To Örebro University

In this work, aluminium–carbon-fibre reinforced plastic joints have been studied. Three types of samples were designed as double lap joints where the aluminium inserts were fabricated using both classical methods (milling) and additive manufacturing. Two versions of the joint were fabricated using additive manufacturing, one flat, and the other with small teeth designed to hook into the carbon-fibre plies. The joints were characterised using a non-linear, dual-energy computed tomography method to evaluate the bond between the composite and the metal inserts. The mechanical strength of the bonds was evaluated, both through tensile tests and four-point bending. A simple finite element model was used to discuss the joints behaviour. It was found that the joints fabricated using additive manufactured inserts were more resistant to peel stress than the milled inserts. In four-point bending tests the moment that the joint could withstand was increased by roughly 300% with the use of additive manufacturing and 400% with the use of additive manufacturing and small teeth. However, in tensile tests it was found that the teeth design reduced the maximum load capacity of the joints by roughly 30% due to porosity. Further, it was found that the additive manufactured samples did not add to the capability of withstanding shearstress. The information gained with the dual-energy computed tomography method was highly valuable as the behaviour of the joints would have been difficult to explain without the porosity information.

In this work the effects of fabrication errors in the Body Centered Cubic strut lattice, and the periodic surface lattice Schwarz Diamond has been investigated. The lattices were both fabricated as-is and with induced errors to evaluate the lattices response to fabrication errors. The behaviour of the lattices were studied using compression test and in-situ computed tomography investigation. The results show that the Schwarz Diamond lattices in general are stronger than the Body Centered Cubic lattices in all of the measured aspects. Often up to five times stronger. It was also found that the elastic behaviour of the Schwarz Diamond lattices were mainly unaffected by fabrication errors while the Body Centered Cubic lattices experienced severe losses in performance. The behaviour of the lattices under compression could be followed using computed tomography which aided in the understanding of their behaviour.

Fused deposition modeling (FDM) is one of the most common additive manufacturing (AM) techniques for fabricating prototypes as well as functional parts. In this technique, several parameters may influence the part quality and consequently mechanical properties of fabricated components. In this paper, an experimental investigation on effects of fabrication temperature as one of the influential parameters on mechanical properties of manufactured parts is presented. A series of specimens fabricated at temperatures ranging from 180 to 260 ^∘C were used for this investigation. X-ray computed tomography (CT) was used in order to non-destructively analyze the internal geometry of the specimens especially the bond between extruded filaments. Finally, the specimens were subjected to a uniaxial tensile load for evaluation of mechanical properties. The results showed that the specimens fabricated at lower temperatures have relatively lower tensile strength despite their considerably higher strain at break. In addition, the specimens fabricated at higher temperature range had significantly higher tensile strength because of the better bond between extruded filaments. The different mechanical responses were highly related to the internal geometry of the specimens and not necessarily the porosity. CT showed great potential as a non-destructive tool for investigation and development of FDM process.

Wire drawing is a cold work metal forming process which is dependant of a functional lubrication process. If the lubrication fails, there is a risk that both the tools and the produced wire will be damaged. Process monitoring of wire drawing is rare in today’s industry since there are no commercialised methods that deliver consistent results. In this paper, a method for monitoring of the wire drawing process is proposed and evaluated. A thermal imaging camera was used for acquiring thermal images of the wire as it leaves the drawing tool. It was found that the proposed method could capture changes in the wire drawing process and had correlation to the drawing force. An equation for estimating the friction condition between the wire and the drawing die using the wire temperature was also proposed and evaluated against experiments. The results showed that the new equation produced results that correlated well to results obtained using a conventional equation that use drawing force.

The complexity of the components fabricated in today's industry is ever increasing. This is partly due to market pressure, but it is also a result from recent progress in fabrication technologies that open up new design possibilities. The increased use of additive manufacturing and multi-material systems, especially, has driven the complexity of parts to new heights. The new complex material systems bring benets in many areas such as; mechanical properties, weight reduction, and multifunctions. However, the increased complexity also makes inspection and dimensional control more dicult. In additive manufacturing, for example, internal features can be fabricated which cannot be seen or measured with conventional tools. There is thus a need for non-destructive inspection methods that can measure these geometries. Such a method is X-ray computed tomography. Computed tomography utilizes the X-rays ability to penetrate material to create 3D digital volumes of components. Measurements and material investigations can be performed in these volumes without any damage to the investigated component. However, industrial computed tomography is still not a fully mature method and there are many uncertainties associated with the investigation technique. In this work, a dual-energy computed tomography tool has been developed with the aim to increase the performance of computed tomography when investigating complex geometries and material combinations. This method has been applied to various phantoms and an industrial case. Also, in this work, complex lattice structures fabricated with additive manufacturing have been investigated and analysed using computed tomography. The results show that the new DECT method improves measurement results and can be utilized to inspect multi-material components. The results also show that computed tomography can be used successfully to gain knowledge about complex lattices.

Industrial computed tomography of multi-material objects can be problematic due to difficulties in optimising the x-ray spectra of the scan. A possible solution to the problem is to use two x-ray spectra when scanning objects. The results from such scans can be fused into a single data-set that contains enhanced information. This practice is known as dual-energy computed tomography (DECT). In this work, the aim was to investigate two DECT methods ability to improve measurements in multi-material phantoms. To determine the performance of the methods three different phantoms containing precision spheres as measurement objects were investigated. To improve measurements in this work was defined as improving the measurement consistency of diameter measurements. The phantoms were also scanned with a single setting for comparison. The fusion of the data-sets was done using two methods, a linear fusion, and a novel non-linear fusion. Both of the methods relies on pre-reconstruction fusion of data-sets. The results show that both of the DECT methods improved measurement results significantly compared to the reference method. Further, the results show that the novel non-linear DECT method produces more accurate measurement results compared to the linear method.

Today many manufacturing plants are getting increasingly digitized to stay competitive. Data from the production machines can be transferred to a central storage/cloud for process/factory surveillance and for optimizing the processes. However, first data must be acquired. Wire drawing machines are seldom equipped with sensors that measure product quality, tool wear or the condition of the lubrication. This work presents concepts, experience and applications, of such sensors for wire drawing machines.

The use of commodity polymers such as polypropylene (PP) is key to open new market segments and applications for the additive manufacturing industry. Technologies such as powder-bed fusion (PBF) can process PP powder; however, much is still to learn concerning process parameters for reliable manufacturing. This study focusses in the process–property relationships of PP using laser-based PBF. The research presents an overview of the intrinsic and the extrinsic characteristic of a commercial PP powder as well as fabrication of tensile specimens with varying process parameters to characterize tensile, elongation at break, and porosity properties. The impact of key process parameters, such as power and scanning speed, are systematically modified in a controlled design of experiment. The results were compared to the existing body of knowledge; the outcome is to present a process window and optimal process parameters for industrial use of PP. The computer tomography data revealed a highly porous structure inside specimens ranging between 8.46% and 10.08%, with porosity concentrated in the interlayer planes in the build direction. The results of the design of experiment for this commercial material show a narrow window of 0.122 > Ev > 0.138 J/mm3 led to increased mechanical properties while maintaining geometrical stability.

Additive manufacturing (AM) in the last decade has become a widespread manufacturing process. The possibilities that such technologies have provided for manufacturing of complex geometries compared to conventional manufacturing processes has made them popular in many branches of industry. Despite the advantages of these methods, there are limiting issues which needs to be thoroughly investigated. A limiting factor, especially for powder bed AM parts is their undesired surface finish. AM surfaces can be investigated using various methods such as optical or tactile methods, however for complex AM surfaces they are incapable of capturing all details such as deep valleys at surface level. X-ray computed tomography (CT), can provide 3D information of complex AM surfaces and does not have limitations that line of sight and tactile methods have. There are several parameters in CT investigation, which can potentially alter the obtained results. Depending on the CT magnification at which the data is acquired the result specifically surface level detail might be affected. The aim of this study is to investigate the effect of different CT magnifications on surface texture measurement of additively manufactured surfaces. Surface features, including highest peaks and deepest valleys contributing to maximum and minimum thickness of specimen from different magnifications were compared with each other. The result shows that, the lower magnification scans underestimate both peak and valley measurements in comparison to the highest magnification scan. Measurement of valleys and re-entrant features were underestimated at more considerable level. The results from this study provide some understanding regarding surface morphology assessment of AM parts and the level of detail which can be expected depending on the CT magnification.

X-ray computed tomography is a highly versatile investigation method with applications in a wide range ofareas. One of the areas where the technique has seen an increased usage, and an increased interest from industry,is in dimensional metrology. X-ray computed tomography enables the measurement of features and dimensionsthat are difficult to inspect using other methods. However, there are issues with the method when it comes tomeasurements of objects that consist of several materials. In particular, it is difficult to obtain accurate computedtomography results for all materials when the attenuation of materials differs significantly. The aim of this workwas to measure small air gaps between different materials using dual-energy X-ray computed tomography. Thedual-energy method employed in this work uses two energy spectra and fuses the data in the projections spaceusing non-linear fusion. The results from this study show that the dual-energy method used in this work was ableto capture more measurements than regular absorption computed tomography in the case of specimens withhighly different attenuation, enabling, in particular, the measurement of smaller gaps. The contrast-to-noise ratiowas also increased significantly with the use of dual-energy.