1,721,021 research outputs found
Development of generalized tool life model for constant and variable speed turning
Full text linkIn this research, a generalized tool life modelling for considering non-stationary cutting conditions was developed. In particular, for the first time in literature, the model was conceived for predicting the life of the tool when spindle speed variation SSV, one of the most effective techniques for suppressing regenerative chatter vibrations, is used. The proposed formulation takes into account the main cutting parameters and the parameters associated to the SSV. A dedicated experimental campaign of turning tests was executed and the data were used for modelling purposes. The model validation was carried out performing additional tool life tests. According to the analyzed technological scenario, it was found that the generalized formulation can be used for predicting the tool life both at constant spindle machining CSM and adopting SSV with the maximum estimating error of 6%
A novel application of cryogenics in dieless sheet metal piercing
Full text linkIn tube punching, if the internal die is necessary to properly pierce the tube avoiding its collapse, it also represents a bottleneck to a rapid change of the punching set. In this research an innovative dieless tube punching approach has been conceived and studied. The use of a cryogenic fluid to force the material ductile-brittle transition is a way to limit the sheet deformation during the piercing process. The analysis of the innovative cryogenic punching was carried out both adopting numerical and experimental methodologies. A finite element FE model of the cryogenic punching was developed and updated in two stages. First, experimental tensile tests, performed at cryogenic temperatures, were used to characterize some material properties. Secondly, some piercing tests in cryogenic conditions were performed at different velocities and temperatures to fine update the model. A validation session was carried out to assess the model and the process feasibility. It was found that the FE model reproduced the experimental results within a maximum estimation error of 10% on both the punching force and tube deflection. Results showed that both the increment of the punching velocity and especially the decrement of the punching temperature could be the only viable solution for making the tube dieless punching industrially feasible
Printability of recycled feedstock for extrusion additive manufacturing
Full text linkThe 3D printability of several thermoplastic feedstocks, recycled from post-industrial or post-consumer waste and the properties of printed items are presented and discussed. A preliminary investigation has been conducted with post-industrial scraps of PETG and PLA recycled into printable filaments. A comparison with samples produced with corresponding virgin materials showed similar mechanical characteristics. The printability of virgin, recycled and recycled/UVA exposed ABS pellets from extruded scraps is also compared. Recycled pellets were aged by exposure to UVA light up to 400 hours. The results of mechanical tests of 3D printed specimens indicate that the printability of recycled and artificially aged ABS pellets is still acceptable. Furthermore, nylon fibres recycled from clothing were used as feedstock for 3D printing. A simple and inexpensive recycling process is proposed to recover extruded pellets from nylon t-shirts. On the other hand, 3D printing tests showed that the recycled nylon has some prospects for 3D printing, but only if mixed at low percentage with virgin polymer
The propagator for a particle in a well
No full textAn elementary derivation is given for the propagator of a particle in an infinitely deep well. The time evolution of the wavefunction is illustrated through some examples, and certain general properties of the propagator are discussed. The connection with the Talbot effect and other phenomena is outlined
The propagator for a particle in a well
No full textAn elementary derivation is given for the propagator of a particle in an infinitely deep well. The time evolution of the wavefunction is illustrated through some examples, and certain general properties of the propagator are discussed. The connection with the Talbot effect and other phenomena is outlined
Multivariate analysis of mean Raman spectra of erythrocytes for a fast analysis of the biochemical signature of ageing
No full textAgeing of red blood cells (RBC) is a physiological process, fundamental to ensure a proper blood homeostasis that, in vivo, balances the production of new cells and the removal of senescent erythrocytes. A detailed characterization at the cellular level of the progression of the ageing phenomenon can reveal biological, biophysical and biochemical fingerprints for diseases related to misbalances of the cell turnover and for blood pathologies. We applied Principal Components Analysis (PCA) to mean Raman spectra of single cells at different ageing times to rapidly highlight subtle spectral differences associated with conformational and biochemical modifications. Our results demonstrate a two-step ageing process characterized by a first phase in which proteins plays a relevant role, followed by a further cellular evolution driven by alterations in the membrane lipid contribution. Moreover, we used the same approach to directly analyse relevant spectral effects associated to reduction in Haemoglobin oxygenation level and membrane fluidity induced by the ageing. The method is robust and effective, allowing to classify easily the studied cells based on their age and morphology, and consequently to evaluate the biological quality of a blood sample
Characterization of calcium carbonate nanoparticles with architectural application for the consolidation of Pietraforte
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Experimental investigation of the effects of cryogenic cooling on tool life in Ti6Al4V milling
Full text linkIn this paper, the results of an experimental campaign of cryogenic milling are presented and discussed. For this purpose, a specific experimental setup that allowed to feed the liquid nitrogen LN through the tool nozzles was used. Tool life tests were carried out at different cutting speeds. The tool duration data were collected and used to identify the parameters of the Taylor’s model. Different end-of-life criteria for the tool inserts were even investigated. The achieved results are compared to those obtained using conventional cooling. It was observed that at low cutting velocity, conventional cooling still assures longer tool lives than in cryogenic condition. Since in cryogenic milling the increasing of the cutting velocity is not so detrimental as in conventional cutting, at high cutting speed (from 125 m/min) longer tool durations can be achieved. Statistical analyses on the model parameters were carried out to confirm the presented findings. The analysis of the effect of the cooling approach on the main wear mechanisms was also reported. At low cutting speed, adhesion and chipping phenomena affected the tool duration mainly in cryogenic milling
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