1,720,966 research outputs found
Enhancing optical measuring systems for manufacturing process control
Full text linkModern industries are stressed by the market for a crazy and continuous reduction of time-to-market and an increase of required quality of final products. Manufacturing should evolve in order to satisfy market, by increasing the process complexity and fighting against requirements (in terms of batch sizes and tolerances). Production should be fast and accurate and this implies that measuring systems have to be faster, more flexible and possibly in-line, in order to continuously adjust the process. Optical metrology seems to be the perfect solution for this challenging context. However, optical metrology is characterized by binding physical limitations that reduce accuracy and sometimes applicability. Nevertheless, the exponential increase of computational power helps the evolution and optimization of optical measuring systems by permitting real time corrections and fast post-process. The aim of this work is the development of different correction and numerical methods to enhance optical measuring system capabilities. Confocal microscopy, optical CMM (coordinate measuring systems) and X-ray computed tomography are analysed in different types of applications, ensuring a reduction of measuring process variability and increasing measurement accuracy. Algorithms developed specifically for quantification and minimization of influencing factors are presented and implemented for real time correction and control of manufacturing process. Void pixels in confocal microscopy are studied and managed, thus reducing variability of surface roughness parameters and increasing capabilities of measuring instrument for micro-milling process control. Optical systems are analysed for thread measurements proposing a correction method for inline, fast and reliable evaluation of threads geometry. Finally, surface roughness is taken into account for correction of computed tomography dimensional measurements. Different technologies applied in different fields are joined by the common need of correction for enhancing measuring capabilities
Correction of the systematic error due to imperfect multisensor registration in freeform measurements
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Effect of void pixels on the quantification of surface topography parameters
No full textIn the last decades the measurement of surface topographies was further developed using the capabilities of 3D optical profilers based on different measuring principles. These instruments have significant advantages over contact stylus measuring instruments but also some limitations. One limitation is depending from the interaction of the surface with the numerical aperture of the objective. Because of the surface slope, some parts of the surface are not correctly detected by the instrument, resulting on void pixels i.e. missing information on the measured topography. Data generated using fitting algorithms can be used to reconstruct the surface and replace the missing data, and the way this operation is performed affects the evaluation of surface parameters. As an alternative, the calculation of parameters may be performed on non-reconstructed datasets. In this work, the effect of void pixels on the determination of 3D parameters on different manufactured surfaces has been investigated using computer simulation starting from actual measurement data. Both randomly distributed and slope-dependent void pixels are considered. A sensitivity analysis with different distributions of void pixels as well as the effect of increasing slope are also presented
Metis naviga verso lo scafo riciclabile!
No full textIl gruppo di studenti universitari MètisVelaUnipd (www.metisvela.dii.unipd.it), nato nel 2008, si inserisce all’interno del progetto 1001VelaCup (www.1001velacup.eu), che prevede la progettazione, realizzazione e conduzione di scafi a vela da regata per un confronto tra vari atenei italiani ed europei sulla base di un regolamento che impone la lunghezza fuori tutto (4.6 m), la superficie velica complessiva (33 m2) e i materiali utilizzabili, lasciando liberi gli altri parametri di progetto, e favorendo quindi la ricerca di nuove soluzioni creative. La regola principale e più restrittiva riguarda i materiali: il 70% in peso dello scafo deve avere origine animale o vegetale. Le prime due imbarcazionidel gruppo padovano, Argo (2008) e Aura (2009), sono state costruite in legno mentre le due successive, Areté (2012) e Ate (2016), sono prodotte con un composito con fibra di lino e core in balsa
A machining strategy to fulfil geometrical quality requirements in cryogenic turning of acetabular cups made of Additive Manufactured Ti6Al4V
No full textAdditive Manufacturing (AM) techniques are more and more employed in the biomedical industry to produce surgical implants made of Ti6Al4V alloy. After the AM process, some finishing machining operations are still required to obtain the final product geometry. In recent years, cryogenic cooling has been adopted to improve the Ti6Al4V poor machinability, but mainly in rough machining operations. The adoption of cryogenic cooling can cut down the cleaning and sterilizing costs of biomedical components due to the drastic reduction of residual pollutants on the parts. This paper investigates the feasibility of cryogenic cooling using LN2 when finishing turning AM acetabular cups made of Electron Beam Melted (EBM) Ti6Al4V, focusing on geometrical accuracy. A preliminary study conducted on a test specimen, showed that the most critical thermal induced dimensional errors are caused by the progressive tool holder contraction and that they can be limited by acting on the cutting length. On the basis of these findings a temperature-dependent correction of the tool trajectory can be implemented to achieve the required dimensional accuracy of the acetabular cup when machined under cryogenic cooling
Influence of surface roughness on computed tomography dimensional measurements
No full textX-ray computed tomography (CT) is increasingly used in dimensional metrology. However, several influencing factors affect CT dimensional measurements. In particular, significant deviations can be observed between CT and tactile measurements especially when measuring parts with rough surfaces. The dependence of such deviations from surface morphology has not been thoroughly studied yet. In this work, the influence of surface roughness on CT dimensional measurements is investigated considering the combined effect of surface morphology and CT measurement characteristics. Experimental investigations and numerical simulations are used to determine the systematic effect on CT dimensional measurements for roughness profiles with different material distribution
Micro-drilling and Threading of the Ti6Al4 v Titanium Alloy Produced through Additive Manufacturing
No full textThe paper presents the evaluation of the drillability characteristics of the Ti6Al4 V titanium alloy produced through the Additive Manufacturing (AM) technology called Direct Metal Laser Sintering (DMLS). Holes of 1.6 mm diameter were drilled on a 5-axis high-precision micro-milling machine under dry cutting conditions at varying cutting speed and feed rate. A specific measurement procedure was developed to quantify and compare the most representative geometrical features (diameter and perpendicularity) of the machined holes as well as the quantification of burrs. The influence of the AM material on the geometrical quality of high precision holes is discussed, taking into account the requirements of the following threading operations. Finally, thread milling experiments were carried out to prove the threading feasibility and performances based on the previous drilling experiments. From the results within the tested range of cutting conditions, the lowest values of the cutting speed and feed rate seem to be the best trade-off for achieving the required hole quality
Case study: The application of machining-conditioning to improve the wear resistance of Ti6Al4V surfaces for human hip implants
No full textFeasibility of Cryogenic Cooling in Finishing Turning of Acetabular Cups Made of Additive Manufactured Ti6Al4V
No full textAdditive Manufacturing (AM) techniques are more and more employed in the biomedical industry to produce surgical implants made of Ti6Al4V alloy. After the AM process, some finishing machining operations are still required to obtain the final product geometry. In recent years, cryogenic cooling has been adopted to improve the Ti6Al4V poor machinability, but mainly in rough machining operations. This paper investigates the feasibility of cryogenic cooling when finishing turning AM acetabular cups made of Electron Beam Melted (EBM) Ti6Al4V, focusing on the obtainable surface integrity and geometrical quality, compared to dry cutting. Experimental outcomes highlight that cryogenic cooling is feasible for short turning lengths to limit tool holder contractions
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