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The digital industrialization is revitalizing the way that manufactured products are conceived. The opportunity of several prevailing technologies allows products’ digital modelling, and enhanced productivity, with cost-efficient solutions. Even so, corresponding effective metrology methods are urgently needed to preserve the manufacturing digitalization whole perspective. In this background, an alternative assessment of optical surface topography measurements was demonstrated on micrographs’ spatial frequency content. Specifically, the power spectral density (PSD) was used for the evaluation of Sq and Sdq areal roughness parameters in a dedicated software developed in Matlab®. Initially, the dedicated software was validated against a commercial software. Afterwards, the calculation of Sq and Sdq parameters, as they are defined in the ISO 25178-2, was compared with the evaluation of the same parameters by the PSD. The results showed a broad agreement. It was found that differences were mostly due to the presence of noise. The evaluation of Sq and Sdq by the PSD is, in fact, less sensitive to noise. This was found above all for the Sdq parameter, where the approximation of the gradient in the conventional numerical evaluation can possibly enhance the influence of the noise. The PSD evaluation of Sq and Sdq was also proven more robust against different magnifications (namely different fields of view and pixel widths), retaining for the most unbiased statistical information for both 50× and 100× lens objectives. Thus, the PSD, and in general the frequency content of optical measurements, can be useful for the prediction of surface topographies based on digital modelling of measured data. It can be a manageable format of the acquired surfaces, less sensitive to noise and defects, to assist the digitalization of manufacturing.

The development of new high flux photon counting detectors (PCDs) opens the opportunity to implement energy dispersive x-ray computed tomography (XCT) systems in aviation security. This paper presents a novel prototype of an energy dispersive XCT instrument for research applications. The paper describes the instrument design and operational parameters along with a preliminary metrological investigation using a reference artefact, the CT tube, by visualisation and comparison to measurements on a coordinate measurement machine (CMM). The paper demonstrates how this novel CT instrument can, using only an extremely sparse number of 20 projections, both visualise the reference artefact with a 1 mm voxel size and be used to estimate distances with deviation from CMM around or less than half the voxel size (± 0.5 mm). This paper show that the novel prototype XCT instrument could be used to demonstrate the feasibility of a full-sized scanner design for future aviation security.

This work presents opportunities and challenges in energy dispersive CT systems for aviation security applications. Current security x-ray scanners use dual-energy systems for threat identification. Dual-energy scanners cannot clearly separate all materials, which results in high false-alarm rates and cause delays for travellers. The development of both new energy dispersive photon counting detectors and associated analysis algorithms allows for improved threat detection by employing energy dispersive scanner systems. The implementation in aviation of such systems as security x-ray scanners also poses several challenges, which are discussed in the paper.

Modern smart and intelligent manufacturing is characterised by an increasing use of highly engineered surfaces and quasi-free form geometries, for example, by additive manufacturing, and the requirement for fast and informative measurement tools for quality controls in production. These have lately pulled towards the adoption of optical surface topography measuring instruments to qualify technological surfaces, which are core to being assessed to characterise the product and optimise the manufacturing process. Surface topography measurements performed by optical instruments are known to suffer from disturbances, such as non-measured points and spikes. These are due to complex interactions between the measurand and the instrument and may result in poor measurement quality and biased characterisation results. Currently, the correction of measurement disturbances is carried out by empirical approaches which mostly involve thresholding and interpolations, whose sensitivity is often devolved to the operator. In this work, a Gaussian process regression-based approach is outlined to identify and correct measurement disturbances exploiting spatial correlation properties of the measurements to provide a formal, robust, and univocally defined approach to manage measurement disturbances. The proposed approach, differently from currently available alternatives, is capable of managing at once the different type of disturbances by means of a supervised machine learning technique. The formal and practical advantages of the proposed method are discussed exploiting case studies of industrial interest applied on quasi-flat surfaces to stress the disturbances effect.

Additive manufacturing enables the production of complex geometries, both internally and externally. This poses a challenge to quality control. Non-destructive volumetric testing methods are required. Among these methods, X-ray computed tomography is currently the most promising. It enables not only to detect inner and outer defects but also to perform dimensional measurements. However, the method lacks of metrological tracability. To fill this gap, an EMPIR project 17IND08 AdvanCT involving several European countries was proposed. In this frame, DTU Mekanik and LNE have conducted a comparison campaign of XCT systems using machined material measures representative of additively manufactured parts. The purpose of the comparison was to investigate the performances of industrial X-ray computed tomography with respect to dimensional measurements on external but also on internal features.

The increasing demand for micro-injection molding process technology and the corresponding micro-molded products have materialized in the need for models and simulation capabilities for the establishment of a digital twin of the manufacturing process. The opportunities enabled by the correct process simulation include the possibility of forecasting the part quality and finding optimal process conditions for a given product. The present work displays further use of micro-injection molding process simulation for the prediction of feature dimensions and its optimization and microfeature replication behavior due to geometrical boundary effects. The current work focused on the micro-injection molding of three-dimensional microparts and of single components featuring microstructures. First, two virtual a studies were performed to predict the outer diameter of a micro-ring within an accuracy of 10 µm and the flash formation on a micro-component with mass a 0.1 mg. In the second part of the study, the influence of microstructure orientation on the filling time of a microcavity design section was investigated for a component featuring micro grooves with a 15 µm nominal height. Multiscale meshing was employed to model the replication of microfeatures in a range of 17–346 µm in a Fresnel lens product, allowing the prediction of the replication behavior of a microfeature at 91% accuracy. The simulations were performed using 3D modeling and generalized Navier–Stokes equations using a single multi-scale simulation approach. The current work shows the current potential and limitations in the use of micro-injection molding process simulations for the optimization of micro 3D-part and microstructured components.

Injection pressure is one of the most significate factor governing the effectiveness of Molding based manufacturing processes. Being the monitoring of injection pressure easy to implement, the opportunity to address quality control on injection pressure as manufacturing fingerprint opens up to the possibility of implementing online process control solutions for Industry 4.0 approaches; examples are machine learning, deep learning and artificial intelligence. For the purpose, the calibration of process fingerprints with a quality feature of the final part is required. In this study, the injection pressure is assessed in different Injection Molding and Injection Compression Molding process conditions when replicating a polymer microstructured optical part [1]. The study case presents a high clarity polymer Fresnel lens showing a square aperture with varying low aspect ratio features. Grooves step height size ranges from 17.3 μm to 346.6 μm for peak-to-valley (PV) while the pitch has a constant value of 748.1 μm. Absolute dimensions of the grooves, as long as global part mass, are investigated in varying compression gap and holding pressure levels. Defining relationship between the geometrical dimensions of the micro structures, global mass and process fingerprint is the main outcome of this research work.

Structural colouration is a well-known “bio-inspired” phenomenon that explains the astonishing natural iridescence of several animals’ skin, such as: fish scales, birds’ feathers, butterflies’ wings, flowers and more beauties in nature. The phenomenon occurs when light diffracts due to the topology of the just mentioned surfaces independently from radiation-based colouring or pigmentation. In recent years, the rise of nanotechnology has brought about the possibility to design and reproduce structural colours on consumer products [1]. In this study, structural colours are proposed as decorative features for plastic substrates. Periodic sub-micro gratings showing a variable pitch (400 – 1500 nm) and step height (300 – 1000 nm) are manufactured in a cleanroom by means of nanoimprinting lithography on steel inserts. Gratings are subsequently replicated on plastic products by means of polymer injection moulding. This study focuses on understanding the technology readiness, highlighting limitations and advantages of the adoption of structural colours in plastic consumer products. Aspects related to different polymer replication techniques of the nanostructures, metrological challenges to ensure manufacturing accuracy and precision of the mentioned features, the durability of the plastic gratings and the durability of the nanoimprinted injection moulding inserts would be key factors in understanding the applicability of structural decoration in the plastic industry.

Injection compression molding (ICM) provides enhanced optical performances of molded polymer optics in terms of birefringence and transmission of light compared to Injection molding (IM). Nevertheless, ICM requires case-dedicated process optimization to ensure that the required high accuracy geometrical replication is achieved, particularly especially in the case of surface micro-features. In this study, two factorial designs of experiments (DOE) were carried out to investigate the replication capability of IM and ICM on a micro structured Fresnel lens. A laser scanning confocal microscope was employed for the quality control of the optical components. Thus, a detailed uncertainty budget was established for the dimensional measurements of the replicated Fresnel lenses, considering specifically peak-to-valley (PV) step height and the pitch of the grooves. Additional monitoring of injection pressure allowed for the definition of a manufacturing signature, namely, the process fingerprint for the evaluation of the replication fidelity under different process conditions. Moreover, considerations on the warpage of parts were related to a manufacturing signature of the molding processes. At last, the global part mass average and standard deviation were measured to correlate local geometrical replication performances with global part quality trends.

The importance of Additive Manufacturing (AM) in the field of micro manufacturing is increasing. Vat Polymerization Methods are one of the lead AM technologies to produce polymer micro parts. In the Technical University of Denmark (DTU), a vat photopolymerization AM machine able to print features in a micro scale was developed, build and validated. The work here presented analyses the capability of the machine in terms of geometry, when printing features of different sizes and geometries. For this study, two test parts have been designed, a circular stepped pyramid and a square stepped pyramid, both having micro size steps at the top of the pyramids. Five batches of each test part have been printed to evaluate the variability of the results in a single and in various prints.

The technological revolution that has deeply influenced the manufacturing industry over the past two decades opened up new possibilities for the realisation of advanced micro and nano systems but, at the same time, traditional techniques for quality assurance became not adequate any longer, as the technology progressed. The gap between the needs of the manufacturing industry and the well-organized structure of the dimensional and geometrical metrology appeared, above all, related to the methodologies and, also, to the instrumentation used to deal with the incessant scaling down of the critical dimensions of the novel micro and nano production. Nowadays, design methodologies and concurrent tolerance guidelines are not yet available for advanced micro manufacture. Moreover, there are no shared methodologies that deals with the uncertainty evaluation of feature of size in the sub-millimetre scale. On the other hand, a large choice of measurement equipment is now available but limitations in their use and of the instruments themselves are, in many cases, not completely understood, yet. In this context, the ambition of the PhD project was to develop and implement a complete metrological framework for advanced precision micro moulded products with micro/nano structured surfaces and micro/nano geometries, across several length scales. Uncertainty evaluation and traceability, specification intervals formulation, assessment of the moulded parts replication and a deep investigation on the optical instruments currently available for micro/nano dimensional and geometrical measurements were all subjects of the research conducted during the three years of the PhD course of study and that were collected in this final work. Traceability and uncertainty evaluation were dealt with the development of a comprehensive statistical methodology based on the well-known frequentist approach. It was successfully applied to dimensional and geometrical measurements in t

Optical instruments for areal topography measurement can be especially sensitive to noise when scanning is required. Such noise has different sources, including those internally generated and external sources from the environment.

The evaluation of an adequate and robust measuring strategy, for roughness assessment of polymer Fresnel lenses is put under assessment. An ‘on-sample’ measurement noise, is evaluated using a laser confocal microscope (OLYMPUS © Lext). Secondly, the lowest-noise roughness measuring procedure, on an injection compression moulded (ICM) Fresnel lens, is defined. A set of two different objectives is considered, i.e. a standard series (SO), against a long working distance one (LWD); two different magnifications objectives, 50x and 100x and the use or not of a dark environment. The noise evaluation is performed by comparing ‘on-sample’ noise with the one calculated on an optical flat. Noise is investigated by means of established methods, i.e. subtraction and averaging methods. Afterwards, the lowest-noise analysis is structured following a 23 full factorial experimental planning, whose factors are measuring working distance, objective magnification and room lighting. The result confirms a strong difference of noise, using the considered objectives. The most interesting result is that the performance of SO 50x objective is better than LWD 100x.

Five green and five sintered parts of a micro mechanical component, produced by micro powder injection moulding, were measured using an optical coordinate measuring machine. The aim was to establish a method for quality assurance of the final produced parts. Initially, the so called “green” parts were compared with the sintered parts (final products) calculating the percentage of shrinkage after sintering. Successively, the expanded uncertainty of the measured dimensions were evaluated for each single part as well as for the overall parts. Finally, the estimated uncertainty for the shrinkage was evaluated propagating the expanded uncertainty previously stated and considering green and sintered parts correlated. Results showed that the proposed method can be effective instating tolerances if it is assumed that the variability on the dimensions induced by the shrinkage equals the propagated expanded uncertainty.

Four specimens in the sub-micrometre range and with different polishing were topographically investigated in fiveareas over their respective surfaces. Uncertainties were evaluated with and without correction for systematicbehaviour and successively analysed by a design of experiment (DOE). Results showed that the correction forsystematic behaviour allowed for a lower value of the estimated uncertainty when the correction was adequate tocompletely recognise the systematic effects. If not, the correction can produce an overestimation of the uncertainty.

The increasing importance of optical microscopy in the geometrical and dimensional assessment of structured and freeform surfaces has easily overcome many difficulties related to the use of contact instruments. Nonetheless, some concerns related to optical instruments when measuring such surfaces are still open. The working distance (WD) of some standard (ST) lenses, e.g., can prevent from freely moving alongside features at different heights and positions of structured and freeform shapes due to the risk of collisions. In such cases, the so-called long working distance (LWD) objectives allow to operate at a longer distance from the surface under measurement, saving the same field of view (FoV) but accepting lower numerical apertures.

An international comparison of optical instruments measuring polymer surfaces with arithmetic mean height values in the sub-micrometre range has been carried out. The comparison involved sixteen optical surface texture instruments (focus variation instruments, confocal microscopes and coherent scanning interferometers) from thirteen research laboratories worldwide. Results demonstrated that: (i)Agreement among different instruments could be achieved to a limited extent; (ii) standardisedguidelines for uncertainty evaluation of areal surface parameters are needed for users; (iii) it is essentialthat the performance characteristics (and especially the spatial frequency response) of an instrument isunderstood prior to a measurement.

Precision moulding is an essential technology for the miniaturisation of moulded parts and it is continu-ously needing for specially developed solutions to face new challenges in injection moulding (IM) pro-cesses.One of the key challenges in advanced IM technology is the achievement of a full surface replication of the tool insert component when moulding the polymer melt [1]. This aspect is particularly critical when dealing with increasingly small dimensional scales in micro- and nano-structured surfaces [2, 3].In this context, a metrological investigation of polymer replicated surfaces using metal masters with different types of finish has been carried out.Four types of surface finish were considered: a) Diamond buff polishing. b) Grit paper polishing. c) Stone polishing. d) Dry blast polishing (see Fig. 1). Both master and replicated surfaces were measured using a laser scanning confocal microscope. Hence, the replication fidelity was evaluated comparing the measurements of the polymer surfaces against the ones of the masters. The amplitude and the slope replications were considered calculating respectively Sq and Sdq areal surface texture parameters. The expanded uncertainty was also evaluated according to ISO 15530-3:2011, adapted to optical measure-ments, and propagated to the replication fidelity.A good amplitude replication was achieved for stone polished surfaces with a replication fidelity larger than 90 %. The dry blast ones were evaluated with an amplitude replication fidelity of about 70 %. The worst amplitude replication was achieved for both diamond buff and grit paper polished surfaces with a replication fidelity around 50 %.The tendency is almost the same for slope replication but the replication fidelity values are lower: 70 % for stone polished surfaces. 50 % for dry blast and grit paper polished surfaces. 30 % for diamond buff polished surfaces.

A procedure for statistical analysis and uncertainty evaluation is presented with regards to measurements of step height and surface texture. Measurements have been performed with a focus-variation microscope over jet electrochemical micro-machined surfaces. Traceability has been achieved using as reference contact measurements from a calibrated stylus instrument. A statistical analysis has been carried out and the method of least squares has been implemented to correct for systematic behaviours. The combined uncertainty has been evaluated accordingly and the expanded uncertainty has been finally calculated as the confidence interval of 95 %. Results show that agreement within single digit micrometre (dimensional measurements) and tenths of micrometre (surface parameters measurements) can be achieved with the proposed methodology.