1,721,064 research outputs found
A Review of Waterjet Cutting Research towards microAWJ and the Definition of the Waterjet Digital Twin
Full text linkThis review paper aimed to draw the red line passing through almost 25 years of research on waterjet cutting carried out at WJ_Lab, the waterjet laboratory of the Department of Mechanical Engineering of Politecnico di Milano. The purpose was not to just historically analyse the obtained scientific results by themselves but to make them even more useful by introducing the concept of the waterjet digital twin passing through the accuracy improvements due to microAWJ. This strategy effectively creates synergy among the topics and gives the opportunity to researchers in this field to both have an example of how research in industrial manufacturing processes can be guided by scientific and industrial needs, at least from the author’s point of view, and to appreciate how it can be made useful for further improvements by introducing a powerful concept as the digital twin
Airborne acoustic emission of an abrasive waterjet cutting system as means for monitoring the jet cutting capability
Full text linkAbrasive waterjet cutting is a manufacturing technology making use of a high-speed waterjet with abrasive particles in suspension, for cutting materials with different mechanical properties. Product quality requirements are pushing towards an improvement of tracking and stabilization methods of the relevant process variables. Amongst those, the jet kinetic power defines the cutting capability and has a significant impact on the final cut features. This variable is subject to relevant fluctuations versus time. Besides, the current state of the art does not provide means for its in-line monitoring. The aim of this contribution is to monitor the airborne acoustic emission of an abrasive waterjet cutting head and investigate its correlation with the jet kinetic power. The investigation is carried out by means of factorial studies, in which the jet is fired at various water pressures and abrasive feed rates, providing different kinetic powers. The acoustic emission is synchronously monitored by means of a condenser microphone, installed on the cutting head. Data at frequencies above 40 kHz is found to constitute a robust and selective acoustic signature of the airborne jet. The acoustic signature is proven to be an effective in-line indicator of the jet kinetic power and its pressure-induced variations, whilst abrasive-induced variations remain undetected. A calibration procedure is presented, for translating the acoustic data into a jet kinetic power. The method is validated by means of further experiments that envisage its deployment in a real scenario. Overall, the presented method constitutes a robust tool for monitoring pressure-induced variations of the jet cutting capability
La consulenza etica in ambito clinico
No full textUn'analisi di che cosa sia la consulenza etica in ambito clinic
Automatic identification of edge chipping defects in high precision drilling of cemented carbide
Full text linkAutomatic visual inspection methods for product quality checking are spreading more and more in the present 4.0 manufacturing industry. This paper addresses the automatic inspection of edge integrity in accurate holes obtained by direct drilling of cemented carbide with innovative diamond coated tools. These revolutionary cutting tools, recently appeared on the market, can process extremely hard carbide in the sintered state, with massive increase of productivity with respect to standard methodologies like electrical discharge machining (EDM). However, due to the brittleness of the materials, the mechanical cutting process becomes critical and sensitive to tool breakage and workpiece defects generation. In particular, chipping of the hole edges represents one of the most important issues to monitor and take under control. A software procedure, that analyses high-resolution images taken from optical microscopes, was then developed for that aim. Image processing algorithms were designed and applied to enable the automatic extraction of the holes profile, thus permitting the identification and quantification of the leading edge damage in the radial direction. The proposed approach is fully automatic and is based on a profile segmentation that exploits an edge detection algorithm followed by a contour extraction method based on the solution of a partial differential equation. Dedicated metrics were specifically developed to evaluate the extracted profiles. The approach was validated with a factorial plane involving 1.6 mm diameter holes generated with different cutting parameters and tools on tungsten-carbide (WC) material. The technique resulted suitable for the aim, enabling the automatic characterisation of the defects generation phenomenon throughout the entire tools life. This moves a step toward the implementation of both in-line hole inspection procedures and advanced drilling process control
Investigation of the influence of the AWJ-specific energy on the cutting kerf profile on aluminium 6082
Full text linkThis study introduces the abrasive waterjet specific energy as a novel physical quantity to characterize the taper ratio in abrasive waterjet cutting. Said quantity was defined as a proper combination of the most influential control factors. A series of abrasive waterjet cutting experiments on aluminium 6082, were conducted, according to the design of experiments methodology. For each experimental run, the width of the kerf profile was measured and characterized in terms of taper ratio. The effect of the abrasive waterjet specific energy and the main process parameters on the measured quantities were investigated. Results showed that inside the experimental range of the process parameters, the abrasive waterjet specific energy correlates well with the taper ratio. As a conclusion, different combinations of the control factors (water pressure, abrasive mass flow rate, feed rate), corresponding to the same level of abrasive waterjet specific energy, produced the same cutting kerf geometry as well as the same taper ratio. This result gives freedom to the waterjet users in selecting the best parameter combination according to some criteria (e.g., time or cost) for achieving the target AWJ-specific energy and the consequent kerf quality
Operational vibration of a waterjet focuser as means for monitoring its wear progression
Full text linkAbrasive waterjet cutting is a competitive manufacturing technology in the aerospace, defense, and automotive industries. End-user requirements are currently pushing machine builders to improve the automation of their processes, in an effort to reduce costs and downtimes, as well as increase robustness and stability. On this regard, the waterjet focuser is a critical component, as its fast wear progression requires constant human supervision, for promptly detecting detrimental effects on the cutting performance. This paper describes an innovative approach for in-line monitoring the wear progression of a waterjet focuser, by means of an accelerometer installed on its tip. This result is allowed by two separate studies of the focuser, of which the first investigates the sensitivity of its first mode frequency to the wear progression, while the second demonstrates the possibility of tracking said frequency from the in-line vibration signal delivered by the accelerometer, during operation. The presented setup makes use of low-cost sensing hardware that can be easily retrofitted into the design of waterjet focusers. The information delivered is expected to tackle end-user requirements for improved process automation
Micro extrusion of high aspect ratio bi-lumen tubes using 17-4PH stainless steel feedstock
Full text linkThe manufacturing of metallic micro multi-lumen tubes of high length to diametrical aspect ratio for biomedical and multi-fluidic applications is still a challenge for the current manufacturing methods. The recent research advancements suggested metal particles loaded feedstock extrusion processing as a highly promising method for manufacturing metallic micro multi-lumen tubes where conventional metal extrusion and other feedstock processing technologies are constrained. Feedstock extrusion of micro multi-lumen tubes was inhibited by the absence of understanding on extrusion behavior of feedstocks for attaining high aspect ratio parts. The feedstock micro extrusion processing also experienced difficulties in maintaining the geometrical accuracy and surface finish due to lack of knowledge on influence of extrusion parameters on the properties of the extruded parts and absence of a quality control strategy during extrusion. In this research work, the effect of feedstock extrusion parameters on the dimensional variation as well as surface finish of the extruded multi-lumen tubes are studied by extruding high aspect ratio micro bi-lumen tubes using biocompatible grade 17-4PH stainless steel feedstock. A methodology called ‘product fingerprint’ combined with multi-objective optimization on the basis of ratio analysis (MOORA) method has been studied to assure the quality of the tubes in-line by identifying and monitoring very specific features of the tubes at optimum process conditions. The study showed that extrusion parameters such as extrusion temperature and screw speed have significant influence on diameters, roundness of the tube as well as lumens and the surface roughness. High aspect ratio bi-lumen tubes of optimum dimensional quality with an average green state areal surface roughness value of 1.97 μm were achieved at optimum process parameters levels. This research demonstrated how to manufacture micro bi-lumen tubes made of 17-4PH stainless steel with unrestricted length and even more, control their quality by monitoring couple of identified product fingerprint features of bi-lumen tube, such as external diameter of tube as well as its roundness and varying the process parameters
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