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Digital manufacturing is one of the enabling methodologies associated with the concept of flexible mass customization, which has been boosted by the recent advances in Additive Manufacturing (AM) technologies, from which complex freeform geometries, internal and reentrant features can be reproduced based on the CAD model. From the standpoint of coordinate metrology, AM calls for a measurement technology capable of acquiring high data density of these complex structures. Computed Tomography (CT) is the technology of choice to holistically measure them and respond to the needs of mass customization. However, due to the complexity of the CT measurement chain, the numerous influence factors, and their difficult quantification, the measurement uncertainty evaluation remains an issue yet to be resolved. In this regard, one topic that has received attention is the determination of the geometric errors of the CT instrument, which cause errors to dimensional measurements. Using an imaging method to quantify the geometric errors, process behavior charts are detailed and used to check the consistency of the CT measurement process with regard to the geometric errors. The utilization of process behavior charts is the major contribution of this work since they allow us to operate the measurement process up to its full potential, and to evaluate the actual effectiveness of the imaging method to quantify the errors.

Robot-CT is drawing great attention for its potential to support highly flexible scan trajectories and various scan modes with a single system. However, the quality of CT reconstruction largely dep...

Laser powder bed fusion (L-PBF) allows the production of metal lattice cellular structures with tailored mechanical properties. In order to generate the specific structural behavior it is of utmost importance to understand the response of the unit cells when different load conditions are considered. In this article the mechanical response of diamond based cellular structures has been investigated focusing on the impact of geometrical inaccuracy generated by the manufacturing process on the elastic anisotropy of the mentioned unit cell. The μ-CT analysis of the structures shows that the manufacturing deviations occur in certain orientations that depend highly on the building direction and proximity to nodes. The measured imperfection types were implemented in a finite element model in order to predict their single and combined effects in the elastic directional response. The results indicate that the L-PBF process can induce a significant change of elastic anisotropy in the diamond unit cells, including a substantial variation of the optimal orientation for minimal compliance. Methods are presented to calculate this anisotropy such that it can be taken into account when designing and using such lattice structures in real-life applications with multi-axial load conditions.

The characteristics of the X-ray focal spot strongly influence XCT image sharpness and structural resolution. However, current international standards only yield a limited characterization of the focal spot as two perpendicular sizes. Therefore, this paper presents a method for full characterization of the focal spot in terms of both 2D shape and intensity distribution, by applying the inverse Radon transform on a radiograph of a Siemens star. The method is validated through simulations and applied experimentally to two XCT sources. Subsequently, an investigation on how the X-ray tube settings influence focal spot size, shape, intensity and stability is presented.

This paper reports on the results of a round robin test conducted by ten X-ray micro computed tomography (micro-CT) laboratories with the same three selected titanium alloy (Ti6Al4V) laser powder bed fusion (L-PBF) test parts. These parts were a 10-mm cube, a 60-mm long and 40-mm high complex-shaped bracket, and a 15-mm diameter rod. Previously developed protocols for micro-CT analysis of these parts were provided to all participants, including suggested scanning parameters and image analysis steps. No further information on the samples were provided, and they were selected from a variety of parts from a previous different type of round robin study where various L-PBF laboratories provided identical parts for micro-CT analysis at one laboratory. In this new micro-CT round robin test which involves various micro-CT laboratories, parts from the previous work were selected such that each part had a different characteristic flaw type, and all laboratories involved in the study analyzed the same set of parts. The 10-mm cube contained subsurface pores just under its top surface (relative to build direction), and all participants could positively identify this. The complex bracket had contour pores around its outer vertical sides, and was warped with two arms deflected towards one another. Both of these features were positively identified by all participants. The 15-mm diameter rod had a layered stop/start flaw, which was also positively identified by all participants. Differences were found among participants for quantitative evaluations, ranging from no quantitative measurement made, to under and overestimation of the values in all analyses attempted. This round robin provides the opportunity to highlight typical causes of errors in micro-CT scanning and image analysis as applied to additively manufactured parts. Some workflow variations, sources of error and ways to increase the reproducibility of such analysis workflows are discussed. The ultimate aim of this work is to advance the efficient use of micro-CT facilities for process optimization and quality inspections for additively manufactured products. The results provide confidence in the use of laboratory micro-CT but also indicate the need for further development of standards, protocols and image analysis workflows for quantitative assessment, especially for direct and quantitative comparisons between different laboratories. ispartof: Additive Manufacturing vol:30 status: Published online

The occurrence of keyhole porosity in selective laser melting (SLM) has so far not been quantified systematically using X-ray computed tomography (X-CT). In this study, keyhole porosity in selective laser molten Ti-6Al-4V grade 23 parts was analyzed using post-process characterizations. Single tracks were produced with optimum, high volumetric energy density and low volumetric energy density parameters on the top of SLM substrate. High volumetric energy density was achieved by either (i) high laser power and optimum scan speed to study the effect of laser power or (ii) optimum laser power and low scan speed to study the effect of scan speed. Keyhole porosity is sensitive to the SLM process parameters. It was observed by using X-CT that a high amount of keyhole porosity was formed below the line scan produced with a high volumetric energy density achieved by optimum laser power and low scan speed; however, a line scan produced with same volumetric energy density but achieved by high laser power and optimum scan speed resulted in less or no voids. The X-CT porosity analysis helped to understand the size, shape, location, and number of keyhole pores that were formed.

Computed Tomography (CT) has been used in an upward trend to inspect dimensional and geometric characteristics of manufactured parts. The complexity of the measurement chain, however, gives rise to many influence factors that affect the measurement accuracy. Some of these factors are under the control of the user, who needs to properly set some CT instrument parameters for a specific measurement task. Over other influence factors, the user may have some degree of control, such as the interaction of the x-rays with the physical matter, which produces image discrepancies. Finally, there are some influence factors over which the user may have no control at all, such as misalignments resulted from imperfections of the CT instrument hardware. In this regard, this paper describes the experimental evaluation of the geometric errors of a cone-beam CT instrument using an image-based method to map them. The experiments were performed under different test conditions, designed with the main purpose of understanding the behavior of the geometric errors in time and space, as well as assisting the appropriate actions to be taken for e.g. error correction by software. Special attention was given to the evaluation of the effectiveness of the measurement method itself to detect the geometric errors.

This chapter focuses on the hardware of current and emerging X-ray computed tomography (CT) systems. First, the basic configuration of industrial cone-beam X-ray CT systems is recalled. Subsequently, individual hardware components, such as sources, detectors and kinematic systems, are described. The chapter continues with an overview of novel developments that expand the application domain of X-ray CT towards, for example, larger objects or fully integrated in-line systems. The chapter is concluded by a description of key safety elements for operation of X-ray CT systems.

X-ray computed tomography (CT) is slowly conquering its space in the manufacturing industry for dimensional metrology and quality control purposes. The main advantage is its non-invasive and non-destructive character. Currently, CT is the only measurement technique that allows full 3D visualization of both inner and outer features of an object through a contactless probing system. Using hundreds of radiographs, acquired while rotating the object, a 3D representation is generated and dimensions can be verified. In this research, this non-contact technique was used for the inspection of assembled components. A dental cast model with 8 implants, connected by a screwed retained bar made of titanium. The retained bar includes a mating interface connection that should ensure a perfect fitting without residual stresses when the connection is fixed with screws. CT was used to inspect the mating interfaces between these two components. Gaps at the connections can lead to bacterial growth and potential inconvenience for the patient who would have to face a new surgery to replace his/hers prosthesis. With the aid of CT, flaws in the design or manufacturing process that could lead to gaps at the connections could be assessed. ispartof: pages:1-11 ispartof: Dimensional Optical Metrology and Inspection for Practical Applications V, 98680G vol:9868 pages:1-11 ispartof: Dimensional Optical Metrology and Inspection for Practical Applications location:Baltimore - USA date:17 Apr - 17 Apr 2016 status: published

Within the field of quality control and dimensional metrology, the evolutions in the domain of production processes are triggering more use of non-contact measurement equipment to assure faster feature assessment where possible. This led to the development of for instance laser line scanners. The standardization of these new tools follows these novel evolutions. As the coordinate measuring systems (CMSs) which include coordinate measuring machines (CMMs) with its diversity in measurement probes widens its spectrum, the ISO 10360 standard series is rearranged and split up in more parts, covering specific probe groups. The previously mentioned laser line scanners, that can be equipped on a CMM, are integrated within ISO 10360-8 which applies for CMMs equipped with optical distance sensors. This paper is an example of how to interpret and apply this standard to a specific optical distance sensor. This has to be done by taking into account the sensor’s characteristics. The intrinsic properties in the technique require an in-depth look at the recommended guidelines within the standard. Furthermore, the guidelines are adapted to use the same capabilities of the laser line scanner, which are used for measuring, without eliminating the uncertainties present in practical use of the sensor. The verification tests and their implementation are discussed, adapted to the sensors needs and performed on a state-of-the-art CMM. The verification parameter results are determined, presented and critically evaluated. ispartof: Proc. SPIE 9868, Dimensional Optical Metrology and Inspection for Practical Applications V vol:9868 ispartof: SPIE 9868, Dimensional Optical Metrology and Inspection for Practical Applications V location:Baltimore, USA date:17 Apr - 17 Apr 2016 status: published

Full geometrical alignment of CT instruments remains a complicated endeavor. This paper therefore presents a fast and comprehensive method for determination and compensation of geometrical misalignments. First, a reference object, consisting of spheres mounted on a carbon fiber tube, is X-ray imaged at different angular positions. Subsequently, the misalignment parameters of the CT instrument are determined by minimizing the residual errors between observed and modelled sphere center coordinates. Finally, the FDK-based tomographic reconstruction algorithm is adapted to account for the determined misalignment parameters. The paper discusses the fundamentals of the approach and provides an experimental validation of its performance.