Additive manufacturing has gained considerable attention in recent years due to its capabilities of producing complex parts with tailormade mechanical properties. Because of its infancy state, additive manufacturing production chains are seldom optimized to the same extent as conventional manufacturing techniques. Companies with additive manufacturing production sitesusing powder as a building material often find themselves devoting a lot of resources towards depowdering, a post processing step that has potential of being a significant bottleneck.The purpose of this master thesis was to develop a de-powdering system that would function automatically, relieving operators from performing the process step manually. The following work has been conducted at Sandvik in Sandviken at the department for additive manufacturing.Results were acquired with high credibility due to a mixture of qualitative and quantitative gathering techniques that supplemented each other. Together with a literature review, empirical data gave rise to the possibility of developing a new de-powdering system for binder jetting technology.Optimization of the system indicated that larger inlets produced a higher removal efficiency. This was later confirmed with computational fluid dynamics, where smaller nozzles created a more turbulent air flow, making it difficult for powder particles to exit the system. Though final trials with green bodies revealed that the system, in its current state, did not have the capabilities of replacing manual de-powdering completely, it certainly displayed how efficient it can be with further development.

Electron Beam Powder Bed Fusion manufacturing of components is an additive manufacturing process that is complex and has widespread advantages for aerospace and many industrial processes. It reduces costs and has a larger powder particle size requirement. This gives the benefit of a higher mass deposition rate and thus faster production time compared to Laser-Powder Bed Fusion process. Powder bed manufacturing processes often lead to columnar grain structure formation along the build direction, resulting in components that have anisotropic physical and mechanical properties. This is a major problem that limits the applications of this technique. In order to promote equiaxed grains, as well as refine the columnar morphology and eliminate anisotropic properties, the roles of process conditions and presence of inoculants or heterogeneous nucleating sites are considered. In this study, the addition of titanium nitride inoculants is used to promote columnar to equiaxed grain transition in ferritic stainless steel with the use of melting strategies and variable process parameters. It has been found that the thermal gradient (G) to solidification rate (R) ratio (G/R ratio) controls grain morphology and texture: a low G/R ratio has been shown to promote the formation of equiaxed grains. The process conditions for this transition were investigated. The samples were analyzed after printing single line tracks in the Freemelt One machine, and thereafter studied with the aid of optical microscopy to ascertain the combination of machine parameters that results in a successful transition from columnar grains to equiaxed. The study concluded that there was an increase in the fraction of equiaxed grains under these conditions; a low thermal gradient, high scanning velocity and low area energy. Ultimately, further investigation will be needed to establish the exact process parameters that will promote the transition from columnar to equiaxed grains in ferritic stainless steel. The findings from this study can be used by future researchers to create solidification maps for this steel grade and assist industry to tailor specific textures in ferritic stainless steel to achieved desired microstructures and mechanical properties. / Electron  Beam  Powder  Bed  Fusion  (E-PBF)  tillverkning  av  komponenter  är en  additiv tillverkningsprocess  som  är  komplex  och  har  omfattande fördelar  för  flyg  och  många industriella processer. Det minskar kostnaderna och har ett större krav på pulverpartikelstorlek. Detta ger fördelen av en högre massavsättningshastighet och därmed snabbare produktionstid jämfört med Laser-Powder Bed Fusion-processen. Tillverkningsprocesser för pulverbädd leder ofta  till  att en kolumnformig  kornstruktur  bildas  längs  byggriktningen, vilket resulterar  i komponenter  som  har  anisotropa  fysikaliska  och mekaniska egenskaper.  Detta  är  ett  stort problem som begränsar tillämpningarna av denna teknik. För att främja likaxliga korn, samt förfina den kolumnära morfologin och eliminera anisotropa egenskaper, övervägs rollerna för processbetingelser och närvaron av ympmedel eller heterogena kärnbildningsställen. I denna studie  används  tillsatsen  av  inokulanter  av  titannitrid  för  att  främja  kolumnär  till  likaxlig kornövergång  i  ferritiskt rostfritt  stål  med  användning  av  smältstrategier  och  variabla processparametrar.  Det  har  visat  sig  att  förhållandet  mellan  termisk gradient  (G)  och stelningshastighet   (R)   (G/R-förhållande)   styr   kornmorfologi   och   textur:   ett   lågt   G/R- förhållande har visat sig främja bildningen av likaxliga korn. Processförhållandena för denna övergång undersöktes. Proverna analyserades efter att ha skrivit ut spår med en rad i Freemelt One-maskinen  och  studerades  därefter  med  hjälp  av  optisk mikroskopi  för  att  fastställa kombinationen   av   maskinparametrar   som   resulterar   i   en   framgångsrik   övergång   från kolumnära  korn till  likaxliga.  Studien  drog  slutsatsen  att  det  fanns  en  ökning  av andelen likaxliga korn under dessa förhållanden; en låg termisk gradient, hög avsökningshastighet och låg areaenergi. I slutändan kommer ytterligare undersökningar att behövas för att fastställa de exakta processparametrarna som kommer att främja övergången från kolumnära till likaxliga korn i ferritiskt rostfritt stål. Resultaten från denna studie kan användas av framtida forskare för att skapa stelningskartor för denna stålkvalitet och hjälpa industrin att skräddarsy specifika texturer i ferritiskt rostfritt stål för att uppnå önskade mikrostrukturer och mekaniska egenskaper.

Additive  manufacturing  technologies  are  widely  used  in  aerospace,  space,  and  turbine industries. Parts can be manufactured directly by selectively adding materials layer-by-layer. A key aspect that is critical to the quality of the final component being manufactured is the powder characteristics. The prevailing powder characterisation techniques help in predicting the flowability of powders but do not relate to the spreading nature of the powder. To create high-quality thin layers of metal powder, it is essential to understand powder spreadability in powder bed-based additive manufacturing processes. The objective of this study was to create spreadability metrics using image analysis, mass analysis, and density analysis. A lab-scale experimental setup was constructed to replicate the powder bed-based additive manufacturing process. The impact of spreading speed and layer thickness on five different steel powders were studied using the suggested metrics. The metrics obtained powder rheometry and revolution powder analysis. The flowability parameters were compared to the spreadability analysis. Image analysis was shown to be efficient to predict the spreading nature of the powder when the processing parameters are varied. One metric, the convex hull ratio, was found to be high for  free-flowing  powders.  The  spread  area  of  free-flowing  powders  was  higher  than  the powders with poor flow properties. A mass-based analysis procedure shows that the ratio of mass deposited to the theoretical mass fluctuated in a systematic manner as a function of testing parameters  and  for  different  powders,  suggesting  that  the  mass  analysis  might  be  another potential   metric   to   assess   spreadability.   The   density-based   analysis   was   effective   in differentiating the layer density of different powders under various experimental conditions. It   is   expected   that   the   proposed   metrics   will   be   a   beginning   for  developing   further characterisation techniques. For example, the layer thickness could be studied by creating a homogenous  layer.  We  anticipate  these  metrics  to  be  used  to  develop  standardisation techniques for defining and quantifying powder spreadability, and thereby improve quality ofadditive manufacturing processes. / Additiv  tillverkning  är  teknologier  som  har  stor  uträckning  inom  flyg-,  rymd  och  turbin industrier. Delar kan bli tillverkade direkt genom att lagervis addera material på varandra. En nyckelaspekt som är kritisk till kvalitén av den slutgiltiga komponenten är egenskaperna hos pulvret. De allmänna teknikerna för pulverkarakterisering hjälper till att förutspå flytförmågan hos pulver men relaterar ej till dess spridningsförmåga. För att kunna skapa högkvalitativa skikt av  metallpulver  är  det  nödvändigt  att  förstå  pulvrets  spridningsförmåga  inom  pulverbädds baserade additiva tillverkningsprocesser. Målet  med denna studie var  att skapa ett mått för spridningsförmågan  genom  bild-  och  massanalys.  Ett  experimentellt  upplägg  i  labbskala konstruerades för att efterlikna en pulverbädds baserad additiv tillverkningsprocess. Effekten av bladets hastighet och lagrets tjocklek på fem olika pulver studerades genom användandet av de  föreslagna  mätetalen.  De  framtagna  mätetalen  jämfördes  sedan  med  existerande  pulver karakteriseringsmetoder  såsom  FT-4  Rheometer  och  pulver  analys  med  hjälp  av  roterande trumma. Slutligen så jämförs flytbarhets parametrarna med spridbarhets mätetalen. Det visar sig att bildanalysen är tillräckligt bra på att förutspå spridningsförmågan hos pulvret när  processparametrarna  låtes  vara  varierande.  Mer  specifikt  så  var  förhållandet  mellan pulvrets yta och det konvexa höljet stort för pulver som visar bra spridning. De framtagna procent  värden  från  massanalysdiagrammen  fluktuerar  vid  olika  processparametrar  hos  de olika  pulvren,  vilket  kan  betyda  att  massanalys  kan  vara  ett  potentiellt  sätt  för  att  mätta spridningsförmågan hos pulver. Det är förväntat att dessa föreslagna mätetal kommer vara början för utveckling av ytterligare karakteriseringstekniker. Till exempel, för att studera densiteten och tjockleken hos ett lager skulle man kunna skapa homogena lager. Vi förutser att dessa mätetal kommer att bli använda för att skapa standardiseringstekniker för att definiera och kvantifiera spridningsförmågan hos ett pulver och genom detta förbättra kvaliteten av den additiva tillverkningsprocessen.

The emergence of metal Additive Manufacturing (AM) over the last two decades has opened venues to mitigate the challenges associated with stochastic open-cell metal foams manufactured through the traditional foaming process. Regular lattices with user-defined unit cell topologies have been reported to exhibit better mechanical properties in comparison to metal foams which extend their applicability to multifunctional heat exchangers subjected to both thermal and mechanical loads. The current study aims at investigating the thermal-hydraulic characteristics of promising novel unit cell topologies realizable through AM technologies. Experimental investigation was conducted on four different topologies, viz (a) Octet, (b) Face-diagonal (FD) cube, (c) Tetrakaidecahedron, and (d) Cube, printed in single-cell thick sandwich type configuration in 420 stainless steel via Binder Jetting technology at same intended porosity. The effective thermal conductivity of the samples was found to be strongly dependent on the lattice porosity, however, no significant dependence on the unit-cell topology was demonstrated. Face-diagonal cube lattice exhibited the highest heat transfer coefficient and pressure drop, and consequently provided the lowest thermal-hydraulic performance. A procedure to incorporate the manufacturing-induced random roughness effects in the samples during numerical modelling is introduced. The numerical simulations were conducted on samples exhibiting the roughness profiles having statistically same mean roughness as the additively manufactured coupons and the results were compared to that obtained from the intended smooth-profiled CAD models that were fed into the printing machines. The analysis showed that inclusion of roughness effects in computational models can significantly improve the thermal performance predictions. Through this study, we demonstrate that additively manufactured ordered lattices exhibit superior thermal transport characteristics and future developmental efforts would require extensive experimentations to characterize their thermal and flow performance as well as local surface quality and AM-induced defect recognition. Experimental findings would also need to be supported by computational efforts where configurations which closely mimic the real AM parts could be modeled. A combined experimental-numerical framework is recommended for advancements in metal additive manufacturing-enabled enhanced heat transfer concepts.

Introduction of nanocarbons, such as graphene and carbon nanotubes, to metal matrices, may enhance the electrical and thermal transport, mechanical properties and some other properties of the composite materials. However, uniform distribution of the nanocarbon phase in the matrix material and manufacturing the composites in large scale can be challenging using traditional mixing methods. In this study, a facile method to fabricate metal-nanocarbon composites was developed. Firstly, copper (Cu)-polydopamine (PDA) composite was fabricated by coating Cu powders with the bioinspired PDA polymer, which was then converted to a graphite-like structure during the subsequent sintering. In terms of the properties, compared to the pure Cu sample, the Cu-PDA composite showed increased electrical and thermal conductivity, higher microindentation hardness, and enhanced wear resistance. These findings suggest the inclusion of nanocarbon phase converted from PDA can simultaneously improve the electrical, thermal, and mechanical properties of sintered Cu materials. Effect of sintering temperature and coating time (carbon content) on the microstructure and properties of the composites were discussed. Secondly, aluminum (Al)-copper nanoparticles (CuNP)-PDA composite was fabricated with a new method, to improve the sintering behavior of Al for serving as feedstock materials of additive manufacturing (AM). CuNPs were synthesized by directly reducing Cu ions in the aqueous solution. With the assistance of the PDA coating, the CuNPs can be better attached to the Al powder surfaces. The composite samples showed better sintering behavior by exhibiting higher electrical conductivities and mechanical properties, which may be due to local nanosized alloying phases generation after sintering. These findings illustrated that the composite powders could be a good candidate feedstock material for AM. The structural characterizations of the metal nanocarbon powders and the composites were performed with SEM, TEM, XRD and Raman spectroscopy. With the help of these techniques, the formation of the targeted structures in the composite was studied, including graphite-like structures of cPDA and nano alloying phases in Al-CuNP-PDA composites. Apart from the composite materials fabrication, a novel and facile manufacturing method based on metal powders was also developed. In this study, a new type of Cu- binder paste was formed, which not only can be utilized with direct ink/paste printing but also can be casted into a soft silicone rubber mold. Three-dimensional (3D) metal parts can then be subsequently obtained after sintering. Comparing to other additive manufacturing methods that involve high energy laser or electron beams, this new approach does not require expensive facilities, and it is less time-consuming. Moreover, the silicone rubber molds can be easily removed and reused. In summary, the composite powders fabricated in this study can be utilized as feedstock materials for additive manufacturing of metals and alloys. The new soft-mold casting could be used as an alternative method to manufacture 3D metal components. Therefore, the materials and the processing methods developed in the current study could have broad applications in various metal industries. / Mechanical Engineering

Fused deposition modeling (FDM) is gaining an ever increasing attention for its ability to fabricate complex geometry parts and prototypes at lower cost. The technology is striving to produce parts with high mechanical resistance that can withstand and perform under high stress environment. The adhesion strength between layers, transverse strength, is a limiting factor that need to be quantitatively evaluated to further understand and improve the bonding behavior of thermoplastic polymer in FDM. This interfacial adhesion is derived by the diffusion and penetration of polymer chains across the interface allowing the chain entanglement to form a bonding medium. This study investigates the bonding behaviour of polylactic acid (PLA) as a function of chain branching. The adhesion strength is quantitatively evaluated by developing and performing a peel test of a two-printed layer samples. It is possible to increase chain branching of PLA by bulk modification with epoxy chain extender. The modification of PLA was carried out using an internal batch mixer with four different concentrations of chain extender. The modified PLA was processed into print filament and characterized by parallel plate rheometry and DSC. It was found that the addition of chain extender increased molecular weight and degree of branching of PLA and in return the peel testing results reflected a significant increase in adhesion strength. Such improvement can be attributed to the long branched chains of PLA and its ability to create entanglements between layers. These findings can help in producing better PLA filaments to provide a higher stress resistance for FDM fabricated functional parts. / Thesis / Master of Applied Science (MASc) / Fused Deposition Modeling (FDM) is a recent popular method of plastic 3D printing technique, in which plastic filament is heated to a molten state to be then deposited through a layer-by-layer fashion to successfully fabricate parts. One of the drawbacks of that technology is the low bonding strength developed between layers as compared to strength along the length direction of layers. This study focuses on developing a testing methodology to evaluate the adhesion strength between layers and altering the material structure to maximize such strength. Four types of polylactic acid with different degrees of chain branching were successfully processed, printed and tested. Material with higher degree of branching yielded higher adhesion strength.

One of the major technical challenges with creating 3D artificial tissue constructs is the lack of simple and effective methods to integrate vascular networks within them. Without these vascular-like networks, the cells embedded within the constructs quickly become necrotic. This thesis details the use of a commercially available, low-cost, 3D printer modified with a microfluidic printhead in order to generate instantly perfusable vascular-like networks integrated within gel scaffolds seeded with cells. The printhead featured a coaxial nozzle that allowed the fabrication of hollow, gel tubes (500µm–2mm) that can be easily patterned to create single or multi-layered constructs. Media perfusion of the channels caused a significant increase in cell viability. This microfluidic nozzle design was further modified to allow for multi-axial extrusion in order to 3D print and pattern bi- and tri-layered hollow channel structures. Most available methodologies lack the ability to create multi-layered concentric conduits inside natural extracellular matrices, which would more accurately replicate the hierarchal architecture of biological blood vessels. The nozzle used in this work allowed, for the first time, for these hierarchal structures to be embedded within layers of gels in a fast, simple and low cost manner. This scalable design allowed for versatility in material incorporation, thereby creating heterogeneous structures that contained distinct concentric layers of different cell types and biomaterials. This thesis also demonstrates the use of non-extrusion based 3D biofabrication involving planar processing by means of hydrogel adhesion. There remains a lack of effective adhesives capable of composite layer fusion without affecting the integrity of patterned features. Here, silicon carbide was found for the first time to be an effective and cytocompatible adhesive to achieve strong bonding (0.39±0.03kPa) between hybrid hydrogel films. Multi-layered, heterogeneous constructs with embedded high-resolution microchannels (150µm-1mm) were fabricated in this way. With the new 3D fabrication technology developed in this thesis, gel constructs with embedded arrays of hollow channels can be created and used as potential substitutes for blood vessel networks as well as in applications such as drug discovery models and biological studies. / Thesis / Doctor of Philosophy (PhD) / Additive manufacturing (AM) involves any three-dimensional (3D) fabrication technologies that is used to produce a solid model of a predetermined design. AM techniques have recently been used in tissue engineering applications for fabrication of 3D artificial tissues that resemble architectures and material properties similar to that of the native tissue. Utilizing AM for this purpose presents the advantage of increased control in feature patterning, which leads to the realization of more complex geometries. However, there still remains a lack of simple and effective methods to integrate vascular networks within these 3D artificially engineered scaffolds and tissue constructs. Without these vascular-like networks, the cells embedded within the constructs would quickly die due to a lack of nutrient delivery and waste transport. This remains one of the biggest challenges in true 3D tissue engineering. This thesis presents a number of fast, effective and low-cost AM biofabrication techniques to address this challenge.

Industry 4.0 will pave the way to a new age of advanced manufacturing. Additive manufacturing (AM) is one of the leading sectors of the upcoming industrial revolution. The key advantage of AM is its ability to generate lightweight, robust, and complex shapes. AM can also customize the microstructure and mechanical properties of the components according to the selected technique and process parameters. AM of metals using selective laser melting (SLM) could significantly impact a variety of critical applications. SLM is the most common technique of processing high strength Aluminum alloys. SLM of these alloys promises to enhance the performance of lightweight critical components used in various aerospace and automotive applications such as metallic optics and optomechanical components. However, the surface and inside defects of the as-built parts present an obstacle to product quality requirements. Consequently, the post-processing of SLM produced Al alloy parts is an essential step for homogenizing their microstructure and reducing as-built defects. In the current research, various studies assess the optimal process mapping for high-quality SLM parts and the post-processing treatment of Al alloy parts. Ultra-precision machining with single point diamond turning or diamond micro fly-milling is also investigated for the as-built and post-processed Al parts to satisfy the optical mirror’s surface finish requirements. The influence of the SLM process parameters on the quality of the AlSi10Mg and Al6061 alloy parts is investigated. A design of experiment (DOE) is used to analyze relative density, porosity, surface roughness, dimensional accuracy, and mechanical properties according to the interaction effect between SLM process parameters. The microstructure of both materials was also characterized. A developed process map shows the range of energy densities and SLM process parameters for each material needed to achieve optimum quality of the as-built parts. This comprehensive study also strives to reduce the amount of post-processing needed. Thermal post-processing of AlSi10Mg parts is evaluated, using recycled powder, with the aim of improving the microstructure homogeneity of the as-built parts. This work is essential for the cost-effective additive manufacturing (AM) of metal optics and optomechanical systems. To achieve this goal, a full characterization of fresh and recycled powder was performed, in addition to a microstructure assessment of the as-built fabricated samples. Annealing, solution heat treatment (SHT) and T6 heat treatment (T6 HT) were applied under different processing conditions. The results demonstrated an improvement in microstructure homogeneity after thermal post-processing under specific conditions of SHT and T6 HT. A micro-hardness map was developed to help in the selection of optimal post-processing parameters for the part’s design requirements. A study is also presented, which aims to improve the surface characteristics of the as-built AlSi10Mg parts using shot peening (SP). Different SP intensities were applied to various surface textures of the as-built samples. The SP results showed a significant improvement in the as-built surface topography and a higher value of effective depth using 22.9A intensity and Gp165 glass beads. The area near the shot-peened surface showed a significant microstructure refinement up to a specific depth, due to the dynamic precipitation of nanoscale Si particles. Surface hardening and high compressive residual stresses were generated due to severe plastic deformation. Friction stir processing (FSP) was studied as a localized treatment on a large surface area of the as-built and hot isostatic pressed (HIPed) AlSi10Mg parts using multiple FSP tool passes. The influence of FSP on the microstructure, hardness, and residual stresses of parts was investigated. FSP transforms the microstructure of parts into an equiaxed grain structure. A consistent microstructure homogenization was achieved over the processed surface after applying a high ratio of tool pass overlap of ≥60%. A map of microstructure and hardness was prepared to assist in the selection of the optimal FSP parameters for attaining the required quality of the final processed parts. Micromachining to the mirror surface was performed using diamond micro fly-milling and single point diamond turning techniques, and the effect of the material properties on surface roughness after machining was investigated. The machining parameters were also tuned to meet IR mirror optical requirements. A novel mirror structure is developed using the design for additive manufacturing concept additive (DFAM). This design achieved weight reduction of 50% as compared to the typical mirror structure. Moreover, the developed design offers an improvement of the mirror cooling performance due to the embedded cooling channels directed to the mirror surface. A novel mirror structure is developed using the design for additive manufacturing concept additive (DFAM). This design achieved weight reduction of 50% as compared to the typical mirror structure. Moreover, the developed design offers an improvement of the mirror cooling performance due to the embedded cooling channels directed to the mirror surface. / Thesis / Doctor of Philosophy (PhD)

Additive manufacturing (AM) has the ability to fabricate components of high geometric complexity that are difficult or near impossible to be produced by traditional manufacturing technologies. Selective laser melting (SLM) is a commonly used AM technology for metallic fabrications. SLM offers the opportunities to customize the characteristics of the as-build part produced, by adjusting the laser settings. However, high strength aluminum (Al) alloys presents an obstacle for SLM production due to the low alloying content, which increases the alloys’ probabilities to form cracks due to thermal stress induced by the SLM build process. The current study focuses on the study of surface roughness and dimensional accuracy of SLM fabrication of Al6061 and AlSi10Mg. Using design of experiment (DOE), wide ranges SLM process parameters were experimented with, and their individual effect along with their interactive effects on the fabricated parts’ quality were evaluated. The quality characteristics studied are: microstructures, microhardness, tensile strength (ultimate tensile strength, and yield strength), density, surface roughness, and dimensional accuracy. Regression models were created for each quality characteristics, and the combination of density, surface roughness, and dimensional accuracy results was used to create processing window for SLM that ensures the production of high-quality parts. The work aims to not only be used as-is, to help with the selection of SLM process parameters for Al6061 and AlSi10Mg that will reduce the post- processing time, but also to set a foundation for future development for numerical models that could better predict and describe the relations between SLM process parameters and the part’s fundamental qualities. / Thesis / Master of Applied Science (MASc)

Additive Manufacturing has brought about substantial benefits to the manufacturing industry due to the numerous advantages it provides, at the same time there are factors that can be improved upon. Temperature control is an important parameter during the build process as it affects build quality. The main objective of this thesis project was to investigate what sensors could be used for monitoring the temperature during the additive manufacturing processand to compare and evaluate their performance. This involved implementing two 2-color pyrometers and a short-wave infrared camera to monitor the temperature of the area behind the melt pool and then visualizing the respective data. Initial issues arose during test runs in the form of noise in the pyrometer data, this was solved by implementing a smoothing filter to the signal. Multiple runs were conducted to capture the required data as images produced by the camera were overexposed and out of focus during initial runs. This was solved by changing the camera position and exposure settings. Reading the temperature values from the images involved interpreting the Average Dark Units (ADU) values of the region of interest and then comparing those values to a reference chart. The data gathered with the help of LabVIEW software and the proprietary imaging software of the camera showed that the selected sensors were in fact suitable for the intended task and could be used in conjunction with each other. This data could then be used to create a closed-loop system in the future (not in the scope of this thesis work) and thus enable the increase in the level of automation for Robotized Laser Wire Additive Manufacturing.