1,720,963 research outputs found
Dynamic depreciation for parts produced using laser-based powder bed fusion of polymers
No full textLaser-based powder bed fusion of polymers (PBF-LB/P) is one of the most widely used additive manufacturing technologies for producing complex and customized components. One of the key aspects of this process is the recycling of the powder, which is central to the technology’s overall efficiency. During reuse cycles, the powder undergoes inevitable chemical, physical and mechanical changes that directly affect the quality of the final artifacts. This directly impacts process sustainability and production costs. The Sum-of-the-Year’s Digits (SOYD) depreciation model, which has been proposed in the literature for metal powders, assumes an initial moderate decline in value, followed by a slower decline upon reuse. However, polymer powders can degrade more quickly than metal powders, reaching a point of no return sooner. Therefore, the SOYD model has been modified by introducing a nonlinear function to better reflect the non-constant loss of value of the powder. Initially, the loss of value accelerates, then stabilizes, and accelerates again towards the end of the powder’s useful life. The proposed depreciation model was used in a case study with two scenarios, which considered the varying residual economic values of recycled polyamide 12 (PA12) powder. The analysis shows that the method used to calculate powder reuse, whether in processing cycles or hours, can significantly impact on the overall material cost and, consequently, the final product cost
Benchmarking of FDM Machines through Part Quality Using IT Grades
Full text linkThe diffusion of Fused Deposition Modeling (FDM) was recently boosted by the expiration of the FDM patent and the subsequent worldwide development of low cost FDM machines by a huge number of small companies. In most of the cases, FDM machines are worth what they cost. Thus the performance of expensive industrial FDM systems is better than that of low cost machines, also known as 3D printers. In this paper a benchmarking is carried out between a Dimension EliteTM by Stratasys and a 3D TouchTM by Bits from Bytes (BFB). The study and comparison is based on a reference part that was designed to fit into the building volume of most of low cost FDM machines. The part includes several classic geometries (planes, cylinders, spheres and cones) of different sizes to cover several ranges of basic sizes as defined by the ISO 286 standard. Geometric features appear both in the concave and convex shapes to account for all design possibilities. The proposed reference part allows to consider a higher number of features for each range of basic sizes with respect to other benchmarking models presented in the literature. Moreover the part does not require support structures for its production, allowing for manufacturing on 3D printers that come with a unique extruder. Replicas of the reference part are printed out of ABS (acrylonitrile butadiene styrene) material with different layer thicknesses using the compared machines. After inspecting the replicas by means of a Coordinate Measuring Machine (CMM), the dimensional accuracy of the compared FDM systems is reported through part quality using IT grades associated with the ISO basic sizes. GD&T values are also evaluated for some of the geometric features appearing on the reference par
Effect of recycled powder and gear profile into the functionality of additive manufacturing polymer gears
Full text linkPurpose
Polymer laser powder bed fusion (PBF-LB/P) is an additive manufacturing technology that is sustainable due to the possibility of recycling the powder multiple times and allowing the fabrication of gears without the aid of support structures and subsequent assembly. However, there are constraints in the process that negatively affect its adoption compared to other additive technologies such as material extrusion to produce gears. This study aims to demonstrate that it is possible to overcome the problems due to the physics of the process to produce accurate mechanism.
Design/methodology/approach
Technological aspects such as orientation, wheel-shaft thicknesses and degree of powder recycling were examined. Furthermore, the evolving tooth profile was considered as a design parameter to provide a manufacturability map of gear-based mechanisms.
Findings
Results show that there are some differences in the functioning of the gear depending on the type of powder used, 100% virgin or 50% virgin and 50% recycled for five cycles. The application of a groove on a gear produced with 100% virgin powder allows the mechanism to be easily unlocked regardless of the orientation and wheel-shaft thicknesses. The application of a specific evolutionary profile independent of the diameter of the reference circle on vertically oriented gears guarantees rotation continuity while preserving the functionality of the assembled mechanism.
Originality/value
In the literature, there are various studies on material aging and reuse in the PBF-LB/P process, mainly focused on the powder deterioration mechanism, powder fluidity, microstructure and mechanical properties of the parts and process parameters. This study, instead, was focused on the functioning of gears, which represent one of the applications in which this technology can have great success, by analyzing the two main effects that can compromise it: recycled powder and vertical orientation during construction
Evaluation of the flexural behaviour of 3D printed multimaterial beams
Full text linkAmong Additive Manufacturing (AM) processes, Fused Deposition Modelling (FDM), more popularly renown as 3D printing1, allows the fabrication of multimaterial parts by extrusion of multiple thermoplastic filaments that are then deposited layer after layer. In such a way parts are built bottom to top and the different materials can be deployed in each cross section according to strategies aiming at optimizing the reinforcement through the exploitation of the design freedom of AM technologies. Most diffused commercial materials for FDM are Acrylonitrile Butadiene Styrene (ABS) and the biodegradable PolyLactic Acid (PLA), that are amorphous polymers characterized by similar mechanical properties. The use of semicrystalline polymers in FDM is often avoided because of the higher amount of shrinkage which causes the warpage of the deployed layers during manufacturing. The innovative aspect of this paper is the use of a filament made of a Polyammide (PA) blend as a reinforcement in multimaterial beams of PLA that are fabricated by FDM. The flexural behaviour of the composite beams is evaluated by three point bending tests according to the ASTM D790 method. Owing to the lack of a specific reference for 3D printing, dimensions of the specimens are assumed equal to those of injection molded specimens. Their nominal overall dimensions are 3.25 x 12.7 x 127 mm. In this preliminary study, test specimens are 3D printed with a core of PA having a rectangular cross section, whose width (w) and height (h) are varied. Bending tests show that the PA core increases both the flexural stiffness and the flexural strength of the PLA beam. Experimental results are compared with those of the finite element (FE) simulation of the bending test performed by using Abaqus/CAE software. 3D printing issues are also considered and discussed along with the influence of the layer by layer fabrication on the beam resistance
Proposal of an Innovative Benchmark for the Evaluation of 3D Printing Accuracy for Photopolymers
No full textIn recent years, the diffusion of additive manufacturing (AM) or 3D printing (3DP) techniques for polymers have been boosted by the expiration of earlier patents from the last century and the development of low-cost machines. Since these technologies become more widespread, there is a need to assess the capability and accuracy of low-cost machines in terms of dimensional and geometric tolerance. To this aim, this work proposes an innovative reference part for benchmarking layerwise processes that involve the curing of photopolymers. The geometry of the part is conceived to include several classical shapes that are easily measurable for defining the part accuracy in terms of ISO IT grades and GD&T values. Two replicas of the reference part were fabricated by stereolithography (SLA) and digital light processing (DLP) using two machines and related proprietary materials by Sharebot Company. The replicas were printed with a layer thickness of 50 μm for the DLP process and 100 μm for the SLA one. The results of dimensional measurements of the replicas, that were carried out using a Coordinate Measuring Machine (CMM), show that the geometric accuracy of the time-consuming DLP process is slightly better than that of stereolithography
A preliminary study about high-pressure homogenization as a viable alternative to produce powder feedstock for selective laser sintering of biopolymers
No full textSelective laser sintering is an established technique for producing complex plastic components, yet its broader adoption is limited by the scarcity of commercially viable materials. This study evaluates high-pressure homogenization, a fully mechanical process, for producing micronized biopolymer particles as a sustainable feedstock for selective laser sintering. The biopolymer powder was characterized in terms of morphology and flowability, followed by processability validation on a selective laser sintering machine using both simple and more complex geometries. The resulting 3D printed components were assessed for dimensional accuracy and subjected to dynamic mechanical characterization. By offering an industrially scalable method for biopolymer powder production, high-pressure homogenization expands material options for selective laser sintering, advancing sustainable additive manufacturing
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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