1,112 research outputs found
Dimensional metrology and computed tomography for precision AM
No full textDimensional metrology and computed tomography for precision A
Topography characterization of additively manufactured surfaces using CT
No full textX‐ray computed tomography (CT) is increasingly used for evaluating parts produced by additive manufacturing (AM) in terms of geometrical and dimensional characteristics, internal defects, and surface topography. In particular, CT enables non‐destructive measurements of both internal and difficult‐to‐access geometries, features and surfaces (including micro-scale re-entrant surface features typical in metal AM parts), overcoming the main limitations of contact and optical measuring techniques.
This presentation deals with the ongoing research at the University of Padova (Italy) aimed at developing advanced CT-based surface topography measurement procedures to improve the understanding and precision of AM processes
X-ray computed tomography for advanced geometrical measurements of metal powders and enhanced surface topography analyses of additively manufactured parts
No full textMetal powder has a significant influence on the quality and performance of laser powder bed fusion (LPBF) processes and products. A key requirement for metal powder is to have shape and size distribution designed to have adequate flowability, packing behavior and laser absorption, as well as to fabricate parts with acceptable density, surface finish and mechanical properties. Accurate three-dimensional (3D) characterizations of powder particles are fundamental to enable relevant research, for example on powder reuse and material waste reduction in LPBF. This work studies advanced measurement approaches, based on X-ray computed tomography (CT), for the 3D geometrical characterization of powder particles. The work includes comparisons with conventional powder characterization methods, considering different materials and powder morphologies. Results show the potential of the CT-based approaches to provide accurate and complete 3D powder geometrical measurements, and to exploit the obtained results for the enhancement of surface topography analyses and LPBF development
Experimental investigations on the structural resolution in metrological computed tomography
No full textIn the recent years, X-ray computed tomography (CT) has been successfully applied as an innovative coordinate measurement technology in industrial metrology. An important metrological characteristic to be assessed during CT performance verification is the metrological structural resolution (MSR) for dimensional measurements, which describes the size of the smallest structure that can still be measured within error limits to be specified, as defined in the guideline VDI/VDE 2630-1.3. The MSR statement provides important information, especially when measuring small geometries or microstructures. The ‘Hourglass’ method, developed at the University of Padova, allows testing the MSR by using a simple geometry consisting of two touching spheres with the same diameter. In this work, latest findings are presented, based on the implementation of two different strategies for applying the ‘Hourglass’ method. Advantages in using this method are also discussed in comparison with other existing proposals and a selection of factors influencing the method were evaluated through experimental analyses
AlmaDante. Seminario dantesco 2013
No full textIl volume raccoglie alcune delle relazioni presentate alla prima edizione del seminario dantesco internazionale per dottorandi "Alma Dante", tenutasi presso l'Università di Bologna nel 2013. I quindici contributi qui raccolti sono opera di dottorandi attivi in numerose università italiane (Bologna, Roma sapienza, Pisa, Napoli, Ca' Foscari, Sassari, Parma, Firenze, Milano, Roma Tre) e straniere (Oxford, Cambridge) e spaziano su molti aspetti dell'opera di Dante, studiata sotto il profilo critico e filologico. Una premessa di Giuseppe Ledda introduce i vari contributi e il volume nel suo complesso
Dimensional metrology and non-destructive testing for additive manufacturing
No full textState-of-the-art review on dimensional metrology and non-destructive testing for additive manufacturing
Comparison of X-ray computed tomography and conventional methods for the geometrical characterization of metal powder for additive manufacturing
No full textAmong additive manufacturing technologies, laser powder bed fusion (LPBF) has experienced extensive interest in recent years from a wide range of industrial sectors, including aerospace and biomedical. One important aspect influencing the performances of processes and products is the quality of the feedstock material. In particular, metal powder used in LPBF should have shape and size promoting good flowability and packing behaviour, which have a direct impact on density, surface finish and mechanical properties of the fabricated parts. X-ray computed tomography (CT) is an advanced technique that enables holistic three-dimensional characterizations of metal powder, with simultaneous measurement of size and shape. The geometrical measurement accuracy of X-ray CT powder characterization is investigated and enhanced in this work, starting from the comparison with laser diffraction and scanning electron microscopy
X-ray computed tomography for coordinate metrology and industrial applications
No full textX-ray computed tomography (CT) has emerged as innovative measuring technique for dimensional metrology in industry over the last years. Thanks to unique capabilities, CT provides several advantages in comparison with other well-established coordinate measuring systems (CMSs). In particular, CT allows obtaining a holistic three-dimensional model of the scanned workpiece and performing non-destructive and non-contact measurements of outer as well as inner features and geometries difficult to access. However, important drawbacks limit a wider acceptance of this technology in industry. One of the most critical problems is the complexity of metrological traceability establishment due to difficulties in evaluating the task-specific uncertainty, as well as specification and determination of metrological performances of CT systems. In fact, a dedicated international standard for CT acceptance test and performance verification is still under development.
In this thesis, experimental activities were mainly oriented at evaluating and improving CT metrological performances. The material influence on length measurement errors was studied by investigations based on two reference objects: aluminium hole plate, with significant material effect and ruby ball plate, with negligible material influence. The obtained results contributed to the test survey organized on this topic by the ISO working group that is developing the future ISO standard for CT.
The image quality of the 2D projections acquired by CT is fundamental for achieving a good reconstruction quality. It is directly connected to the image blurring content and, consequently, to the focal spot quality. In this thesis, new methods developed to assess the focal spot drift and size are presented.
Considering the entire CT measurement procedure, an important metrological characteristic to be evaluated is the metrological structural resolution (MSR). Despite several methods for MSR evaluation have been proposed, a standard test to be included in the ISO standard for CT has still to be defined. In this thesis, the ‘Hourglass’ method –developed by the University of Padova– was selected to evaluate the MSR. The method was improved by measuring a high number of distances and by applying a definition of MSR similar to the one proposed by the guideline VDI/VDE 2617-13. Moreover, the method concept was compared with concepts of other proposed methods. Finally, the main influence quantities affecting the method were identified and evaluated.
Since CT is a multi-purpose measuring technique, it has become attractive for many industrial applications. However, the accuracy of CT measurement results is often unknown. For this reason, the evaluation of CT accuracy for specific measurement tasks as well as the comparison with other well-established evaluation methods is crucial for the acceptance of CT in industry. In this thesis, two industrial case studies were addressed: (i) porosity analysis for metal additive manufactured parts and (ii) wear evaluation of polymeric prosthetic components. In the first study, CT was compared with other inspection techniques such as Archimedes method, gas pycnometry and microscopic analysis of cross-sections. A multisensory CMM was used as well in order to get reliable reference area values for pores lying on selected cut sections. In the second study, the proposed CT-based method was validated through comparison with the gravimetric method, which is the current reference method used for wear assessment
- …
