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Alessandro Carrozza,Federico Mazzucato,Alberta Aversa,Mariangela Lombardi,Federica Bondioli,Sara Biamino,Anna Valente,Paolo Fino 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.9
Directed energy deposition is an additive manufacturing technology which usually relies on prototype machines or hybridsystems, assembled with parts from different producers. Because of this lack of standardization, the optimization of the processparameters is often a mandatory step in order to develop an efficient building process. Although, this preliminary phaseis usually expensive both in terms of time and cost. The single scan approach allows to drastically reduce deposition time andmaterial usage, as in fact only a stripe per parameters combination is deposited. These specimens can then be investigated,for example in terms of geometrical features (e.g. growth, width) and microstructure to assess the most suitable processwindow. In this work, Ti-6Al-4V single scans, produced by means of directed energy deposition, corresponding to a total of50 different parameters combinations, were analyzed, focusing on several geometrical features and relative parameters correlations. Moreover, considering the susceptibility of the material to oxygen pick-up, the necessity of an additional shieldinggas system was also evaluated, by comparing the specimens obtained with and without using a supplementary argon flow. A process window, which varies according to the user needs, was found together with a relationship between microstructureand process parameters, in both shielding scenarios.
A. Carrozza,B. A. Bircher,A. Aversa,S. Biamino 대한금속·재료학회 2023 METALS AND MATERIALS International Vol.29 No.12
The Ti–6Al–4V (Ti64) alloy is a well-established material to be processed via laser powder bed fusion (LPBF). Recently,other α + β titanium alloys are receiving attention, such as Ti–6Al–2Sn–4Zr–6Mo (Ti6246). Their typical industrial fields ofapplication (aerospace, automotive), often require critical design choices, such as low wall thicknesses and hollow channels. Thus, a comparative analysis between these two competitor alloys in terms of processability was conducted in this work. To do so, specific sample designs were developed. The specimens were analyzed in terms of geometrical compliance withthe initial design, porosity, and microstructure. A correlation between the width of the specimens and their porosity, microstructureand hardness was found. Overall, both the alloys proved to be well processable, even for very low wall thickness(300 μm) and channel diameter (1 mm) values. Nevertheless, the Ti6246 alloy seemed to behave better in specific scenarios. For instance, some Ti64 specimens provided delamination. The hollow channels proved to be challenging for both materials,mainly due to the high amount of residual powder particles adhered to the upper part of the holes. This works aims atgiving a materials perspective on process-related issues, considering the LPBF-induced defectology and microstructuralvariations in these Ti alloys.
Productivity Enhancement in Directed Energy Deposition: The Oscillating Scanning Strategy Approach
Alberta Aversa,Alessandro Carrozza,Giulio Marchese,Stefano Felicioni,Michele De Chirico,Mariangela Lombardi,Federica Bondioli,Paolo Fino 대한금속·재료학회 2023 METALS AND MATERIALS International Vol.29 No.7
Directed Energy Deposition (DED) is an additive manufacturing process that enables the production of large metal componentsby melting the feedstock material while being deposited. An improvement of the production speed of this processwould further increase its applicability in many industrial fields. The DED building rate is strictly related to the buildingparameters adopted, in particular to the laser spot diameter, which also affects the build accuracy and the surface quality ofthe components. The possibility of using a variable laser spot would result in a significant increase in the production rate inbulky zones, while also providing a good surface quality where needed. In the present work, an oscillating scanning strategywas used to create a large apparent laser spot (+ 170% of the nominal value) to produce 316L stainless steel samples via DED. The optimisation of the DED parameters with the oscillating strategy was performed using the single scan tracks (SSTs)approach. The morphologies of the SSTs obtained with different process parameters were assessed and the geometrical featuresrelated to the melt pools were analysed in order to select the most suitable X and Z displacements for the production ofthe cubic samples. The analyses of the cubes revealed that, if the correct overlap among nearby scans is selected, it is possibleto obtain dense samples with all the oscillating diameters tested. Finally, comparing the building rate and powder efficiencyvalues confirmed that this method can accelerate the building process and improve its overall performance.
M,J,Johnson,G,A,Di Lauro,M,C,Carrozza,E,Gugllelmelli,P,Dario 한국과학기술원 인간친화 복지 로봇 시스템 연구센터 2003 International Journal of Assistive Robotics and Me Vol.4 No.1
To reduce the potential healthcare costs arising from a rapidly aging industrial world population, the problem of sustaining independent living for the elderly and persons with low to high levels of disabilities must be addressed. Using the kitchen as a microcosmic design space for the residential environment, the proposed design solution is the development of the GIVING-A-HAND system, a low cost, modular system of aids that relies on domotic, telematic, and robotic technologies to provide more affordable and universally accessible solutions to elderly and disabled persons. This paper presents the system concept and the results of interviews with elderly and people with medium to high level functional disabilities, which prioritized and refined requirements for the robotic component of the system: a small, counter-top mobile robot, “Addams Hand” that users can remotely control to interact with typical kitchen appliances.
A Robotic System for Soft Tissue Characterization
P,Vacalebri,R,Lazzarini,S,Roccella,F,Vecchi,M,C,Carrozza,M,Zecca,P,Dario 한국과학기술원 인간친화 복지 로봇 시스템 연구센터 2003 International Journal of Assistive Robotics and Me Vol.4 No.2
A miniature robotic system has been designed and fabricated to perform in vivo mechanical characterization of soft tissues. The tissue tester employs a stepper motor, which is controlled using micro-stepping techniques to prevent irregular rotation of motor shaft at low speeds. There is also a load cell to measure the reaction force of the tissue under test. At the end of tests session, data could be post elaborated on a PC with special software that reconstructs the force-displacement curves of the tissues being tested. Position and rate feedback are implemented with a digital encoder to minimize errors in motor control during the evaluation of typical viscoelastic phenomena of biological tissues. Calibration tests indicate that the force-displacement curves of the miniature robotic indenter are consistent with that obtained using an ordinary universal testing machine.
M. Zecca,G. Cappiello,F. Sebastiani,S. Roccella,F. Vecchi,M. C. Carrozza,P. Dario 한국과학기술원 인간친화 복지 로봇 시스템 연구센터 2003 International Journal of Assistive Robotics and Me Vol.4 No.4
The development of a prosthetic hand able to replicate as much as possible the grasping and sensory features of the natural hand represents an ambitious project for scientists. State of the art technology is still far to provide engineers with components with similar performance of their natural models, and active prosthetic hands can be only a pale replication of the missing natural limb. <BR>This paper presents the current research efforts towards the development of a self-adaptative and anthropomorphic prosthetic hand. In particular, the paper is focused on the problem of replicating the natural sensory system of the hand with an artificial proprioceptive and exteroceptive sensory system.