The purpose of this thesis is to effectively model the time history of the temperature distribution during the selective laser sintering process and use this information to investigate the resulting relative density. The temperature is a critical parameter of the process because it directly effects the overall quality of the part. First, an efficient, affordable, and reliable simulation was developed within the finite element software, Abaqus. Next, the results from the simulations were compared to the experimental results performed by Wang et al. (2016). The FEA model consisted of a 3 layer simulation. Multiple simulations at various laser recipes were conducted using W-Ni-Fe as the powder material. The P/v (laser power/scanning speed) was plotted against the resulting total time above the melting temperature for various simulation. It was concluded that a linear relationship exists between the P/v parameters used in the laser recipe and the resulting time above the melting temperature. The average R2 values for the W-Ni-Fe simulations for layer 1, 2, 3 were 0.962, 0.950, and 0.939, respectively. Additionally, the experimental results from the Wang et al. (2016) study confirmed that a linear relationship is present. Thus, it can be concluded that the P/v parameters used within the laser recipe has a direct relation to the resulting relative density of the SLS part.

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No description available.

No description available.

The main problem encountered in this thesis is the lack of research and knowledge of selective laser melted-printing with Uddeholm Dievar®. This absence of information could cause issues regarding quality and properties of the alloy as well as uncertainty regarding an appropriate heat treatment cycle. This thesis mainly focuses on observing the changes that occur in the microstructure when Uddeholm Dievar® is manufactured through the additive manufacturing (AM) method known as selective laser melting (SLM). The SLM- method consists of a high-power laser that melts together thin layers of powder, one layer at a time, until a three-dimensional product is created according to selected drawings. The methodology on which this thesis is based on is the execution of a theoretical study, scientific experiments and thermodynamic calculations. Analysis of the microstructure is performed using a scanning electron microscope with techniques such as Energy-dispersive X-ray spectroscopy (EDS) and Electron backscatter diffraction (EBSD). The purpose of the methods are to map the constituent elements of the alloy and observe the orientation of the crystallographic phases in the atomic lattice respectively. The results show that the powder, both before and after printing, mainly consists of martensite with a low amount of residual austenite. The amount of primary carbides is relatively low and has been classified as MC (V-rich) and/or M6C (Mo- rich) type. The remaining residual austenite could be explained by the segregation of constituent alloying elements, where the carbon content is a dominant factor to why the MS -temperature lowers significantly causing the presence of retained austenite even though SLM has a cooling rate that varies between 103 and 108 [K/s]. / Det huvudsakliga problemet som denna avhandling behandlar är bristen på forskning och kunskap inom selective laser melting (SLM) 3D-printing med Uddeholm Dievar®. Avsaknaden kan leda till sämre kvalité och produktegenskaper hos legeringen. Det kan även leda till ovisshet gällande val av lämplig värmebehandling. Arbetet fokuserar på att dokumentera utformningen av stålets mikrostruktur när Uddeholm Dievar® tillverkas med den additiva tillverkningsmetoden SLM. Tillverkningsprocessen består av en högeffektslaser som detaljerat smälter samman tunna lager pulver, ett lager i taget, tills att en tredimensionell produkt skapats utefter valda ritningar. Använda metoder är; utförandet av en teoretisk studie, vetenskapliga experiment och thermodynamiska beräkningar. Analys av mikrostrukturen genomförs med hjälp av svepelektronmikroskåp där teknikerna Energy-dispersive X-ray spectroscopy (EDS) och Electron backscatter diffraction (EBSD) används. Syftet med EDS är att kartlägga de ingående elementen i legeringen, syftet med EBSD är att se orientering av de kristallografiska faserna i atomgittret. Resultaten visar på att legeringen, både före och efter printing, till största del består av martensit med en låg mängd restaustenit. Mängden primärkarbider är relativt låg och har klassifiserats som typen MC (V-rik) och/eller M6C (Mo- rik). Den kvarstående restausteniten kan möjligen förklaras av segringen av ingående legeringsämnen där kolhalten är en dominerande faktor som sänker MS-temperaturen. Detta gör att restaustenit förekommer trots den höga kylhastigheten som varierar mellan 103 och 108 [K/s] i SLM.

Cette étude acoustico-perceptive concerne les limites de la perception et de la production des voyelles orales du français [i, e, ɛ, a, u, o, ɔ, y, ø, œ], en isolation et en contextes consonantiques divers, chez dix tchécophones, futures enseignantes de Français Langue Étrangère (FLE). Les résultats montrent que (1) La maîtrise phonétique des voyelles dépend de leurs graphies et de l’entourage consonantique. (2) Les voyelles fermées [i, y, u] et le [a] sont globalement maîtrisées avec authenticité. (3) Les capacités de perception des contrastes entre les voyelles moyennes e/ɛ, ø/œ et o/ɔ ainsi que leur production sont limitées. Ces résultats ne sont que partiellement en accord avec les prédictions établies à partir du Speech Learning Model (SLM) de Flege (1995), basé sur la notion de similarité phonétique qui existe entre la langue maternelle (LM) et la langue étrangère (LE). / This acoustic-perceptual study concerns the limits of perception and production of French oral vowels [i, e, ɛ, a, u, o, ɔ, y, ø, œ], in isolation and in different consonantal contexts, in ten pre-service Czech teachers of French as a Foreign Language (FFL). The results show that (1) Phonetic proficiency in vowels depends on their spellings and consonantal context. (2) Vowels [i, y, u] and [a] are generally mastered with authenticity. (3) The ability to hear contrasts between the vowels e/ɛ, ø/œ and o/ɔ and pronounce them is limited. These results are only partially consistent with the predictions established in the Speech Learning Model (SLM) by Flege (1995), based on the notion of phonetic similarity between the mother tongue (MT) and the foreign language (FL).

Cette étude acoustico-perceptive concerne les limites de la perception et de la production des voyelles orales du français [i, e, ɛ, a, u, o, ɔ, y, ø, œ], en isolation et en contextes consonantiques divers, chez dix tchécophones, futures enseignantes de Français Langue Étrangère (FLE). Les résultats montrent que (1) La maîtrise phonétique des voyelles dépend de leurs graphies et de l’entourage consonantique. (2) Les voyelles fermées [i, y, u] et le [a] sont globalement maîtrisées avec authenticité. (3) Les capacités de perception des contrastes entre les voyelles moyennes e/ɛ, ø/œ et o/ɔ ainsi que leur production sont limitées. Ces résultats ne sont que partiellement en accord avec les prédictions établies à partir du Speech Learning Model (SLM) de Flege (1995), basé sur la notion de similarité phonétique qui existe entre la langue maternelle (LM) et la langue étrangère (LE). / This acoustic-perceptual study concerns the limits of perception and production of French oral vowels [i, e, ɛ, a, u, o, ɔ, y, ø, œ], in isolation and in different consonantal contexts, in ten pre-service Czech teachers of French as a Foreign Language (FFL). The results show that (1) Phonetic proficiency in vowels depends on their spellings and consonantal context. (2) Vowels [i, y, u] and [a] are generally mastered with authenticity. (3) The ability to hear contrasts between the vowels e/ɛ, ø/œ and o/ɔ and pronounce them is limited. These results are only partially consistent with the predictions established in the Speech Learning Model (SLM) by Flege (1995), based on the notion of phonetic similarity between the mother tongue (MT) and the foreign language (FL).

Additive Fertigungsverfahren stellen in den letzten Jahren einen Megatrend dar, da sich mit diesen Verfahren endkonturnahe Werkstücke mit hohem Materialausnutzungsgrad herstellen lassen. Die auch als 3D-Druck bekannt gewordenen additiven Fertigungsverfahren sind jedoch nicht auf die Prototypenfertigung aus Kunststoffen begrenzt. Beim selektiven Laserschmelzen werden metallische Werkstoffe im Pulverbettverfahren mittels Laserstrahl aufgeschmolzen und somit schichtweise aufgebaut. Das Verfahren findet bereits in der Luft- und Raumfahrt, der Medizintechnik, aber auch in der Automobilindustrie und im Maschinenbau Anwendung für Prototypen, Einzelanfertigungen oder Kleinstserien. Des Weiteren ermöglicht es auch die Herstellung von Werkstücken mit besonders hoher Komplexität, die mit spanenden Verfahren nicht herstellbar sind, und bietet dadurch neue Gestaltungsmöglichkeiten bei der Konstruktion. Innerhalb des Vortrags werden nach der Vorstellung des Verfahrens verschiedene Methoden zur numerischen Simulation des selektiven Laserschmelzens von Edelstahl (1.4404) am Beispiel der kommerziellen Software Simufact Additive erläutert. Dazu werden der mechanische und thermo-mechanische Lösungsansatz betrachtet sowie die Methode zur Kalibrierung der Simulationen erläutert. Die Erläuterung eines voll transienten thermo-mechanischen Ansatzes erfolgt unter Verwendung der Software MSC Marc. Des Weiteren wird der Einfluss der Orientierung des Werkstücks im Herstellungsprozess auf resultierende Spannungen, Verzug sowie mechanische Eigenschaften analysiert und mit experimentellen Untersuchungen untersetzt.

In our experience of teaching Calculus to engineering undergraduates we have had to grapple with many different problems. A major hurdle has been students’ inability to appreciate the importance of the theory. In their view the theoretical part of mathematics is separate from the computing part. In general, students also believe that they can pass their exams even though they do not have a real understanding of the theory behind the problems they are required to solve. In an effort to surmount these difficulties we tried to find ways to make students better understand the theoretical part of Calculus. This paper describes our experience of teaching Calculus. It reports on the continuation of our previous research.

Additive manufacturing (AM) is an attractive way to shorten development time, reduce product weight and allow the manufacturing of more complex products than by conventional manufacturing processes. The problem arises when the previous traditional manufacturing requirements need to be fulfilled by AM as well as the volume production capability. This investigation is done together with Ericsson to evaluate the possibilities of the different AM technologies, post-processing methods and silver coating processes to guarantee the specifications of radiofrequency (RF) filters. Here, minimal RF signal insertion losses are targeted. Since insertion losses are dependent on surface roughness, surface smoothness is sought as well. Ericsson simulation software uses correction factors to account for surface roughness, however there are some inconsistencies between the simulated and actual surface roughness that is allowed in the parts. In AM parts, surface roughness is not easy to control since it depends on parameters related to feedstock, process and machine properties. Commonly, most AM components do not comply with requirements of lower surface roughness values. Therefore, parts need to be smoothened before silver plated; this step is necessary to ensure the electrical conductivity in this specific application. These finishing processes add costs to the final product and increase time to market. Firstly, a comprehensive study was carried out to better understand the landscape of AM technologies, postprocessing and silver coating methods. Secondly, the different processes are assessed with the help of selection matrices, considering the products requirements. The components to print are two RF filters with different shapes and dimensions but similar requirements. The CAD design is modified depending on each AM process and directly affects the results. Afterwards, the design of an experimental plan is carried out; the number of samples of each part comparing AM technologies, feedstock, different suppliers (3D printing and post-processing) is obtained. Due to budget and time restrictions, the parts were printed using Multi Jet Fusion and Selective Laser Melting processes. After printing, tolerances and surface roughness were measured. This thesis results in the selection of suitable AM technologies and post-processing methods for RF filters. For MJF printed cavities at 0˚, 30˚ and 90˚ orientation, the best results for this application are obtained at 30˚ providing a good balance between sharp detail and smooth surfaces. In the case of SLM, waveguides are printed at 0˚ and 30˚. 30˚ waveguides present lower surface roughness values than the 0˚ ones as inner support material is needed at 0˚ orientation. SLM cavities were printed at 30˚ in seek of asymmetry between faces, resulting in higher surface roughness in the downfacing face.