• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 64
  • 35
  • 11
  • 7
  • 3
  • 3
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 156
  • 156
  • 156
  • 77
  • 75
  • 48
  • 42
  • 38
  • 31
  • 30
  • 28
  • 26
  • 24
  • 22
  • 22
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Modélisations multiphysiques à deux échelles du procédé de fabrication additive par fusion laser de lit de poudre / Multiphysics modeling at two scales of the selective laser melting additive manufacturing process

Durand, Pierre-Yves 25 April 2017 (has links)
Quel que soit le secteur d’activité, les procédés de fabrication additive pour les matériaux métalliques ont un fort potentiel industriel, spécifiquement pour la production de pièces à haute valeur ajoutée. Le secteur de l’outillage est l’un des utilisateurs de ces procédés, et plus particulièrement du Selective Laser Melting (SLM). Ce procédé permet de diminuer les coûts et les temps de production des outillages, tout en augmentant la complexité des pièces fabriquées. Cependant, pour améliorer la qualité des pièces fabriquées, une meilleure compréhension des mécanismes physiques qui le régissent est nécessaire. Dans ce travail de thèse, consacré à la modélisation du procédé SLM, les approches suivies sont multiphysiques à deux échelles. La première échelle de modélisation, utilisant la méthode Volume Of Fluid, correspond à la fusion d’un lit de poudre par un laser puis sa solidification. Le lit de poudre numérique est produit à partir d’un générateur spécifique basé sur la granulométrie identifiée expérimentalement. Après certaines hypothèses simplificatrices posées sur les phénomènes physiques à modéliser, la tension superficielle a été implémentée et a nécessité l’utilisation de la méthode des « heights functions ». La seconde échelle de modélisation correspond à la construction d’une succession de cordons à l’aide de la méthode des éléments finis. Le modèle thermomécanique utilise la méthode « element birth » pour se rapprocher au plus près des conditions réelles du procédé. Après leur validation par des essais expérimentaux, les simulations ont permis de prédire le champ de température, la largeur de la zone fondue, ainsi que la formation du « keyhole ». / Regardless the industry, additive manufacturing processes for metallic materials have a great industrial potential, especially to product high added value parts. One of the main users of these processes, and more specifically the Selective Laser Melting (SLM), is the tooling industry for plastics processing. It make possible to reduce production costs and manufacturing times while increasing the complexity of manufactured parts. However, in order to improve the quality of the latter and ensure their certifications, a better insight into the related physical phenomena undergone by the material during the process is still needed. In this PhD thesis, the SLM process modeling is multiphysic and concerns two different scales. The first modeling scale uses the Volume Of Fluid method to model the powder bed melting and its ensuing solidification. The numerical powder bed is computed thanks to a specific generator enabling to take account for the experimental granulometry. Once some simplifying assumptions on the physical phenomena stated, the surface tension has been implemented requiring the "heights functions" method use. The second modeling scale corresponds to the building of laser tracks series through the finite element method. The thermomechanical approach uses the element birth method in order to meet as far as possible the experimental conditions. Following its assessment through experiment/simulation face off, model have enable to predict the temperature field and the melted zone width as well as the keyhole formation.

Zpracování vysokopevnostní hliníkové slitiny AlSi9Cu3 technologií selective laser melting / Processing of high-strength aluminum alloy AlSi9Cu3 using selective laser melting technology

Suchý, Jan January 2017 (has links)
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.

Selective laser melting of advanced metal alloys for aerospace applications

Jerrard, Peter George Eveleigh January 2011 (has links)
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.

Generative Serienfertigung von individuellen Produkten aus CoCr mit dem Selektiven Laser-Schmelzen /

Uckelmann, Ingo. January 2007 (has links)
Techn. Hochsch., Diss.--Aachen, 2006.

Defect Detection in Selective Laser Melting

Foster, Moira 01 June 2018 (has links) (PDF)
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.

The Effect of Laser Power and Scan Speed on Melt Pool Characteristics of Pure Titanium and Ti-6Al-4V alloy for Selective Laser Melting

Kusuma, Chandrakanth 01 June 2016 (has links)
No description available.

Preliminary Investigations Into Selective Laser Melting

Otsu, David Takeo 01 June 2017 (has links) (PDF)
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.

Optimalizace SLM procesu pro výrobu úsťového zařízení útočné pušky / Optimization of SLM process for manufacturing of assault rifle muzzle device

Kubrický, Jakub January 2017 (has links)
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.

Návrh výplňových prvků s trabekulární strukturou pro revizní implantát kolenního kloubu / Design of filling elements with trabecular structure for revision implant of total knee arthroplasty

Lang, Roman January 2014 (has links)
This diploma thesis describes the design of filling element with trabecular structure for revision implant of total knee arthroplasty. Design of the filling element is created by the digital data of the patient tissue. Production of a functional sample is performed using additive technology Selective Laser Melting. This work also include analyze of the accuracy of this technology for the production of titanium alloy Ti6Al4V.

Stainless steels fabricated by laser melting : Scaled-down structural hierarchies and microstructural heterogeneities

Saeidi, Kamran January 2016 (has links)
Additive manufacturing is revolutionizing the way of production and use of materials. The clear tendency for shifting from mass production to individual production of net-shape components has encouraged using selective laser melting (SLM) or electron beam melting (EBM). In this thesis, austenitic, duplex and martensitic stainless steel parts were fabricated by laser melting technique using fixed laser scanning parameters. The fabricated steel parts were characterised using XRD, SEM, TEM/STEM, SADP and EBSD techniques. Mechanical properties of the fabricated steel parts were also measured. The mechanism of the evolution of microstructure during laser melting as well as the mechanism of the effect of developed microstructure on the mechanical properties was investigated. It was found that the intense localized heating, non-uniform and asymmetric temperature gradients and subsequently fast cooling introduces unique high level structural hierarchies and microstructure heterogeneities in laser melted steel parts. A unique structural hierarchy from the millimetre scale melt pools down to the sub-micron/nano scale cellular sub-grains was observed. The cellular sub-grains were 0.5-1μm with Molybdenum enriched at the sub-grain boundaries in SLM 316L. The Mo enriched cell boundaries affected the chemical and microstructure stability of the post heat treated samples. Well dispersed and large concentration of dislocations around the cell boundaries and well distributed oxide nano inclusions, imposed large strengthening and hardening effect that led to relatively superior tensile strength (700 MPa), yield strength (456 MPa), and microhardness (325Hv) compared to those of HIP 316L steel. The in-situ formation of oxide nano inclusions provided a unique way for preparation of oxide dispersion-strengthened (ODS) steel in a single process. The formation of oxide nano inclusions in the very low oxygen partial pressure of laser chamber was thermodynamically explained. High concentration of nano size dislocation loops, formation of nitride phases along with nitrogen enriched islands and oxide nano inclusions lead to strong dislocation pinning effect which strengthened the laser melted duplex stainless steel with a total tensile strength of 1321 MPa, yield strength of 1214 MPa and microhardness of 450HV. The grade 420 stainless steel was laser melted in Ar and N2 atmosphere which also showed a two level hierarchy with nanometric martensite lathes embedded in parental austenite cellular grains. The Ar treated sample had relatively higher retained austenite, lower YS (680-790 MPa) and UTS (1120-1200 MPa) compared to those treated in N2 (YS= 770-1100 MPa, UTS=1520-1560 MPa). The mechanism of the effect of atmosphere on phase transformation was explained. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Submitted.</p>

Page generated in 0.0889 seconds