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Ashton, I. "Investigations into process monitoring for selective laser melting." Thesis, University of Liverpool, 2016. http://livrepository.liverpool.ac.uk/3004532/.
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Suchý, Jan. "Zpracování vysokopevnostní hliníkové slitiny AlSi9Cu3 technologií selective laser melting." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2017. http://www.nusl.cz/ntk/nusl-319259.
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Method selective laser melting can produce metal parts by using 3D printing. This diploma thesis deals with the influence of process parameters on the workability of AlSi9Cu3 high-strength aluminum alloy using selective laser melting. The theoretical part deals with relations between process parameters and identifies phenomena occurring during the processing of metals by this technology. It also deals with conventionally manufactured aluminum alloy AlSi9Cu3. In the work, material research is performed from single tracks tests, porosity tests with different process parameters and mechanical testing. Here are showing the trends of porosity change at scanning speed, laser power, individual laser stop distance, bulk energy, and powder quality. The workability of the material can be judged by the degree of relative density achieved. Simultaneously the values of the achieved mechanical properties of the selected process parameters are presented. The data obtained are analyzed and compared with literature.
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Kurian, Sachin. "Process-Structure-Property Relationship Study of Selective Laser Melting using Molecular Dynamics." Thesis, Virginia Tech, 2020. http://hdl.handle.net/10919/104115.
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Selective Laser Melting (SLM), a laser-based Additive Manufacturing technique has appealed to the bio-medical, automotive, and aerospace industries due to its ability to fabricate geometrically complex parts with tailored properties and high-precision end-use products. The SLM processing parameters highly influence the part quality, microstructure, and mechanical properties. The process-structure-property relationship of the SLM process is not well-understood. In the process-structure study, a quasi-2D model of Micro-Selective Laser Melting process using molecular dynamics is developed to investigate the localized melting and solidification of a randomly-distributed Aluminum nano-powder bed. The rapid solidification in the meltpool reveals the cooling rate dependent homogeneous nucleation of equiaxed grains at the center of the meltpool. Long columnar grains that spread across three layers, equiaxed grains, nano-pores, twin boundaries, and stacking faults are observed in the final solidified nanostructure obtained after ten passes of the laser beam on three layers of Aluminum nano-powder particles. In the structure-property study, the mechanical deformation behavior of the complex cellular structures observed in the SLM-fabricated 316L Stainless Steel is investigated by performing a series of molecular dynamics simulations of uniaxial tension tests. The effects of compositional segregation of alloying elements, distribution of austenite and ferrite phases in the microstructure, subgranular cell sizes, and pre-existing (grown in) nano-twins on the tensile characteristics of the cellular structures are investigated. The highest yield strength is observed when the Nickel concentration in the cell boundary drops very low to form a ferritic phase in the cell boundary. Additionally, the subgranular cell size has an inverse relationship with mechanical strength, and the nano-twinned cells exhibit higher strength in comparison with twin-free cells.Master of Science
Additive Manufacturing's (AM) rise as a modern manufacturing paradigm has led to the proliferation in the number of materials that can be processed, reduction in the cost and time of manufacturing, and realization of complicated part geometries that were beyond the capabilities of conventional manufacturing. Selective Laser Melting (SLM) is a laser-based AM technique which can produce metallic parts from the fusion of a powder-bed. The SLM processing parameters greatly influence the part's quality, microstructure, and properties. The process-structure-property relationship of the SLM process is not well-understood. In-situ experimental investigation of the physical phenomena taking place during the SLM process is limited because of the very small length and time scales. Computational methods are cost-effective alternatives to the challenging experimental techniques. But, the continuum-based computational models are ineffective in modeling some of the important physical processes such as melting, nucleation and growth of grains during solidification, and the deformation mechanisms at the atomistic scale. Atomistic simulation is a powerful method that can offset the limitations of the continuum models in elucidating the underlying physics of the SLM process. In this work, the influence of the SLM process parameters on the microstructure of the Aluminum nano-powder particles undergoing μ-SLM processing and the mechanical deformation characteristics of the unique cellular structures observed in the SLM-fabricated 316L stainless steel are studied using molecular dynamics simulations. Ten passes of the laser beam on three layers of Aluminum nano-powder particles have unfolded the formation mechanisms of a complex microstructure associated with the SLM process. The study on the deformation mechanisms of 316L stainless steel has revealed the contribution of the cellular structures to its superior mechanical properties.
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Siva, Prasad Himani. "Selective Laser Melting of Ni-based Superalloys: High Speed Imaging and Process Optimisation." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-59857.
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Additive manufacturing is the process of joining or adding material to build an object from 3D model data. Selective Laser Melting (SLM) is an additive manufacturing technology that generates components layer by layer. Though it is already being used in the industry, some aspects are not very well understood. In this thesis, high speed imaging is used to gain new insights about the interaction of laser light with material. A number of parameter sets for high e ciency and good surface finish were found for a nickel based superalloy, HastelloyXTM. Three setups are discussed: single laser pulse interaction with powder, low speed SLM and high speed SLM. It was found, that in order to observe powder behaviour, a narrow bandwidth illumination source is necessary. The low speed SLM process was imaged clearly and revealed three stages of the process, i.e. powder redistribution, melting and drop incorporation. In contrast, the high speed process included vertical powder displacement. Influence of various process parameters is also discussed.
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Liu, Bochuan. "Further process understanding and prediction on selective laser melting of stainless steel 316L." Thesis, Loughborough University, 2013. https://dspace.lboro.ac.uk/2134/13550.
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Additive Manufacturing (AM) is a group of manufacturing technologies which are capable to produce 3D solid parts by adding successive layers of material. Parts are fabricated in an additive manner, layer by layer; and the geometric data can be taken from a CAD model directly. The main revolutionary aspect of AM is the ability of quickly producing complex geometries without the need of tooling, allowing for greater design freedom. As one of AM methods, Selective Laser Melting (SLM) is a process for producing metal parts with minimal subtractive post-processing required. It relies on the generation and distribution of laser generated heat to raise the temperature of a region of a powder bed to above the melting point. Due to high energy input to enable full melting of the powder bed materials, SLM is able to build fully dense metal parts without post heat treatment and other processing. Successful fabrications of parts by SLM require a comprehensive understanding of the main process controlling parameters such as energy input, powder bed properties and build conditions, as well as the microstructure formation procedure as it can strongly affect the final mechanical properties. It is valuable to control the parts' microstructure through controlling the process parameters to obtain acceptable mechanical properties for end-users. In the SLM process, microstructure characterisation strongly depends on the thermal history of the process. The temperature distribution in the building area can significantly influence the melting pool behaviour, solidification process and thermal mechanical properties of the parts. Therefore, it is important to have an accurate prediction of the temperature distribution history during the process. The aim of this research is to gain a better understanding of process control parameters in SLM process, and to develop a modelling methodology for the prediction of microstructure forming procedure. The research is comprised of an experiment and a finite element modelling part. Experimentation was carried out to understand the effect of each processing control parameters on the final part quality, and characterise the model inputs. Laser energy input, build conditions and powder bed properties were investigated. Samples were built and tested to gain the knowledge of the relationship between samples' density and mechanical properties and each process control factor. Heat transfer model inputs characterisation, such as defining and measuring the material properties, input loads and boundary conditions were also carried out via experiment. For the predictive modelling of microstructure, a methodology for predicting the temperature distribution history and temperature gradient history during the SLM process has been developed. Moving heat source and states variable material properties were studied and applied to the heat transfer model for reliable prediction. Multi-layers model were established to simulate the layer by layer process principles. Microstructure was predicted by simulated melting pool behaviour and the history of three dimensional temperature distribution and temperature gradient distribution. They were validated by relevant experiment examination and measurement.
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Zvoníček, Josef. "Vývoj procesních parametrů pro zpracování hliníkové slitiny AlSi7 technologií Selective Laser Melting." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2018. http://www.nusl.cz/ntk/nusl-444404.
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The diploma thesis deals with the study of the influence of process parameters of AlSi7Mg0.6 aluminum alloy processing using the additive technology Selective Laser Melting. The main objective is to clarify the influence of the individual process parameters on the resulting porosity of the material and its mechanical properties. The thesis deals with the current state of aluminum alloy processing in this way. The actual material research of the work is carried out in successive experiments from the welding test to the volume test with subsequent verification of the mechanical properties of the material. Material evaluation in the whole work is material porosity, stability of individual welds, hardness of the material and its mechanical properties. The results are compared with the literature.
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Robinson, Joseph. "Optimisation of the selective laser melting process for the production of hybrid orthopaedic devices." Thesis, University of Liverpool, 2014. http://livrepository.liverpool.ac.uk/18053/.
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This thesis details investigations of residual stress in selective laser melting (SLM). SLM is an Additive Manufacturing (AM) process that builds parts by melting consecutive powder layers using a fibre laser. Residual stresses caused by high thermal gradients create deformation leading to cracking of the final components. This deformation and cracking limits the geometries that can be built and the materials from which they can be manufactured using the process. Previous research on residual stresses has shown contradictory results mainly due to the differences in measurement methods, processing parameters and materials used. In order to address this shortcoming this study focused on the use of Titanium and its alloys for the production of medical devices. The residual stress in final components was measured using several methodologies: deflection, hole drilling and EDM cutting followed by FEA (the contour method). These measurement methods allowed the comparison of commercially available scanning strategies to be investigated. Results showed that the chequerboard technique commonly cited in the literature as reducing residual stress had little benefit over the use of more standard rastered vectors scanned orthogonally to the previous layer vectors. Using this suite of techniques the principal residual stress was determined to be parallel to the scan vectors, contradicting a number of previous studies. A simple finite element model was developed enabling the comparison of measured profiles with analytical results. This model was then extended to allow the evaluation of new techniques aimed at reducing the levels of residual stress. Further experimentation showed that the use of increased bed temperatures reduced the residual stress in components even at small increases in temperature. Hatch angle rotation as a method for increasing part quality was also tested. Eighteen angles, specifically chosen, using analytical models were investigated to define the optimum angle. No statistically significant difference was found in density, surface finish or strength for any of the tested angles. To minimise residual stress it was concluded that unidirectional scan vectors should be avoided and that there was little difference between the other rotation angles. In order to measure precisely when and where the residual stresses were generated in the process an experimental apparatus was designed which allowed in-situ measurements of stresses and provided an understanding of the transient stresses in components as they are built. This residual stress dynamometer (RSD) offered state of the art spatial and temporal resolution. This experimental equipment allowed the conclusions drawn from the previous post process techniques to be confirmed on a layer by layer manner SLM has also been shown to be a viable technique for the production of hybrid orthopaedic devices that encompass both porous and solid volumes, this work considered the effect that optimisations on the solid volume of the part, to remove residual stresses, would have on the porous volumes. Techniques were developed which made the porous structures less sensitive to part orientation through the removal of broken links at the surface. Further additional features where then added to improve the roughness of the surface to increase initial fixation of an implant.
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Wang, Xiqian. "Improving the microstructure, mechanical properties & process route in selective laser melting of nickel-superalloys." Thesis, University of Birmingham, 2017. http://etheses.bham.ac.uk//id/eprint/7671/.
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Selective Laser Melting (SLM) was used to develop a manufacturing route for high temperature aero-engine components from the Ni-superalloys CM247LC, focussing on improving the microstructure, mechanical properties, and processing route. A statistical design of experiments approach was applied to determine the optimum processing parameters leading to the least structural defects. High-speed imaging was used to observe the melt pool during SLM. Microstructural investigations showed that certain elements were selectively evaporated, then condensed in the form of particles. These were then re-incorporated within the build. Cracks and pores were found in SLM-processed samples and these were sometimes associated with these condensed particles. Residual stresses, developed within SLMprocessed samples, were measured using neutron diffraction, highlighting the role of the scanning strategy on the residual stress development. The solidification microstructures formed in SLM-processed samples were characterised using analytical scanning and transmission electron microscopy. Cells, with identical orientation and 700 nm in width containing a high density of very small γʹ (up to 20 nm), were observed. Cell boundaries and grain boundaries were found to contain high densities of dislocations, Hf/Ti/Ta/W-rich precipitates and γ/γʹ eutectic containing larger particles of γʹ up to about 50 nm. The cooling rate derived from the cell size was estimated at 106 K/s, but the cooling rate, derived from the size of γʹ within grains was estimated as 104 K/s based on Jominy end-quench test. SLM-processed samples also showed high yield strength due to their fine microstructures, alongside poor ductility resulting from the presence of cracks. Post-SLM heat treatments were used to reduce the extent of cracking and porosity by Hot Isostatic Pressing (HIPping) and also to promote the precipitation of γʹ. These treatments improve the ductility in vertically built samples, but the ductility in horizontally built samples remains low. Though SLM-processed samples subjected to post-processing heat treatments showed poor creep strength, this was improved by HIPping. A novel approach for netshape SLM/HIP processing was assessed for manufacturing a blisk using powder CM247LC or dual materials.
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Prehradná, Jana. "Úprava oxidačních vlastností TiAl intermetalik přetavováním povrchu v řízené atmosféře." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2014. http://www.nusl.cz/ntk/nusl-231717.
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Rešerše se zabývá teorií technologického způsobu zpracování materiálů, tzv. povrchového tavení. V první části rešerše je popsána samotná technologie a základní parametry ovlivňující proces tavení. Ve druhé části je uvedeno srování dvou základních typů laserů, a to Nd:YAG a CO2 laser. CO2 laser byl použit v případě našeho experimentu. Třetí část se zabývá vlastnostmi TiAl intermetalických slitin, především jejich fázemi -TiAl a -Ti3Al. Na závěr teoretické části je zmíněna oxidace TiAl intermetalických slitin. Experimentální část je věnována přetavování povrchu slitiny Ti-46Al-0,7Cr-0,1Si-7Nb-0,2Ni, a to v ochranné atmosféře dusíku. Tato část obsahuje výsledky několika experimentů, na jejichž základě bylo nutné stanovit potřebné parametry pro požadovaný proces tavení. Posledním krokem experimentu byla snaha o zvýšení hmotnosti vzorků v důsledku následné oxidace.
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Aris, Mohd Shiraz. "The development of active heat transfer enhancement devices from shape memory alloys in a selective laser melting process." Thesis, University of Liverpool, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.526785.
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Clucas, D. A. V. "A theoretical and experimental investigation into the variation of process parameters in the laser heating, melting and welding processes." Thesis, University of Liverpool, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366419.
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Fürstenau, Jan-Philipp [Verfasser], and Peter [Akademischer Betreuer] Wriggers. "Particle-based Simulation of the Selective Laser Melting Process : Partikelbasierte Simulation des selektiven Laserschmelzprozesses / Jan-Philipp Fürstenau ; Betreuer: Peter Wriggers." Hannover : Gottfried Wilhelm Leibniz Universität, 2020. http://d-nb.info/1233426427/34.
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Swartz, Paul. "Evaluation of Tensile Properties for Selective Laser Melted 316L Stainless Steel and the Influence of Inherent Process Features." DigitalCommons@CalPoly, 2019. https://digitalcommons.calpoly.edu/theses/2024.
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Optimal print parameters for additively manufacturing 316L stainless steel using selective laser melting (SLM) at Cal Poly had previously been identified. In order to further support the viability of the current settings, tensile material characteristics were needed. Furthermore, reliable performance of the as-printed material had to be demonstrated. Any influence on the static performance of parts in the as-printed condition inherent to the SLM manufacturing process itself needed to be identified. Tensile testing was conducted to determine the properties of material in the as-printed condition. So as to have confidence in the experimental results, other investigations were also conducted to validate previous assumptions. Stereological relative density measurements showed that the as-printed material exhibited relative density in excess of 99%. Optical dimensional analysis found that the as-printed tensile specimens met ASTM E8 dimensional requirements in 14 out of 15 parts inspected. Baseline tensile tests indicated that the yield stress of the as-printed material is 24% higher than a cold-rolled alternative, while still achieving comparable ductility. The location of a tensile specimen on the build plate during the print was not found to have a significant effect on its mechanical properties. Theoretical behavior of notched tensile specimens based on finite element models matched experimental behavior in the actual specimens. Unique fracture behavior was found in both the unnotched reference and the most severe notch after microscopic inspection, and a root cause was proposed. Finally, extrapolating from previous studies and observing that experimental results matched theoretical models, it was determined that features inherent to SLM parts were not detrimental to the static performance of the as-printed material.
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Kubrický, Jakub. "Optimalizace SLM procesu pro výrobu úsťového zařízení útočné pušky." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2017. http://www.nusl.cz/ntk/nusl-318753.
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The thesis deals with optimization of the manufacturing process of the muzzle device designed for assault rifle. The most common titanium alloy named Ti-6Al-4V was chosen for this task. The introduction summarizes previously existing types of muzzle devices and further describes the SLM technology with a special focus on titanium alloys processing. The optimization methods and their follow-up testing were designed according to theoretical knowledge that is summarized in the theoretical part of this work. Firstly, the aim was to describe the optimization of the manufacturing process with attention to preserving the relative density of the parts. Secondly, the mechanical properties of the parts that underwent different heat treatment were tested.The obtained data were then used to design and manufacture a muzzle device that underwent further testing in real condition afterwards.
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Soprani, Davide. "Influenza dei parametri di processo sulle proprietà di componenti stampati mediante tecnologia “Selective Laser Melting” in acciaio 316L." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amslaurea.unibo.it/20857/.
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In questa attività di tesi ci si è posti l’obbiettivo di rilevare l’influenza dei parametri di processo sulle proprietà di componenti stampati mediante tecnologia selective laser melting in acciaio inossidabile 316L.
Per poter ottenere migliori proprietà meccaniche dobbiamo ottimizzare i parametri di elaborazione, in particolare: potenza del laser, dimensioni dello spot, spessore di strato, distanza tra le tracce, velocità di scansione, preriscaldamento e strategia di scansione.
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Rivalta, Francesco. "Effect of the scanning strategy on the SLM produced 18Ni300 maraging steel." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020.
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The aim of the thesis has been to investigate the effect of the scanning strategy and the main process parameters on the final parts produced through Selective Laser Melting.
Selective laser melting (SLM) is the most common Powder Bed Fusion technology and it uses high energy laser to selectively melt pre-deposited powders.
The printed material is the 18Ni300 maraging steel, a low-carbon ultra-high strength steel whose properties derive from the presence of nickel-based intermetallic compounds. Thanks to their good weldability and the resistance to quench cracking, the maraging steels are good candidate materials to be produced through the SLM process.
Interestingly, the microstructure of the SLM produced parts is completely different from the one of the traditionally produced ones, depending not just on the material but also on the values of the process parameters used to print. So, it is necessary to study in-depth the characteristics of the printed parts.
Four prints have been carried out, keeping constant the volumetric energy density, the laser power and the layer thickness. The scan speed, the hatch spacing, the rotation between adjacent layers and the scan strategy have been changed. In particular, the “stripes”, the “chessboard” and the “hexagonal” strategies have been considered.
It has been found out that the hexagonal strategy always led to the biggest external diameter, to the lowest density and almost always to the highest roughness of the final parts. All these negative results were probably related to the longer time elapsing between the scan of two adjacent tracks compared to the other two strategies.
The results of the nano-hardness tests are not clearly showing which strategy performs better, probably because a too small portion of specimen has been considered for those tests.
Moreover, ANOVA analysis has been performed and it confirmed the primary importance of the scan strategy as process parameter.
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Pulcini, Andrea. "Verifiche dimensionali e previsione della qualità di componenti meccanici realizzati mediante processo additivo." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/16471/.
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Il presente elaborato di tesi è frutto dell’attività di tirocinio svolta presso l’azienda modenese HPE COXA che opera nel settore dei servizi per l’ingegneria. Più nello specifico, lo svolgimento del tirocinio è avvenuto nel recente centro Metal Additive: centro di ricerca sull’Additive Manufacturing nato nell'ottobre 2017 e tuttora in fase di sviluppo. L’attività è svolta nell'ambito di simulazione del processo di Selective Laser Melting (SLM), tramite software commerciale Msc Simufact.Additive. Lo scopo dell’attività è stato quello di rendere la simulazione il più possibile in linea con il comportamento reale dei pezzi stampati. Di base il software ha una buona previsione dei fenomeni distorsivi, scaturiti principalmente dai forti gradienti termici che si sviluppano durante il processo di SLM, ma la quantità numerica di questi fenomeni deve essere tarata tramite specifici parametri di processo. Proprio sulla taratura di questi parametri di processo è incentrato il lavoro svolto. La simulazione di processo si colloca a monte della stampa, come uno strumento utile alla previsione di eventuali criticità durante la stampa. Queste criticità nella maggior parte dei casi portano all'interruzione del processo di produzione, con conseguente perdita di materiale e tempo, di vitale importanza nel mondo industriale. La principale sfida che si pone davanti agli sviluppatori di software dedicati alla simulazione del processo di SLM è sicuramente il tempo di calcolo, poiché la natura microscopica dei fenomeni in gioco porta ad avere mesh nell'ordine dei decimi di millimetro. Dunque, senza una strategia o semplificazione a monte dell’impostazione del modello la simulazione non è fattibile, nemmeno con le più avanzate risorse hardware.
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Malý, Martin. "Experimentální komora pro testování speciálních materiálů technologií SLM." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2017. http://www.nusl.cz/ntk/nusl-318407.
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The thesis deals with the influence of process temperature and pressure on 3D printing using Selective Laser Melting. The aim of the thesis is the design, manufacture and testing of the experimental chamber for SLM 280HL from company SLM Solutions. The main task of the experimental chamber is to increase the temperature of the preheating of the powder bed from the original 200 °C to at least at 400 °C. The device will be used to investigate the influence of high process temperature on the properties of printed materials. The thesis also deals with the design of the powder applicator for elevated temperatures.
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Simonelli, Marco. "Microstructure evolution and mechanical properties of selective laser melted Ti-6Al-4V." Thesis, Loughborough University, 2014. https://dspace.lboro.ac.uk/2134/15070.
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Selective laser melting (SLM) has been shown to be an attractive manufacturing route for the production of ??/?? titanium alloys, and in particular Ti-6Al-4V. A thorough understanding of the relationship between the process, microstructure and mechanical properties of the components produced by this technology is however crucial for the establishment of SLM as an alternative manufacturing route. The purpose of the present study is thus to determine the microstructure evolution, crystallographic texture and the mechanical properties of SLM Ti-6Al-4V. The effect of several processing parameters on the density and the microstructure of the SLM samples were initially investigated. It was found that different sets of process parameters can be used to fabricate near fully dense components. It was found that the samples built using the optimised process window consist exclusively of ????? martensitic phase precipitated from prior ?? columnar grains. It was observed that the ?? grain solidification is influenced by the laser scan strategy and that the ?? phase has a strong <001> texture along its grain growth direction. The ????? martensitic laths that originate from the parent ?? grains precipitate according to the Burgers orientation relationship. It was found that ????? laths clusters from the same ?? grain have a specific misorientation that minimise the local shape strain. Texture inheritance across successive deposited layers was also observed and discussed in relation to various variant selection mechanisms. The mechanical properties of as-built and stress relieved SLM Ti-6Al-4V built using the same optimised process parameters were then investigated. It was found that the build orientation affects the tensile properties, and in particular the ductility of the samples. Samples built perpendicularly to the building direction showed higher ductility than those built in the vertical orientation. It was also observed that a stress relief heat treatment was beneficial to the mechanical properties of SLM Ti-6Al-4V. The ductility of the stress relieved samples was indeed higher than those found in the as-built condition. It was found that the predominant fracture mode during tensile testing is inter-granular. In terms of high-cycle fatigue, it was found that SLM Ti-6Al-4V is comparable to HIPed cast Ti-6Al-4V but it has a significantly lower fatigue resistance than that of wrought and annealed alloys. It was observed that porosity and the elongated prior ?? grain boundaries decrease substantially the fatigue life of the components. Cracks propagate either by fatigue striation or ductile tearing mechanisms. Using alternative laser scan strategies it was possible to control the microstructure of the as-built samples. It was observed that the laser scan vector length influences several microstructural features, such as the width of the prior ?? grains and the thickness of the ????? laths. It was found that re-melting the same layer has instead little effect on the microstructure. A novel laser scan strategy characterised by much lower laser power and scan speed than those typically used in SLM enabled finally to fabricate SLM Ti-6Al-4V with a microstructure close to that of conventionally manufactured Ti-6Al-4V. This study investigates for the first time the crystallographic texture evolution in Ti-6Al-4V manufactured by SLM. Further, this research presents for the first time the effect of the characteristic microstructure and crystallographic texture on the mechanical properties and fracture of SLM Ti-6Al-4V. Lastly, for the first time this research shows examples of microstructural control during the SLM fabrication of the same alloy using long laser dwell times.
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Davis, Taylor Matthew. "Feasibility and Impact of Liquid/Liquid-encased Dopants as Method of Composition Control in Laser Powder Bed Fusion." BYU ScholarsArchive, 2021. https://scholarsarchive.byu.edu/etd/9256.
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Additive manufacturing (AM) – and laser powder bed fusion (LPBF) specifically – constructs geometry that would not be possible using standard manufacturing techniques. This geometric versatility allows integration of multiple components into a single part. While this practice can reduce weight and part count, there are also serious drawbacks. One is that the LPBF process can only build parts with a single material. This limitation generally results in over-designing some areas of the part to compensate for the compromise in material choice. Over-designing can lead to decreased functional efficiency, increased weight, etc. in LPBF parts. Methods to control the material composition spatially throughout a build would allow designers to experience the full benefits of functionality integration. Spatial composition control has been performed successfully in other AM processes – like directed energy deposition and material jetting – however, these processes are limited compared to LPBF in terms of material properties and can have inferior spatial resolution. This capability applied to the LPBF process would extend manufacturing abilities beyond what any of these AM processes can currently produce. A novel concept for spatial composition control – currently under development at Brigham Young University – utilizes liquid or liquid-encased dopants to selectively alter the composition of the powder bed, which is then fused with the substrate to form a solid part. This work is focused on evaluating the feasibility and usefulness of this novel composition control process. To do this, the present work evaluates two deposition methods that could be used; explores and maps the laser parameter process space for zirconia-doped SS 316L; and investigates the incorporation of zirconia dopant into SS 316L melt pools. In evaluating deposition methods, inkjet printing is recommended to be implemented as it performs better than direct write material extrusion in every assessed category. For the process space, the range of input parameters over which balling occurred expanded dramatically with the addition of zirconia dopant and shifted with changes in dopant input quantities. This suggests the need for composition-dependent adjustments to processing parameters in order to obtain desired properties in fused parts. Substantial amounts of dopant material were confirmed to be incorporated into the laser-fused melt tracks. Individual inclusions of 100 $nm$ particles distributed throughout the melt pool in SEM images. Howewver, EDX data shows that the majority of the incorporated dopant material is located around the edges of the melt pools. Variations of dopant deposition, drying, and laser scanning parameters should be studied to improve the resulting dopant incorporation and dispersion in single-track line scans. Area scans and multi-layer builds should also be performed to evaluate their effect on dopant content and dispersion in the fused region.
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Berglund, Lina, Filip Ivarsson, and Marcus Rostmark. "Crucial Parameters for Additive Manufacturing of Metals : A Study in Quality Improvement." Thesis, KTH, Skolan för industriell teknik och management (ITM), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-254785.
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Production by Additive Manufacturing creates opportunities to make customized products in small batches with less material than in traditional manufacturing. It is more sustainable and suitable for niche products, but entails new production demands to ensure quality. The goal of this study is to define the most crucial parameters when creating Additive Manufactured products in metal and suggest tools for quality improvement. This is done by analysing earlier studies and evaluating the standard production procedures for manufacturing by Selective Laser Melting. The results from this study stated that porosity and insufficiencies in shape are the most common factors leading to deviation in quality. To avoid it, the most crucial parameters to consider are; The laser freeform fabrication-system related parameters, hatch distance, laser power, layer thickness, fscanning pattern, scan speed and flowability of the powder. Concluded is also that crucial parameters within additive manufacturing are very dependent on the definition of quality for a certain product and can therefore vary. By continuous collection and analysis of data, the task of improving quality will be simplified.Produktion genom Additiv Tillverkning möjliggör tillverkande av skräddarsydda produkter i små batcher och med mindre material än vid traditionell tillverkning. Det är ett mer hållbart tillverkningssätt och mer passande för nischprodukter, men innebär nya produktionskrav för att säkerhetsställa bra kvalitet. Målet med denna studie är att definiera de viktigaste parametrarna vid Additiv Tillverkning av produkter i metall och föreslå verktyg för att förbättra dem. Detta genom analys av tidigare studier och utvärdering av klassiska produktionsrutiner för Selective Laser Melting. Resultaten från denna studie visar att porositet och formfel är de vanligaste faktorerna som leder till bristande kvalitet. För att undvika detta är de viktigaste parametrarna att ta i beaktande; parametrar kopplade till "laser freeform fabrication"-system, distans mellan laserstrålar, kraft på lasern, lagertjocklek, skanningsmönster, fart på skanningen och flytbarhet på pulvret. Slutsatsen pekar även på att avgörande parametrar inom Additiv Tillverkning beror på definitionen av kvalitet för en speciell produkt och kan därför variera. Genom kontinuerlig insamling och analys av data kommer förbättringen av kvalitet förenklas markant.
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Těšický, Lukáš. "Optimalizace parametrů SLM procesu při zpracování hliníkové slitiny AW2618." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2017. http://www.nusl.cz/ntk/nusl-318646.
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The diploma thesis deals with possibilities for processing aluminium alloy EN AW 2618 using Selective laser melting (SLM). The theoretical part contains basic knowledge about production by this technology and possibilities of evaluation of relative density of samples. It also contains an overview of the current state of knowledge about the processing of aluminium alloys by SLM technology. Above all, aluminium alloys of the series 2000, where the main alloying element is copper. In the experimental part testing samples were designed based on the research. These samples can be divided into three areas: single-track specimens, volume samples and samples for tensile testing. Single-track and volume samples were used to find appropriate processing parameters to achieve a relative density close to full volume of material. For this purpose, the effect of the different scanning strategies on the relative density of the sample were examined. The limiting factor has been the occurrence of small cracks in the broad range of parameters studied. Mechanical properties of samples produced by SLM were compared with extruded material. It was found that the material processed by SLM achieves only half the yield strength and tensile strength of extruded material. This is mainly due to the occurrence of small cracks and other defects in the structure of the material.
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Doubrava, Marek. "Mechanické vlastnosti materiálů připravovaných pomocí procesu SLM." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2019. http://www.nusl.cz/ntk/nusl-400835.
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The diploma thesis deals with the selection of process parameters used for manufacturing of high-strenth materials using SLM technology. The feedstock material was powder with a chemical composition according to standard DIN X3NiCoMoTi 18-9-5. Influence of change in process parameters on mechanical properties was examined by hardness tests and tensile tests. Metallographic and fractographic analysis were conducted with an aim to understand mechanisms of failure present in this type of material. Selection of optimal process parameters was based on the analysis of mechanical properties of manufactured samples. Possible future steps related to the improvement of the process were proposed. Results of this experiment were compared with literature regarding parts produced by SLM technology and conventional methods.
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Hyspecká, Klára. "Mechanické vlastnosti materiálů připravovaných pomocí procesu SLM." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2019. http://www.nusl.cz/ntk/nusl-400836.
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The final thesis determined the properties of alloys formed from mixtures of powders processed by the SLM method. Powders of alloy AlSi12 and EN AW 2618 were fused in the proportion 75 wt. % AlSi12 + 25 wt. % 2618, 50 wt. % AlSi12 + 50 wt. % 2618 and 25 wt. % AlSi12 + 75 wt. % 2618. Metallographic analysis, EBSD analysis and line EDS microanalysis were made on the samples. Tensile test at room temperature and hardness were carried out to determine the mechanical properties. Fractographic analysis was performed after tensile test.
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Vitásek, Ladislav. "Mechanické vlastnosti Al slitiny připravené pomocí procesu SLM." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2017. http://www.nusl.cz/ntk/nusl-319620.
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The master's thesis deals with properties of aluminium alloys prepared by SLM process. The teoretical part of thesis is focused on decribtion of selective laser melting technology, metallurgical defects and mechanical properties of aluminium alloys processed by this technology. The experimental part of this thesis deals with selections of the SLM process parameters suitable for samples preparation in bulk. Tensile testing at room temperature was used for evaluation of basic mechanical properties. Metallographic and fractographic analyses were performed for evaluation of the microstructure and fracture mechanisms. The materials characteristics obtained on SLM samples were compared with the properties of the same materials grade produced by conventional technologies.
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Masmoudi, Amal. "Modélisation et développement expérimental du procédé de fabrication additive par fusion laser sélective d'un lit de poudre métallique : influence de la pression de l'atmosphère." Thesis, Belfort-Montbéliard, 2016. http://www.theses.fr/2016BELF0287/document.
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Le procédé de fusion sélective par laser (SLM) d’un lit de poudre métallique, est un procédé de fabrication additive qui permet de fabriquer des pièces de forme complexe directement à partir d’un fichier CAO en passant par la fusion totale de couches de poudre déposées successivement. Au cours du procédé SLM l’apport d’énergie du laser à la cible engendre de nombreux cycles thermiques: fusion – vaporisation – solidification. Dans ce contexte, cette thèse a pour double objectif :1) une meilleure caractérisation et compréhension des phénomènes qui se produisent lors de l’interaction du faisceau laser avec la poudre et le bain de métal fondu à l’aide d’essais et 2) le développement d’un modèle numérique prenant en compte les phénomènes de fusion et de vaporisation de la matière ainsi que à la présence du gaz environnant à l’intérieur de la chambre de fabrication.Dans un premier temps, en considérant des géométries simples (cordons et surfaces) en acier inoxydable 316L, on a étudié l’interaction faisceau laser - lit de poudre / bain liquide métallique par différentes méthodes de diagnostics (spectrométrie, calorimètre, …) pour comprendre la nature et le rôle de la vapeur métallique générée au cours du procédé. Les résultats ont montré que cette vapeur est sans effet sur la transmission de l’énergie du laser à la matière au cours du procédé SLM. Par contre, elle conduit à la formation de condensats et peut aussi entrainer des gouttelettes de métal fondu.Ces analyses ont permis, dans un second temps, de développer un modèle numérique qui a pour objectif principal de caractériser l’influence de la pression du milieu environnant sur le processus de fusion du lit de poudre par le faisceau laser. Des paramètres caractérisant l’évolution des propriétés physiques du matériau et du milieu gazeux en fonction de la température et de la pression ont été intégrés dans les bases de données du modèle. Ces paramètres physiques du matériau ont été déterminés à partir de la littérature et d’autres ont été obtenus empiriquement à l’aide de mesures expérimentales spécifiques.Ce modèle numérique a été utilisé pour traiter le sujet principal de la thèse, à savoir celui de l’effet de la pression. Le modèle a permis de préciser les phénomènes physiques inhérents à la variation de la pression. Des manipulations expérimentales ont permis de vérifier la pertinence des données du modèle numérique proposéThe selective laser melting process (SLM) of a metallic powder bed is an innovative process that allows the manufacturing of complex shape parts directly from a CAD file via a complete melting of powder layers deposited successively. During the SLM process, the high laser energy density creates many thermal cycles: melting - vaporization - solidification.The purpose of this work was: 1) to better characterize and understand experimentally the phenomena that occur during the laser beam - powder / molten metal pool interaction and 2) to develop a numerical model taking into account the phenomena of melting and vaporizing of the material and the presence of the surrounding gas in the build chamber.In a first time, considering simple geometries (tracks and surfaces) and 316L stainless steel as material, we studied the interaction between the laser beam, the powder bed and the liquid metal pool using several experimental techniques (spectrometry, calorimetry, ...) in order to understand the nature and the role of the metal vapor generated during the process. The results showed that the vapor has no effect on the transmission of the laser beam energy to the material during the SLM process. Meanwhile it leads to the deposition of condensed vapor and also drag some molten metal droplets.In a second time a numerical model was developed to determine the influence of the pressure of the surrounding environment on the melting process of a powder bed by a laser beam. Parameters characterizing the evolution of the physical properties of the material and of the gaseous medium according to the temperature and pressure were incorporated into the model database. Some material parameters were determined from the literature and others were obtained empirically using specific experimental measurements.Finally, this numerical model, complementing experimental results, was used to treat the main subject of the thesis which is the effect of the surrounding pressure on the SLM process. The model helped to clarify the physical phenomena provided by the change in the pressure level and its validity was checked through experimental measurements
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Vašáková, Kristýna. "Mechanické vlastnosti materiálů připravovaných pomocí procesu SLM." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2019. http://www.nusl.cz/ntk/nusl-400837.
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This diploma thesis deals with properties of multi-materials interface composed of pure iron and Cu7Ni2Si1Cr alloy produced by SLM process. The theoretical part of thesis is focused on selective laser melting technology, and on description of defects connected with the production of SLM parts. Furthermore, one section deals with the production of multi-materials prepared by the SLM process. The experimental part of this thesis deals with selections of the SLM process parameters appropriate for bulk samples preparation. Mechanical properties were determined by the tensile tests at room temperature. Metallographic and fractographic analyses were performed for evaluation of the microstructure and description of the fracture mechanisms.
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Conti, Alfredo. "Tecniche della manifattura additiva - applicazioni in ambito aeronautico e aerospaziale." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2017. http://amslaurea.unibo.it/13306/.
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Il potenziale delle nuove tecnologie digitali applicate al settore industriale ha consentito di ridurre enormemente la durata dei cicli produttivi grazie alla rapida gestione di quantità di dati sempre più considerevoli attraverso l’introduzione delle Macchine a Controllo Numerico (Computer Numerical Control – CNC).
Nel corso delle ultime tre decadi, l’industria manifatturiera ha subito notevoli e sostanziali cambiamenti grazie ad una sempre più forte connessione con il mondo dell’informatica.
La più grande rivoluzione in tale ambito è stata segnata dall’avvento della Manifattura Additiva (Additive Manufacturing - AM), conosciuta sotto diversi nomi, tra i quali Prototipazione Rapida (Rapid Prototyping), Manifattura Rapida (Rapid Manufacturing) o Libera Fabbricazione di Forme (Free Form Fabrication).
Materia di ricerca e sviluppo sin dalla fine degli anni ’80, la Manifattura Additiva consente la creazione di elementi fisici tridimensionali partendo da modelli CAD attraverso la sovrapposizione successiva di materiale strato per strato (layer by layer), offrendo i benefici di una elevata flessibilità geometrica degli elaborati, altrimenti irraggiungibile attraverso le tradizionali tecniche di Manifattura Sottrattiva operanti per asportazione di materiale. In seguito ad intensive ricerche, progressi significativi sono stati fatti nello sviluppo e nella commercializzazione di nuovi ed innovativi processi AM.
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Zhang, Yanjun. "Scrap melting in a continuous process rotary melting furnace." Thesis, University of British Columbia, 2007. http://hdl.handle.net/2429/31195.
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Based on the preliminary modeling study, an improved heat-transfer model has been developed in this study to further examine the viability of the oxy-fuel-fired continuous process rotary melting furnace (CPRMF) as a replacement of the electric arc furnace (EAF) in minimill steelmaking. The model treats the furnace as three domains: the freeboard space, the liquid metal bath and slag, and the refractory structure. Based on certain physical correct assumptions for the gas flow and combustion patterns, radiative exchange within the freeboard is solved by the zone method in combination with a clear-plus-3-gray emissivity/absorptivity model for the gas phase thus the model allows axial temperature variations in the gas phase and the refractory hot-face. Assuming an isothermal metal bath condition, heat transfer to the exposed bath is simplified by a specified temperature difference between the slag/freeboard and slag/metal interfaces, while regenerative heat transfer to the covered bath is calculated using the local refractory temperature and the local heat-transfer coefficients. The refractory structure is solved by 1-D transient conduction in the radial direction. The three domains are linked by shared boundary conditions and the requirement that the furnace itself operates at steady-state. The model was partially validated using experimental results from copper melting trials on a bench-scale CPRMF, which was designed and constructed as a part of work in this study. The trials explored two operating variables, i.e., oxygen and slag. Both experimental and model results indicate an increase in furnace thermal efficiency with increasing oxygen enrichment in the combustion air and a decrease in the efficiency with increasing slag thickness. The partially validated model was then employed to evaluate the commercial viability of the CPRMF. According to the model predictions, a melting rate in the order of 100 ton h⁻¹ can be achieved by a 4 m ID x 16 m furnace with a natural gas firing rate of 6000 Nm³ h⁻¹. Under the baseline conditions, the furnace thermal efficiency is 66%. Without scrap preheating, this configuration consumes less direct energy at 619 kWh t⁻¹ than the typical EAF (662 kWh t⁻¹) and can save at-source energy by about 45%.Applied Science, Faculty of
Materials Engineering, Department of
Graduate
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Prashanth, Konda Gokuldoss. "Selective laser melting of Al-12Si." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-144245.
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Selective laser melting (SLM) is a powder-based additive manufacturing technique consisting of the exact reproduction of a three dimensional computer model (generally a computer-aided design CAD file or a computer tomography CT scan) through an additive layer-by-layer strategy. Because of the high degree of freedom offered by the additive manufacturing, parts having almost any possible geometry can be produced by SLM. More specifically, with this process it is possible to build parts with extremely complex shapes and geometries that would otherwise be difficult or impossible to produce using conventional subtractive manufacturing processes. Another major advantage of SLM compared to conventional techniques is the fast cooling rate during the process. This permits the production of bulk materials with very fine microstructures and improved mechanical properties or even bulk metallic glasses. In addition, this technology gives the opportunity to produce ready-to-use parts with minimized need for post-processing (only surface polishing might be required). Recently, significant research activity has been focused on SLM processing of different metallic materials, including steels, Ti-, Ni- and Al-based alloys. However, most of the research is devoted to the parameters optimization or to feasibility studies on the production of complex structures with no detailed investigations of the structure-property correlation.
Accordingly, this thesis focuses on the production and structure-property correlation of Al-12Si samples produced by SLM from gas atomized powders. The microstructure of the as-prepared SLM samples consists of supersaturated primary Al with an extremely fine cellular structure along with the residual free Si situated at the cellular boundaries. This microstructure leads to a remarkable mechanical behavior: the yield and tensile strengths of the SLM samples are respectively four and two times higher than their cast counterparts. However, the ductility is significantly reduced compared with the cast samples. The effect of annealing at different temperatures on the microstructure and resulting mechanical properties of the SLM parts has been systematically studied by analyzing the size, morphology and distribution of the phases. In addition, the mechanical properties of the SLM samples have been modeled using micro- structural features, such as the crystallite and matrix ligament sizes. The results demonstrate that the mechanical behavior of the Al-12Si SLM samples can be tuned within a wide range of strength and ductility through the use of the proper annealing treatment.
The Al-Si alloys are generally used as pistons or cylinder liners in automotive applications. This requires good wear resistance and sufficient strength at the operating temperature, which ranges between 373 – 473 K. Accordingly, the tensile properties of the SLM samples were also tested at these temperatures. Changing the hatch style during SLM processing vary the texture in the material. Hence, samples with different hatch styles were produced and the effect of texture on their mechanical behavior was evaluated. The results show that the hatch style strongly influences both the mechanical properties and the texture of the samples; however no direct correlation was observed between texture and mechanical properties. The wear properties of the Al-12Si material was evaluated using pin-on-disc and fretting wear experiments. These experiments show that the as-prepared SLM samples exhibit better wear resistance than their cast counterparts and the SLM heat-treated samples. Finally, the corrosion investigations reveal that the SLM samples have similar corrosion behavior as the cast specimens under acidic conditions.
A major drawback for the wide application of SLM as an industrial processing route is the limited size of the products. This is a direct consequence of the limited dimensions of the available building chambers, which allow for the production of samples with volumes of about 0.02 m3. A possible way to overcome this problem would be the use of the welding processes to join the small SLM objects to form parts with no dimensional limitations. In order to verify this possibility, friction welding was employed to join Al-12Si SLM parts. The results indicate that friction welding not only successfully permits the join materials manufactured by SLM, but also helps to significantly improve their ductility.
This work clearly demonstrates that SLM can be successfully used for the production of Al-12Si parts with an overall superior performance of the mechanical and physical properties with respect to the conventional cast samples. Moreover, the mechanical properties of the SLM samples can be widely tuned in-situ by employing suitable hatch styles or ex-situ by the proper heat treatment. This might help the development of SLM for the production of innovative high-performance Al-based materials and structures with controlled properties for automotive and aerospace applications.
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Lamb, M. "Laser surface melting of stainless steel." Thesis, Imperial College London, 1985. http://hdl.handle.net/10044/1/37753.
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Otsu, David Takeo. "Preliminary Investigations into Selective Laser Melting." DigitalCommons@CalPoly, 2017. https://digitalcommons.calpoly.edu/theses/1758.
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Selective laser melting is a promising metallic additive manufacturing process with many potential applications in a variety of industries. Through a gracious donation made by Lawrence Livermore National Laboratory, California Polytechnic State University received and installed an SLM 125 HL selective laser melting machine in February 2017. As part of the initial setup effort, a preliminary machine verification study was conducted to evaluate the general print quality of the machine with default parameter settings. Coincidentally, the as-printed microstructure of SLM components was evaluated through nil strength fracture surface examination, an alternative to conventional polish-and-etch metallography. A diverse set of components were printed on the SLM 125 HL to determine the procedural best practices and inherent constraints. Additionally, the mode and mechanism of failure for a defective Lawrence Livermore National Laboratory component fabricated at their facility was investigated. From these studies, extensive documentation in the form of standard operating procedures, guidelines, templates, and summary reports was generated with the intent of facilitating future selective laser melting research at Cal Poly and strengthening the learning of students interfacing with the novel technology.
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Foster, Moira. "Defect Detection in Selective Laser Melting." DigitalCommons@CalPoly, 2018. https://digitalcommons.calpoly.edu/theses/1874.
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Additively manufactured parts produced using selective laser melting (SLM) are prone to defects created during the build process due to part shrinkage while cooling. Currently defects are found only after the part is removed from the printer. To determine whether cracks can be detected before a print is completed, this project developed print parameters to print a test coupon with inherent defects – warpage and cracking. Data recorded during the build was then characterized to determine when the defects occurred.
The test coupon was printed using two sets of print parameters developed to control the severity of warpage and cracking. The builds were monitored using an accelerometer recording at 12500 samples per second, an iphone recording audio at 48000 samples a second, and a camera taking a photo every build layer. Data was analyzed using image comparison, signal amplitude, Fourier Transform, and Wavelet Decomposition.
The developed print parameters reduced warpage in the part by better distributing heat throughout the build envelope. Reducing warpage enabled the lower portion of the part to be printed intact, preserving it to experience cracking later in the build. From physical evidence on the part as well as time stamps from the machine script, several high energy impulse events in the accelerometer data were determined to be when cracking occurred in the build. This project’s preliminary investigation of accelerometers to detect defects in selective laser melting will be used in future work to create machine learning algorithms that would control the machine in real time and address defects as they arise.
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Buchbinder, Damien [Verfasser]. "Selective Laser Melting von Aluminiumgusslegierungen / Damien Buchbinder." Aachen : Shaker, 2013. http://d-nb.info/104938167X/34.
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Khan, Mushtaq. "Selective Laser Melting (SLM) of gold (Au)." Thesis, Loughborough University, 2010. https://dspace.lboro.ac.uk/2134/6163.
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Selective Laser Melting (SLM) is a laser based Solid Freeform Fabrication (SFF process which uses laser energy to melt a thin layer of metal powder. This process is repeated to produce a 3-dimensional metallic part. SLM is capable of producing intricate parts which are otherwise difficult to produce with conventional manufacturing techniques. As compared to traditional manufacturing processes, SLM can also produce parts with higher density. Before a material is processed using SLM, suitable processing parameters are first identified. Over the years, different materials have been processed using the SLM process. However, very little work has been done on SLM of bio-compatible precious metals such as gold and its alloys. Gold and its alloys have been used for manufacturing of dental crowns for centuries. The SLM process could be used to produce intricate metallic substructures for porcelain fused to metal dental restorations. This research work was focused on understanding the processing parameters for SLM of 24 carat gold powder. The gold powder was analyzed for Particle Size Distribution (PSD), apparent density and tap density before identifying suitable processing parameters for SLM. The gold powder particles were found to be spherical in nature but smaller particles stuck to each other and formed larger powder agglomerates. From the apparentdensity experiments, the gold powder was found to be cohesive and non-flowing in nature which hindered powder flowability during the powder deposition process with the existing system. This issue was resolved by designing a new powder deposition system which could allow the gold powder to flow evenly over the substrate. The tap density of the gold powder was found by Constant Weight Tap Density (CWTD) and Constant Volume Tap Density (CVTD) techniques. The difference in results from these two techniques was negligible. Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) of gold powder showed it to be more than twice as reflective as other commonly processed metal powders such as stainless steel and H13 tool steel. This analysis proved useful in understanding the laser processing of gold powder. Due to the high cost and small quantity of material available for this work, a very small build platform was designed to optimise material utilisation and reduce wastage. Single scans were performed on a single layer of gold powder to identify the good melting region. Five different regions i.e. balling, good melting, unstable melt, weak sintering and very little sintering were observed in the processing window. The balling phenomenon was observed at low and high scan speeds, which was due to the melt pool instability at these parameter settings. The size of droplets (balling) also increased with decreasing scan speed and increasing laser power which was due to an increase in the break up time of the molten metal. In the good melting region, the gold powder was found to be completely melted and continuous beads were successfully produced. The unstable melt region showed the melt pool spreading unevenly in different directions whereas in the weak sintering and very little sintering regions the gold powder did not melt completely. Single layers were produced on a layer of gold powder, which showed the parameters in the good melting regions to be suitable for multiple layer parts manufacturing. Gold cubes were produced using the suitable processing parameters identified from single scan and single layer experiments and then analyzed for their internal porosity. The porosity in the gold cubes was found to be at a minimum for parameters obtained in the good melting region. The internal porosity was found to be mostly inter-layer porosity; this indicated less heat transferred to the region between the two layers which could be associated with the high reflectivity of gold. The inter-layer porosity in gold cubes was further reduced by reducing the layer thickness. This could be due to the thinner layers requiring less energy to melt and be fused to the previous layers. The hatch distance had a negligible effect on the inter-layer porosity of gold cubes. The reduction in hatch distance increased the energy delivered but it was still not enough to completely melt the gold powder and fuse it to the previous layer. A pre-scan technique was also tested to be used for pre-heating the powder bed. However, due to the rapid drop in temperature, this technique was not found suitable to be used as a powder bed pre-heating technique. The gold cubes were checked for their mechanical properties i.e. hardness and modulus. The hardness of gold cubes was found to be higher than expected for 24 carat gold. The modulus was found to be less than 24 carat gold. This variation in the mechanical properties of gold cubes could be due to the rapid heating and cooling of material during the laser processing or presence of internal porosity in these gold cubes. After single scans and single layers manufacturing, gold dental parts (premolar and molar) were also manufactured using the optimum processing parameters. These gold dental parts were also analyzed for their internal porosity, which was found to be less than that observed in gold cubes. This difference in porosity could be due to the difference in structure of gold cubes and premolar part, where the latter was a thin wall structure.
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Tsopanos, Sozon. "Micro Heat Exchangers by Selective Laser Melting." Thesis, University of Liverpool, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.507633.
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Selective Laser Melting (SLM), a layer-based Solid Freeform Fabrication (SFF) process, was used to fabricate micro cross-flow heat exchangers from 316L stainless steel, bronze (Cu 90%, Sn 10%) and Inconel 718 powder. Their mechanical and thermal properties were determined using solid blocks of SLM material prior to the fabrication of the micro cross flow heat exchangers. Initially the process parameters for the fabrication of high density (>97%) parts for the different materials were defined. The mechanical and thermal properties of SLM parts were then measured. The tensile test results exhibited yield strength values superior to the parent metals, but also showed low tensile strength and ductility as a result of the inherent residual porosity (2-4%). Results obtained from the thermal conductivity of the stainless steel material system were in good agreement with the bulk material values. The heat transfer performance of the heat exchangers with either micro channels or lattice structures as heat exchange surfaces was investigated experimentally and the results were evaluated in terms of geometry and materials. The performance of the micro heat exchangers was found to be dependent not only on the choice of material but also on the heat exchanger media geometry.
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Fateri, Miranda [Verfasser]. "Selective Laser Melting of Glass Powders / Miranda Fateri." München : Verlag Dr. Hut, 2018. http://d-nb.info/1155056159/34.
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Parry, Luke Alexander. "Investigation of residual stress in selective laser melting." Thesis, University of Nottingham, 2018. http://eprints.nottingham.ac.uk/48964/.
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Selective laser melting is an attractive technology, enabling the manufacture of customised, complex metallic designs, with minimal wastage. However, uptake by industry is currently impeded by several technical barriers, such as the control of residual stress, which have a detrimental effect on the manufacturability and integrity of a component. Indirectly, these impose severe design restrictions and reduce the reliability of components, driving up costs. This thesis documents work on investigating the generation of residual stresses created in the selective laser melting process by the use of a finite element thermo-mechanical model. The thermo-mechanical model incorporated an adaptive meshing strategy which was used in conjunction with the use of high performance computing facilities. These together significantly increased the computational throughput for simulating selective laser melting of a single layer. Additionally, a volumetric hatching method was created to generate the laser scan vectors used in the process, with the ability to both simulate and manufacture on selective laser melting machines. A number of studies were performed to better understand the effect of laser scan strategy on the generation of residual stress in selective laser melting. Using this model, a series of investigations were performed to understand the effect of scan strategy and scan area size on the generation of residual stress in this process. Further studies were also performed to investigate the role of laser parameters, geometry, and support structures in selective laser melting and their effect on the generation of residual stress. The studies showed a complex interaction between transient thermal history and the build-up of residual stress has been observed in two conventional laser scan strategies (unidirectional and alternating) investigated. The temperature gradient mechanism was discovered for the creation of residual stress and the scan area size had an effect on the temperature sustained within the region. The parametric study of the laser parameters showed that an increase in laser scan speed increased the melt pool aspect ratio, and increase in laser power increased the melt pool width. The parametric thermo-mechanical analysis revealed that the laser scan speed had the most influence on the magnitude and anisotropy of the residual stresses generated. Varying the hatch distance had little effect on the maximum magnitude of residual stresses generated, but decreasing the hatch distance significantly increased the level of yielding that occurred. A study of the geometrical effect on scan strategy revealed the importance of the thermal history on the transverse stresses generated, influenced by the arrangement of scan vectors. The higher magnitude longitudinal stresses had predictable behaviour; only dependent on the scan vector length and not the thermal history generated by the choice of laser scan geometry. It was shown that the laser scan strategy becomes less important for scan vector length beyond the typical 5 mm island sizes. From the study of the support structures, it was found the insulating properties of the metal powder used in selective laser melting provide a significant thermal resistance for the dissipation of heat, and caused uniform overheating across the scanned region. In particular, the analysis showed localised overheating using support structures, which affected the melt pool geometry, and the residual stresses generated due to resistance against dissipating heat. Additionally, lattice structures such as the double gyroid showed localised overheating occurs using repeated exposures of short scan vectors. Suitable scan strategies therefore need to be developed to account for support structures. A multi-scale methodology was developed by combining information from the meso -scale obtained from the thermo-mechanical model. This model was used to predict the mechanical response of amacro -scale part. This approach used the assumption that meso -scale regions in island scan strategies behave independently from each other. This assumption was verified by comparing with a thermo-mechanical analysis. This multi-scale method was applied to a 3D structure and also to a complex 2D geometrical shape. Performing the multi-scale analyses has verified that the proposed technique of superposition of meso-scale stress fields at the macro -scale is a valid technique. The main strengths of the proposed multi-scale method is the decoupling of the meso and macro scale analyses. This has the benefit of reducing computational cost of the macro -scale analysis because it is independent of the complexity of the meso -scale analysis, and only requires performing once. These strengths translate into large computational time savings and also great flexibility in the physics incorporated at each scale.
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Dokoupil, Filip. "Zpracování slitiny 2618 pomocí technologie selective laser melting." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2015. http://www.nusl.cz/ntk/nusl-231934.
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This diploma thesis deals with finding and verification of appropriate technological parameters of SLM technology for the processing of aluminum alloy 2618. In the theoretical part, an introduction to additive manufacturing of aluminum alloys and general description of processes occurring during SLM production is given. Based on general knowledge were designed different types of testing samples produced by sintering the metallurgical powder using 400 W ytterbium fiber laser, which so far in the literature for aluminum alloy 2618 were not described. As the result, the technological parameters dependence on relative density and the detailed overview of the 2618 alloy processing by SLM technology is determined.
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Kočica, Martin. "Zpracování slitin mědi pomocí technologie selective laser melting." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2016. http://www.nusl.cz/ntk/nusl-241911.
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This diploma thesis deals with finding copper alloy suitable for processing SLM technology and determining the process parameters leading to a relative density close to the full material. The theoretical part provides an insight into additive technology and the processing of new alloys in SLM. Work also contains a search report of processed copper alloys used in SLM. Based on the theoretical part were designed test samples and method of evaluation. Samples were produced by melting metallurgical powder using ytterbium laser with an output power 400 W. The testing is divided into three stages; Determination of the parameters of the SLM process, Debug strategies for larger parts, Geometric precision and mechanical testing. Based on the results was determined dependence of relative density on the input parameters. For the best parameters were determined geometric precision correction and mechanical properties.
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Folkes, Janet Ann. "Laser surface melting and alloying of titanium alloys." Thesis, Imperial College London, 1987. http://hdl.handle.net/10044/1/38315.
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Chen, Zhen-da. "Laser surface melting and alloying of cast irons." Thesis, Imperial College London, 1987. http://hdl.handle.net/10044/1/38260.
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Pacquentin, Wilfried. "Contribution à l'étude des propriétés physico-chimiques des surfaces modifiées par traitement laser : application à l'amélioration de la résistance à la corrosion localisée des aciers inoxydables." Phd thesis, Université de Bourgogne, 2011. http://tel.archives-ouvertes.fr/tel-00676332.
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Les matériaux métalliques sont utilisés dans des conditions de plus en plus sévères et doivent présenter une parfaite intégrité sur des périodes de plus en plus longues. L'objectif de ce travail de thèse est d'évaluer le potentiel d'un traitement de refusion laser pour améliorer la résistance à la corrosion d'un acier inoxydable de type 304L ; l'utilisation du laser dans le domaine des traitements de surface constituant un procédé en pleine évolution à cause des changements récents dans la technologie des lasers. Dans le cadre de ce travail, le choix du laser s'est porté sur un laser nano-impulsionnel à fibre dopée ytterbium dont les caractéristiques permettent la fusion quasi-instantanée sur quelques microns de la surface traitée, immédiatement suivie d'une solidification ultra-rapide avec des vitesses de refroidissement pouvant atteindre 1011 K/s. La combinaison de ces processus favorise l'élimination des défauts surfaciques, la formation de phases hors équilibre, la ségrégation d'éléments chimiques et la formation d'une nouvelle couche d'oxyde dont les propriétés sont gouvernées par les paramètres laser. Afin de les corréler avec la réactivité électrochimique de la surface, l'influence de deux paramètres laser sur les propriétés physico-chimiques de la surface a été étudiée : la puissance du laser et le taux de recouvrement des impacts laser. Pour clarifier ces relations, la résistance à la corrosion par piqûration des surfaces traitées a été déterminée par des tests électrochimiques. Pour des paramètres laser spécifiques, le potentiel de piqûration d'un acier inoxydable de type 304L augmente de plus de 500 mV traduisant ainsi une meilleure tenue à la corrosion localisée en milieu chloruré. L'interdépendance des différents phénomènes résultant du traitement laser a rendu complexe la hiérarchisation de leur effet sur la sensibilité de l'alliage testé. Cependant, il a été montré que la nature de l'oxyde thermique formé au cours de la refusion laser et ses défauts sont du premier ordre pour l'amorçage des piqûres.
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Thomas, Daniel. "The development of design rules for selective laser melting." Thesis, Cardiff Metropolitan University, 2010. http://hdl.handle.net/10369/913.
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The research reported in this thesis focuses on assisting the design process in respect of end use metallic products produced using the Selective Laser Melting (SLM) technology. The advancements in layer additive manufacturing technologies such as SLM have enabled the manufacture of end use products directly from Computer Aided Design data. Many companies and researchers are exploring the application of SLM in industry for specific applications, such as the mass customisation of biomedical implants and novel lattice structures. However, bridging SLM from research into mainstream manufacturing is not straightforward, as demanding industry standards and compliance need to be fulfilled. Additive Manufacturing (AM) technologies are often perceived by designers as being able to generate all conceivable geometries. However, SLM is not completely freeform as the inherent process difficulties can distort many part geometries, and designers often lack an understanding of these process issues and their effect on the final SLM product. The aim of this research is to address this lack of design knowledge, by developing a set of design rules to allow for more predictable and reliable results when manufacturing parts with SLM. This thesis documents how the design rules were created. Firstly, the geometric limitations of SLM were evaluated through a quantitative cyclic experimental methodology. Part orientation, fundamental geometries and compound design features were explored until self-supporting parts with the optimum part accuracy were achieved. Design rules were then created and evaluated through a series of interviews with industrial and academic design professionals.
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Brooks, Wesley Keith. "The creation of lattice structures using selective laser melting." Thesis, University of Liverpool, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.569197.
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This research focuses on reducing the limitations imposed on the repeating topologies in lattice structures that restrict what can be created using the RealiZer Selective Laser Melting (SLM) machine. The creation of regular, randomly perturbed, polar mapped, and random metallic lattice structures using SLM apparatus is reported and discussed in this thesis. It was observed that a new technique was required to generate the slice data files used to control the SLM equipment in order to create structures that measured significantly more than 10 cells in each axis. The research details the motivations behind the development of the computational methods utilised to develop lattice parts and how the iterations of these methods enabled different areas of research to progress. The limits of the angles from the horizontal that elements could be built are reviewed and scanning techniques are developed that create elements below these values. In order to create horizontal links significant proportions of the machine control software were replaced with software developed during the course of the research. This is discussed at length along with how the limitations on the number of processing parameters available could be removed and how pauses which let sections of the melt on horizontal links freeze before processing the next section could be used. It is suggested that systems or experimental set ups are developed that allow greater control over the duration of these pauses. This would enable further research into the processing of horizontal links, developing them to the point where they are mechanically consistent and comparable to other links in the structures
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Han, Quanquan. "Selective laser melting of an advanced Al-Al2O3 nanocomposite." Thesis, Cardiff University, 2017. http://orca.cf.ac.uk/104826/.
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Selective laser melting (SLM) has been widely used to manufacture customised metallic parts because it provides an integrated way to manufacture three-dimensional (3D) parts from computer-aided design models after several sub-processes. On the other hand, aluminium-based nanocomposites are widely used in the aerospace and automotive industries due to their light weight, high specific strength, excellent wear resistance, but their manufacturability and mechanical properties are not well understood when these new materials are employed in SLM. This is an important consideration because, compared with traditional manufacturing technologies, SLM offers the ability to manufacture engineering parts with very complex geometries by employing a layer-by-layer manufacturing principle. Hence, this thesis systematically studies the SLM of an advanced Al-Al2O3 nanocomposite that is synthesised using high-energy ball-milling (HEBM) process. The aim of this study is to use SLM to fabricate a nearly full dense Al-Al2O3 nanocomposite composed of 96 vol.% Al and 4 vol.% Al2O3 powder. The synthesis and characterisation of ball-milled powder is the first contribution of this study, which also investigates the influence of milling and pause duration on the fabrication of ball-milled composite powder. The second contribution of this work is the development of a 3D finite element model to predict the thermal behaviour of the first layer’s composite powder. Both the transient temperature distribution and molten pool dimensions are predicted within the laser scanning, which VI enables a more efficient selection of the process parameters (e.g. hatch spacing and scanning speed). The third contribution of this study is the optimisation of the SLM process parameters and microstructure investigation of the fabricated samples. The optimum laser energy density and scanning speed that are used to fabricate nearly full dense Al-Al2O3 nanocomposites are found to be 317.5 J/mm3 and 300 mm/s, respectively. The relative density is evaluated by quantifying the porosity on both the horizontal and vertical sections. The fabricated composite parts were observed to exhibit a very fine granular-dendrite microstructure due to the rapid cooling, while the thermal gradient at the molten pool region along the building direction was found to facilitate the formation of columnar grains. The final contribution of this study is the investigation of mechanical properties such as tensile strength, microhardness and macro and nanoscale wear behaviour. Compared to pure Al, the addition of 4 vol.% Al2O3 nanoparticulates was found to contribute to a 36.3% and 17.5% increase in the yield strength and microhardness of the composite samples, respectively. Cold working was found to contribute to a 39% increase in microhardness due to grain deformation. The pin-on-disc wear testing and atomic force microscopy (AFM) nanoscratching were performed to study the macro and nanoscale wear behaviour of the fabricated samples, respectively.
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Mumtaz, Kamran A. "Selective laser melting of Inconel 625 using pulse shaping." Thesis, Loughborough University, 2008. https://dspace.lboro.ac.uk/2134/33630.
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Selective Laser Melting (SLM) is an additive manufacturing technology that consolidates layers of metal powder using a high power laser. The laser's small spot size and relative accuracy facilitates the production of high resolution parts with great complexity that would be otherwise difficult to manufacture using conventional manufacturing techniques (e.g. casting, machining etc.). The possibility to build thin wall high resolution parts complements the technology's main advantage and extends its manufacturing capabilities. The high heat input delivered by the laser and complex melt pool dynamics, requires that laser process parameters are carefully controlled in order to prevent solidified parts from exhibiting poor properties such as a high surface roughness and poor resolution.
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Zheng, Xiao-Qin Materials Science & Engineering Faculty of Science UNSW. "Packing of particles during softening and melting process." Awarded by:University of New South Wales. School of Materials Science & Engineering, 2007. http://handle.unsw.edu.au/1959.4/31517.
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Softening deformation of iron ore in the form of sinter, pellet, and lump ore in the cohesive zone of an ironmaking blast furnace is an important phenomenon that has a significant effect on gas permeability and consequently blast furnace production efficiency. The macroscopic softening deformation behavior of the bed and the microscopic deformation behavior of the individual particles in the packed bed are investigated in this study using wax balls to simulate the fused layer behavior of the cohesive zone. The effects of softening temperature, load pressure, and bed composition (mono - single melting particles, including pure or blend particles vs binary ??? two different melting point particles) on softening deformation are examined. The principal findings of this study are: 1. At low softening temperatures, an increase in load pressure increases the deformation rate almost linearly. 2. At higher softening temperatures, an increase in load pressure dramatically increases the deformation rate, and after a certain time there is no more significant change in deformation rate. 3. The bed deformation rate of a mono bed is much greater than that of a binary one. 4. In a binary system, the softening deformation rate increases almost proportionally with the increase in the amount of lower melting point wax balls. 5. In a mono system with blend particles, the content of the lower melting point material has a more significant effect on overall bed deformation than the higher melting point one. 6. The macro softening deformation of the bed behaves the theory of creep deformation. 7. A mathematical model for predicting bed porosity change due to softening deformation based on creep deformation theory has been developed. 8. Increase in load pressure also reduces the peak contact face number of the distribution curves, and this is more prominent with higher porosity values. 9. The contribution of contact face number to bed porosity reduction is more pronounced in a mono system than in a binary system. 10. The porosity reduction in a binary bed is more due to the contact face area increase, presumably of the lower melting point particles. 11. The mono system has a single peak contact face number distribution pattern while the binary system exhibits a bimodal distribution pattern once the higher melting point material starts to deform. 12. In a binary system, an increase in deformation condition severity tends to reduce the contact face number of the higher melting point material without having to increase the contact face number of the lower melting point material accordingly to achieve a given porosity.
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Jerrard, Peter George Eveleigh. "Selective laser melting of advanced metal alloys for aerospace applications." Thesis, University of Exeter, 2011. http://hdl.handle.net/10036/3576.
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Research focused on the selective laser melting (SLM) of stainless steels and aluminium alloys. For steels, the possibility of creating a magnetically graded material was demonstrated as well as the ability to improve consolidation with austenitic and martensitic stainless steel powder mixtures. Stainless Steel/CoCr hybrid samples were also manufactured and tested to investigate the advantages of functionally graded materials (FGMs). Al alloy research began with examining the requirements for successful Al alloy consolidation in SLM and through experimentation it was found that Al alloys with good welding properties were the best choice: pure Al was found to be completely unsuitable. 6061 Al alloy was then used as a base material to manufacture Al-Cu alloy samples. Single layer SLM samples were produced first, which resulted in recognised Al-Cu microstructures forming. Multilayer Al alloy SLM research resulted in the discovery of the theorised ability to manufacture Al-Cu alloy parts with a nanocrystalline Al matrix with dispersed Al2Cu quasicrystals, resulting in a material comparable to a metal matrix composite that showed excellent corrosion resistance and compressive strength. Finally, a demonstration part was made to test the capability of the SLM process producing an aerospace type geometry using a customised Al alloy. Observations during manufacture and post process analysis showed that Al alloys were susceptible to changes in mechanical properties due to the geometry of the manufactured part.
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Zhang, Dongyun [Verfasser]. "Entwicklung des Selective Laser Melting (SLM) für Aluminiumwerkstoffe / Dongyun Zhang." Aachen : Shaker, 2004. http://d-nb.info/1181603994/34.
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