins, Carla I.; Vale, Mário; Duarte, F. M.
Resumo: The main focus of this work is to study the processability and characteristics of highly loaded spent coffee grounds (SCG) thermoplastic polymer composites, for sustainable applications. SCG powder was characterized in terms of size distribution, moisture, morphology and thermal stability. Polymer/SCG composites were prepared by extrusion compounding. Polypropylene (PP) homopolymer and copolymer were used as the polymeric matrix. Upon compounding by extrusion composites were injection moulded and characterized for its physical, morphological and mechanical properties in order to determine the effect of polymer type and filler content. Morphological characteristics of the composites were investigated using optical microscopy and SEM analysis. The results for PP homopolymer showed little deterioration of the mechanical properties when using the highest SCG load. In the case of PP homopolymer, the greatest variations occurred when increasing from 0 to 20 %. With higher SCG loads, the measured properties changed little. PP copolymer showed a more continuous pattern of properties decay with increasing SCG load, especially for tensile strength, elongation at break and impact strength. Regarding PP copolymer, with maximum SCG load, the tensile strength decreased from 26.8 GPa (neat PP) to 10.8 GPa, the elongation at break showed a drop of more than 95 %, while the Young's modulus increased from 800 MPa to 1160 MPa. This research work has shown that SCG can be used as fillers in the preparation of environmentally friendly composites with SCG load up to 60 wt% thus contributing to the reuse of waste generated by the coffee industry.
<b>Tipo</b>: article2024-03-22T11:40:13ZImproving the thickness distribution of parts with hybrid thermoforming
https://hdl.handle.net/1822/89834
Título: Improving the thickness distribution of parts with hybrid thermoforming
Autor: Duarte, F. M.; Ribeiro, Catarina G.; Ferreira, João G.; Forte, Sílvia A.; Covas, J. A.
Resumo: With the aim of improving the thickness gradient of thermoformed parts, and thus increase their performance and/or reduce their weight, the concept of hybrid thermoforming is introduced, whereby local thickness differences in extruded sheets are created prior to thermoforming. Material is removed by CO2 ablation or 3D printing of an over-thickness at specific locations of sheets previously extruded. The feasibility and potential usefulness of the approach is explored experimentally for the production of a truncated conical cup, since this is a well-characterized application. The conventional thickness distributions obtained by conventional vacuum forming are significantly changed with the new strategy and can be tuned by adequately selecting the locations and amount of material do be removed and/or added.
<b>Tipo</b>: article2024-03-22T10:41:15ZPredicting the effect of build orientation and process temperatures on the performance of parts made by fused filament fabrication
https://hdl.handle.net/1822/89831
Título: Predicting the effect of build orientation and process temperatures on the performance of parts made by fused filament fabrication
Autor: Duarte, F. M.; Covas, J. A.; Costa, Sidonie Fernandes da
Resumo: 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.
<b>Tipo</b>: article2024-03-22T10:20:29Z