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Laser powder bed fusion is a type of metal-based additive manufacturing method that can be customized for a given material through modification of process parameters, resulting in changes to the overall quality and mechanical properties of the as-built component. Optimal mechanical properties are typically achieved by performing experimental builds of fully dense components with multiple parameter sets and comparing the resulting mechanical properties. Additionally, AM allows geometric freedom that can be utilized to produce structures tailored for energy absorption, such as cellular structures or lattice structures. There is limited previous work of scaling effects on mechanical properties of cellular structures. The first part of this work aims to determine process parameters that result in the best overall mechanical properties of L-PBF manufactured maraging 300 steel. This work then uses the optimal parameters to produce cellular structures scaled both uniformly and selectively to perform mechanical and physical analysis on their response.

This thesis explores the optimization of process parameters for producing single-track thin walls using Laser Powder Bed Fusion (LPBF) additive manufacturing. Using two different coupon designs, the study assesses the feasibility of creating the thinnest possible leak-tight structures within LPBF and evaluating their mechanical properties, including burst pressure and modulus of elasticity under pressure loads. A series of experimental iterations were conducted, varying laser power and laser speed to identify optimal conditions. The findings indicate that a narrow range of process parameters can produce consistently leak-tight thin walls. The results contribute to understanding how to achieve high quality, reliable thin wall structures in the LPBF process, with implications for industrial applications requiring thin, precise, leak tight, and durable walls.

This thesis work was done to get a fundamental knowledge of the mechanical and microstructural properties of 316L stainless steel fabricated with the additive manufacturing technique, laser powder-bed fusion (L-PBF). The aims of the thesis were to study the mechanical and microstructural properties in two different building orientations for samples built in two different machines, and to summarize mechanical data from previous research on additive manufactured 316L. Additive manufacturing (AM) or 3D-printing, is a manufacturing technique that in recent years has been adopted by the industry due to the complexity of parts that can be built and the wide range of materials that can be used. This have made it important to understand the behaviour and properties of the material, since the material differs from conventionally produced material. This also adds to 316L, which is an austenitic stainless steel used in corrosive environments. To study the effect of the building orientation, samples of 316L were built in different orientations on the build plate. The density and amount of pores were also measured. Tensile testing and Charpy-V testing were made at room temperature. Vickers hardness was also measured. Microstructure and fracture surfaces were examined using light optical microscope (LOM) and scanning electron microscope (SEM). The microstructure of the 316L made with L-PBF was found to have meltpools with coarser grains inside them, sometime spanning over several meltpools. Inside these coarser grains was a finer cellular/columnar sub-grain structure. The tensile properties were found to be anisotropic with higher strength values in the orientation perpendicular to the building direction. Also high dense samples had higher tensile properties than low dense samples. The impact toughness was found to be influenced negatively by high porosity. Hardness was similar in different orientations, but lower for less dense samples. Defects due to lack of fusing of particles were found on both the microstructure sample surfaces and fracture surfaces. The values from this study compare well with previous reported research findings.

Additive manufacturing (AM) is a promising manufacturing process that provides that ability to fabricate components with complex geometries with relatively low lead times compared to other manufacturing processes. This allows for more freedom of design, as prototypes can easily be produced throughout the development process. AM is also especially beneficial in tooling applications, where internal geometries such as cooling channels are required in order to improve the quality of the manufactured parts. These geometries are more difficult to produce with more conventional manufacturing methods such as forging or casting. Currently, Laser Powder Bed Fusion (LPBF) shows the most promise in the field of Additive Manufacturing (AM) of metals, as it offers the freedom to produce complex components with little post processing required. Additionally, post processing with Hot Isostatic Pressing (HIP) can be implemented to significantly enhance the final properties of the material.  The LPBF-process can produce many different defects within the parts such as: part porosity and lack of fusion. This is mainly due to the layer-by-layer configuration of the process. Parts can also experience large thermal fluctuations and rapid cooling rates which can generate large residual stresses. This can result in significant cracking in certain high alloyed materials which can impact part quality and  material properties. If the cracking is severe enough, it will result in failure of the entire component and render the entire parts completely useless. Post processing with HIP may remove some of these defects and reduce the residual stresses in the material and thus produce a material with properties that are satisfactory. The purpose of this thesis is to investigate the processability of a high alloy cold work tool steel with LPBF. The main focus is the influence of the processing parameters and part geometry on the quality of the produced parts. Furthermore, the influence of the processing parameters on defects and microstructure will also be investigated. The aim is to produce parts that can be enhanced with HIP as a post processing treatment. Additionally, the impact of HIP on the properties of the part will also be investigated in order to determine if the there are any improvements in terms ofreduction in part defects and the removal of any undesired microstructural features which are produced from the process. The experimental results showed that the processability of the tool steel is difficult. Several sample volumes were produced with varying processing parameters and scanning strategies, and all the specimens from all sample volumes exhibited some cracking. Parts produced with a combination of contouring and hatching strategy, where there is an internal structure showed the most promise, as these parts exhibited the least amount of severe cracking. However, additional research of the processing parameters and scanning strategies is required in order to reduce the amount of cracking of the external shell structure and thus, achieve proper densification of the parts when post processing with HIP. / Additiv tillverkning (AM) är en lovande tillverkningsprocess som ger möjligheten att tillverka komponenter med komplexa geometrier med relativt låga ledtider jämfört med andra tillverkningsprocesser. Detta ger större frihet i under designprocessen eftersom prototyper enkelt kan produceras under hela utvecklingsprocessen. AM är också särskilt fördelaktigt i verktygstillämpningar, där interna geometrier såsom kylkanaler krävs för att förbättra kvaliteten på de tillverkade delarna. Dessa geometrier är svårare att tillverka med mer konventionella tillverkningsmetoder som smidning eller gjutning. För närvarande visar det sig att Laser Powder Bed Fusion (LPBF) är det mest lovande inom området additiv tillverkning av metaller, eftersom processen erbjuder friheten att producera komplexa komponenter samt att efterbearbetning som krävs blir mindre. Dessutom kan efterbearbetning med Hot Isostatic Pressing (HIP) implementeras för att avsevärt förbättra materialets slutliga egenskaper. LPBF-processen kan ge upphov till många olika defekter i delarna såsom: delporositet och lack of fusion. Detta beror främst på att processen sker lagervis vilket kan ge upphov att många småfel. Delar kan också uppleva stora termiska fluktuationer och snabba kylningshastigheter som kan generera stora restspänningar. Det kan resultera i stor sprickbildning i vissa höglegerade material vilket kan påverka delarnas kvalitet och materialegenskaper. Om sprickorna som bildas är stora eller djupa nog kommer detta att resultera i att hela komponenten blir oanvändbar. Efterbearbetning med HIP kan ta bort en del av dessa defekter och minska restspänningarna i materialet och därmed producera ett material med goda egenskaper. Syftet med detta arbete är att undersöka bearbetbarheten hos ett höglegerat kallbearbetningsstål med som produceras med LPBF. Huvudfokus är påverkan av processparametrar och detaljgeometrin på kvaliteten på de producerade delarna. Vidare kommer också processparametrarnas inverkan på defekter och mikrostruktur att undersökas. Syftet är att producera delar som kan förbättras med HIP som efterbehandlingsbehandling. Dessutom kommer effekterna av HIP på delens egenskaper också att undersökas för att avgöra om det finns några förbättringar i termer av minskning av deldefekter och avlägsnande av alla oönskade mikrostrukturella egenskaper som produceras från processen. De experimentella resultaten visade att verktygsstålets bearbetbarhet är svår. Flera provvolymer producerades med varierande processparametrar och skanningsstrategier, och alla prover från alla provvolymer uppvisade viss sprickbildning. Delar som tillverkats med en kombination av kontur och hatch, där det finns en inre struktur visade sig mest lovande, eftersom dessa delar uppvisade minst sprickbildning. Ytterligare arbete av processparametrarna och skanningsstrategier krävs dock för att minska mängden sprickbildning i den yttre skalstrukturen och därmed uppnå korrekt förtätning av delarna vid efterbearbetning med HIP.

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Laser-based additive manufacturing offers a high degree of thermokinetic flexibility that has implications on the structure and properties of the fabricated component. However, to exploit the flexibility of this process, it is imperative to understand the process-inherent thermokinetic evolution and its effect on the material characteristics. In view of this, the present work establishes a fundamental understanding of the spatiotemporal variation of thermokinetics during the fabrication of the non-ferrous alloys using the laser powder bed fusion process. Due to existing limitations of experimental techniques to probe such thermokinetics, a finite element method-based computational model is developed to predict the thermokinetic variations during the process. With the computational approach coupled with experimental techniques, the current work presents the solidification behavior influenced by spatially varying thermokinetics. In addition, it uniquely predicts the process-inherent multi-track multi-layer evolution of thermal cycles as well as thermal stress cycles and identifies their influence on the post-solidification microstructural evolution involving solid-state phase transformation. Lastly, the response of the material with a unique microstructure is recorded under various conditions (static and dynamic), which is again compared with the same set properties obtained for the same material processed via conventional routes.