1,721,008 research outputs found
Manufacturability of non-assembly joints fabricated in AlSi10Mg by selective laser melting
No full textSelective Laser Melting is a promising Additive Manufacturing technology that makes possible the fabrication of
complex metallic components up to the production of mechanisms in one technological operation without the
need for a subsequent assembly. In order to permit the one-step fabrication of the joints, a lot of issues must be
considered to preserve their functionalities. In this work some of these aspects are investigated in order to
provide a manufacturability map of non-assembly joints taking into account the clearance, the joint shape and
the building orientation.
The results show multiple behaviors mainly affected by the dropping effect which is dependent upon the local
stratification angle: a little inclination of the joint improves its functionality and widens the manufacturability
window that permit to fabricate a working joint. The clearance and joint shape have combined effects on the
torque necessary to move the joint
Interference fit of material extrusion parts
No full textMaterial extrusion is an Additive Manufacturing process able to fabricate a physical object directly from a virtual model using layer by layer deposition of a thermoplastic filament extruded by a nozzle. The fabrication of functional components implies the need for the assembly with other parts with different properties in terms of material and surface quality. One of the most used assembly method involving plastic materials is the interference fit. It consists of fastening elements in which the two parts are pushed together, by means of a fit force, and no other fastener is necessary. It requires the accurate design of the interference, typically carried out by the designers through diagrams and theoretical formulations supplied by the material manufacturers. At present no theory has been provided for material extrusion parts due to the anisotropic behavior: the mesostructure, the surface roughness and the dimensional deviations mainly depend upon the build orientation.
In this work the effects of the surface morphology and the interference grade on the assembly and disassembly forces in an interference fit joint are investigated. For the purpose, a design of experiment with a factorial plan has been carried out. The coupling behavior and the maximum forces are discussed. A new variable namely the real interference has been introduced and a relationship between this variable and the assembly force has been found. Through this model it is possible to know in advance the force necessary to assemble a material extrusion part with an assigned interference grade
Powder bed monitoring via digital image analysis in additive manufacturing
Full text linkDue to the nature of Selective Laser Melting process, the built parts suffer from high chances of defects formation. Powders quality have a significant impact on the final attributes of SLM-manufactured items. From a processing standpoint, it is
critical to ensure proper powder distribution and compaction in each layer of the powder bed, which is impacted by particle size distribution, packing density, flowability, and sphericity of the powder particles. Layer-by-layer study of the process can provide better understanding of the effect of powder bed on the final part quality. Image-based processing technique could be used to examine the quality of parts fabricated by Selective Laser Melting through layerwise monitoring and to evaluate the results achieved by other techniques. In this paper, a not supervised methodology based on Digital Image Processing through the build-inmachine camera is proposed. Since the limitation of the optical system in terms of resolution, positioning, lighting, field-of-view, many efforts were paid to the calibration and to the data processing. Its capability to individuate possible defects on SLM parts was evaluated by a Computer Tomography results verification
Effect of laser remelting on surface roughness and microstructure of AlSi10Mg selective laser melting manufactured parts
No full textSelective laser melting (SLM) allows to obtain components by a careful selection of process parameters. This technology is becoming more and more attractive because it is capable of producing dense and complex metallic parts. Considering that one of the main drawbacks of this technology is the high surface roughness, this research aims at reducing it by means of skin laser remelting performed during the fabrication process. Since the remelting strategy affects only the external skin, the building time is slightly affected by this additional operation and the infill part properties remain unchanged. In this work, the effect of process parameters on the surface morphology and alloy microstructure has been analyzed. The obtained results highlighted that the remelting process allows to improve the surface morphology but it affects the subsurface defect formation. The obtainable surface roughness for different surface slopes was modelled as a function of the process parameters
Characterization of laser treated steels using instrumented indentation by cylindrical flat punch
No full textThe aim of the present work is to assess the possibility of predicting the thickness of the hardened layers produced by High Power Diode Laser (HPDL) heat treatment. Instrumented indentation by cylindrical flat punch was carried out in order to evaluate the effectiveness of the surface-hardening heat treatments on milled AISI 1040 steel substrates by varying laser operational parameters as well as the morphology of steel substrates. In particular, the trend in load-penetration depth were obtained, supporting the identification of the depth at which the hardened layer starts transferring the deformation to the softer substrate, that is, the Critical Transition Depth (CTD) in addition to identifying the overall degree of hardening reached by the laser treated material. On the other hand, hardness profiles and the thickness of hardened layers were also monitored by using combination of Vickers micro-hardness tests and standard metallographic characterizations. Analytical examinations and simple mathematical simulations of the experimental results coming from indentation tests and conventional testing procedures showed good correlation between the extent of the heat affected zone (HAZ), hardness and CTD. In conclusion, this study demonstrates that indentation tests are an effective, sensitive, fast, and low-cost characterization technique for heat treated steels. (C) 2007 Elsevier B.V. All rights reserved
Forme metropolitane ed infrastrutture. Il caso veneto
No full textIl contributo inquadra il sistema infrastrutturale veneto all'interno delle dorsali principali dell'intermodalità comunitaria (UE), anche e soprattutto in relazione al nuovo corridoio recentemente individuato e certificato in ambito europeo: il Baltic Adriatic Corridor (BAC). La presenza di almeno tre fasci infrastrutturali fondamentali della vision comunitaria nel territorio veneto rafforza e sostanzia gli stessi caratteri metropolitani dell'intero sistema regionale e nord-estino in generale, evidenziando in maniera ormai sicura la presenza e il consolidamento di una piattaforma territoriale strategica di primaria importanza. Sembra essere maturo ormai il tempo di affrontare in maniera opportuna la "individuazione" della Città Metrolitana del Veneto Centrale, anche se purtroppo le ultime indicazioni normative in materia di città metropolitane sembrano rivolgersi più al versante burocratico-amministrativo che all'effettivo governo della realtà socio-economica esistente
Introduzione. Quali infrastrutture per quale struttura territoriale?
No full textIl contributo funge da problem posing/introduzione al volume, concettualizzando il problema/tema del rapporto tra mobilità – infrastrutture - territorio mediante una riflessione sulla situazione dello stato dell’arte nel dibattito sul paradigma della mobilità/accessibilità rispetto al tema della pianificazione, lasciando agli interventi dei diversi autori l’onere di sottolineare processi, temi e soluzioni (problem solving) che, attraverso approcci ora qualitativi ed ora quantitativi, individuano strategie ed applicazioni, esplorando altresì gli aspetti differenti del tema
Mold replication in injection molding of high density polyethylene
No full textIn order to deepen the mechanisms at the basis of mold surface replication onto the molded plastic surface, a novel experimental approach is proposed. Up to 20 different mold surface textures were made by machining with repetitive patterns of peaks and valleys. Mold replication tests were performed by over-molding of high density polyethylene (HDPE) on steel inserts. The surface morphology of inserts and injection molded parts was acquired by surface analyzer, and all the main roughness parameters were extracted and compared as well as the geometrical profiles. Surface morphology was also measured on molded samples after thermal relaxation at 100°C. As expected, a strong correlation was found between the roughness of mold insert and molded part over the full experimented range. Profiles on the molded surface have the same repetitive pattern of the corresponding insert surface but with lower peaks, higher valleys, and a horizontal shrinkage. Comparing molded HDPE surface profiles before and after thermal relaxation, it was observed a similar change to the one highlighted between mold insert and molded part. This occurrence suggests that the final surface appearance of the molded part is also a function of the relaxation mechanism during or immediately after injection molding
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