No description available.

No description available.

Laser powder bed fusion (L-PBF) refers to an additive manufacturing (AM) process in which a high-intensity laser source melts powders in a layer-by-layer manner to fabricate parts based on a computer-aided design (CAD) model without almost any geometrical limitations. The development of the L-PBF process has provided an outstanding opportunity to manufacture unique parts which are practically impossible to be produced by conventional manufacturing methods. The L-PBF process also does not require intricate build tools and assembly processes. However, quality issues such as non-uniform microstructure or mechanical properties, porosities, and surface roughness deteriorate the quality of the parts fabricated by the L-PBF process. Therefore, the reliability and the repeatability of the process are required to be addressed. This study deals with improving the quality of the part fabricated by the L-PBF process and making the process more reliable and repeatable. The control approach was employed to elevate the quality of the final part from three different aspects. First, making the microstructure and microhardness of the part uniform through a control approach was investigated. Three controllers, namely, proportional (P), adaptive P, and quasi sliding mode, were developed to control the melt pool temperature for the Inconel 625 superalloy. An analytical-experimental model was presented to evaluate the performance of controllers via simulation. A monitoring system consisting of a two-color pyrometer was utilized off-axially to monitor the melt pool temperature for use by the controllers as a feedback signal. The results indicated that the control approach led to microhardness and microstructure uniformity, resulting from the reduced variation in the primary dendrite arm spacing compared to the case with constant process parameters. Second, the control approach was utilized to produce optimum parts instead of using the energy density criterion. Temperature domains corresponding to the most common porosities, namely, lack of fusion (LOF), lack of penetration (LOP), and keyhole, were determined in a range of process parameters using a thermal imaging system. A safe zone was introduced by defining a lower and an upper limit based on the critical temperatures causing transitions from LOP to defect-free and from defect-free to keyhole zones, respectively. A proportional-integral-derivative (PID) controller was used to maintain the melt pool temperature within the safe zone during the L-PBF process for Inconel 625 and avoid the formation of porosities, regardless of the initial condition selected and the scanning speed employed. In all cases, a short settling time in the order of the printing time for a few layers was required to reach the steady-state condition at which defect-free parts could be obtained. Finally, minimizing the top surface roughness of the parts manufactured by the L-PBF process by deploying a Feedforward plus Feedback control system was targeted in this study. The most common factors affecting the surface quality, namely, balling, lack of inter-track overlap, overlapping curvature of laser scan tracks, and spatters, were investigated through a monitoring system consisting of a high-speed camera, a zooming lens, and a short pass filter. The desired melt pool width and the critical value for the level of spatters were determined using the imaging system and subsequent image processing. An experimental model was developed, and the control system was designed accordingly. Both simulations and experimental results showed excellent transient performance of the control system to reach the desired melt pool width only after printing a few layers. Also, the control system was evaluated at different scanning speeds and with different geometries. The results obtained from this study indicated that controlling the geometry of the melt pool can mitigate significant defects occurring during the process and minimize the top surface roughness. / Thesis / Doctor of Philosophy (PhD)

La Fabrication Additive (FA) vient aujourd’hui bouleverser des habitudes de conception bien ancrées, et suscite dans le même temps un intérêt grandissant pour les perspectives qu’elle offre pour l’innovation produit. Pourtant, alors que les enjeux liés à l’innovation sont prépondérants en conception amont, peu de concepteurs connaissent et utilisent le potentiel des connaissances FA pour développer puis sélectionner des solutions créatives. Dans ce contexte, notre recherche a pour objectif d’augmenter la capacité d’innovation des concepteurs en intégrant des connaissances FA lors de la conception amont. Pour cela nous proposons d’intégrer des connaissances FA explicites dites « au juste besoin », c’est-à-dire dont le contenu, l'instanciation et le support sont adaptés aux besoins des équipes de conception. De plus, nous proposons que cette intégration s’effectue dans un modèle de conception permettant l’approche Design With Additive Manufacturing (DWAM). Nos apports sont la proposition : d’une démarche, basée sur le Knowledge Management, permettant de repérer, capitaliser puis valoriser les connaissances FA au juste besoin ; mais également d’un modèle de conception amont en 3 étapes dans lequel les connaissances FA utiles à l’approche DWAM sont spécifiées. Enfin, ce modèle enrichi est valorisé dans un outil numérique support afin de faciliter le travail collaboratif et concourant. / The onset of Additive Manufacturing (AM) upsets design practices and is receiving attention because its potential is promising for product innovation. However, while innovation issues are paramount during early design stages, few designers have sufficient knowledge about AM and use it poorly to develop creative solutions. Thus, our research objective is the increase of the innovation capacity of the design team through the integration of AM knowledge into early design. To do this, we propose to use “just needed” AM knowledge, i.e., AM knowledge whose contents, supports and instancing are tailored to the design team needs. Moreover, we propose that this integration takes place in a design model that allows the Design With Additive Manufacturing (DWAM) approach. Our contributions are both the proposal of a methodology based on Knowledge Management dedicated to the identification, the capitalization and the valorization of the “just needed” AM knowledge; and of a design model in 3 stages, in which the useful for DWAM approach AM knowledge is specified. Finally, this enriched model is valued in a digital tool in order to improve collaborative and concurrent design.

Two direct consolidation methods usually used for advanced ceramics have been combined in this project in order to develop a novel fabrication route for traditional ceramics. Specifically the method used is based on the Additive Manufacturing extrusion process using direct writing of high solid loading ceramic pastes and then freeze-casting to solidify the deposited material. This novel fabrication method, for which a patent has been granted, has been christened “Direct Writing Freeze-Casting” (DWFC). Although the DWFC process is the subject of investigation by other researchers for a range of different applications, including the production of medical implants with alumina, the research presented in this thesis focuses on its use in the manufacture of white wares, giftware, and applied arts and crafts in general. This new system will provide designers, potters, artists, craft makers and manufacturers with a flexible and automated way of manufacturing porcelain objects. One of the major challenges to be overcome to exploit the DWFC process is the development of suitable slurry material formulations. Initial trials demonstrated that it is not possible to use conventional clay based porcelain materials with a platelet shaped microstructure which inhibits freeze casting. In this thesis the development and characterisation of non plastic porcelain slurry, based on substitution of kaolin (clay) with a calcined clay material (molochite), which can be processed using this new method is presented. The new non plastic porcelain formulation, which has a high solid load of 75.47% wt., has been subjected to detailed analysis to assess its suitability at each stage of the process; extrusion, freeze-casting (solidification) and firing.

Recent development of additive manufacturing technologies has led to lack of information on the base materials being used. A need arises to know the mechanical behaviors of these base materials so that it can be linked with macroscopic mechanical behaviors of 3D network structures manufactured from the 3D printer. The main objectives of my research are to characterize properties of a material for an additive manufacturing method (commonly referred to as 3D printing). Also, to model viscoelastic properties of Procast material that is obtained from 3D printer. For this purpose, a 3D CAD model is made using ProE and 3D printed using Projet HD3500. Series of uniaxial tensile tests, creep tests, and dynamic mechanical analysis are carried out to obtained viscoelastic behavior of Procast. Test data is fitted using various linear and nonlinear viscoelastic models. Validation of model is also carried out using tensile test data and frequency sweep data. Various other mechanical characterization have also been carried out in order to find density, melting temperature, glass transition temperature, and strain rate dependent elastic modulus of Procast material. It can be concluded that melting temperature of Procast material is around 337°C, the elastic modulus is around 0.7-0.8 GPa, and yield stress is around 16-19 MPa.

The main purpose of this thesis is to see if it is possible to use additive manufacturing(AM) for field repair and maintenance of the assault rifle AK5C, by finding a suitableadditive manufacturing process and make a functional evaluation of the additivemanufactured components: hammer axis, gas cylinder and the magazine follower. TheSwedish Defense Materiel Administration (FMV) is an administration that supplies theSwedish armed forces with materiel. Therefore, it is in their interest to investigate if itis possible to use AM for field repair and maintenance in example Mali or Afghanistan.Based on a survey, and the fact that the components are purelystructural Powder Bed Fusion AM was selected. The hammer axis was made in amargining steel MS1, the gas cylinder in the nickel-alloy called Inconel 718 and themagazine follower was made in a polymer called nylon 12.The functional evaluation of the components took place at Saab in Östersund, whereeach component was placed in the rifle. The rifle was fired 1000 rounds with thehammer axis, 1000 rounds with the gas cylinder and 500 rounds with the magazinefollower. The functional test for the components was successful, there were also nomajor changes in dimensions and weight except for the hammer axis. The diameterfor the hammer axis went from 5,00 mm before the functional test to 4,98 mm afterthe functional test. The microscope images showed thatabrasion had occurred, not only for the hammer axis but also for the magazinefollower, due to friction. Firing speed was also measured and it should be over 600rounds/min, if everything works properly. The hammer axis had a firing speed of 639rounds/min which is good while the gas cylinder only had a firing speed of 595rounds/min. This was because the inner diameter of the cylinder was too big, causinggas leaking and pressure drop inside the gas cylinder.In conclusion, additive manufacturing does allow for fabrication of functional spareparts – at least these evaluated here.

Process-structure-property relationships in material extrusion additive manufacturing (MEAM) are complex, non-linear, and poorly understood. Without proper characterization of the effects of each processing parameter, products produced through fused filament fabrication (FFF) and other MEAM processes may not successfully reach the material properties required of the usage environment. The two aims of this thesis were to first use an informatics approach to design a workflow that would ensure the collection of high pedigree data from each stage of the printing process; second, to apply the workflow, in conjunction with a design of experiments (DOE), to investigate FFF processing parameters. Environmental, material, and print conditions that may impact performance were monitored to ensure that relevant data was collected in a consistent manner. Acrylonitrile butadiene styrene (ABS) filament was used to print ASTM D638 Type V tensile bars. MakerBot Replicator 2X, Ultimaker 3, and Zortrax M200 were used to fabricate the tensile bars. Data was analyzed using multivariate statistical techniques, including principal component analysis (PCA). The magnitude of effect of layer thickness, extrusion temperature, print speed, and print bed temperature on the tensile properties of the final print were determined. Other characterization techniques used in this thesis included: differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and scanning electron microscopy (SEM). The results demonstrated that printer selection is incredibly important and changes the effects of print parameters; moreover, further investigation is needed to determine the sources of these differences.

No description available.

Lithophane is a translucent image created by varying the plate thickness; the image is observed using a back lit light source. Software Bmp2CnC linearly converts the black and white image grayscale into the thickness, thus generates CAD file and lithophane is fabricated by additive manufacturing machines. Additive manufacturing makes highly complex lithophane fabrication possible. It is a convenient, rapid, green, design-driven, and high precision way to make lithophanes, and no post processing is needed. Optical properties of laser sintered polyamide 12 translucent additive manufactured parts were analyzed in this dissertation. First, selected optical properties of laser sintered polyamide 12 blank plates under different monochromatic light and white light were investigated and applied in production of laser sintered lithophanes to achieve better performance. A spectrophotometer was used to measure the transmittance of visible light through laser sintered polyamide 12 plates as a function of plate thickness. The transmittance decreased with increasing plate thickness according to a modified Beer-Lambert Law, and it varied significantly depending on the monochromatic wavelength. Monochromatic LEDs were used to assess the wavelength dependence on the transmission and contrast. Highest transmission was observed with green light (540 nm), and poorest transmission was measured for yellow light (560 nm). Second, several parameters affecting lithophane manufacturing performance were analyzed including lithophane orientation with respect to light source, brightness and contrast versus plate thickness and grayscale level, quantized plate thickness correction, surface finish quality, and manufacturing orientation. It was found that brightness was relative to the plate thickness. The contrast was defined by the lithophane grayscale level, which was influenced by sintering layer thickness, plate thickness, and sintering orientation. Thinner sintering layers resulted in more grayscale levels of the image and smaller difference between the theoretical thickness and actual thickness. Relatively larger plate thickness defined greater contrast; however, the plate thickness was limited due to the light transmission. Lithophane quality was largely improved by changing the manufacturing orientation from the XY plane orientation to the ZX/ZY plane orientation. The grayscale level changed continuously when parts were constructed in the z orientation. Third, other thermoplastic semi-crystalline materials were analyzed for LS optically translucent part production. Last, plates and lithophanes were built using a different AM platform: stereolithography (SL) with Somos® ProtoGen[Trademark] O- XT 18420 white resin. Different optical properties and lithophane performance were found and compared with PA 12 parts. In conclusion, laser sintered polyamide 12 optical properties varied with light wavelength and reached the maximum under green light. When building in the XY plane, thinner layer thickness (0.07 mm) and relative thicker maximum plate thickness (3.81 mm) leaded to higher contrast and greyscale level. Lithophane quality was largely improved when fabricated in the ZX/ZY plane orientation. Lithophanes made from stereolithography were analyzed but showed lower contrast due to the optical property difference of the white resin. Laser sintered lithophanes serve as an interesting and complex LS industrial application. Optical properties, manufacturing aspects, and other related issues were analyzed and discussed in this dissertation. Future work may include the use of nanocomposites for optimal lithophane performance, and more precise manufacturing processing to improve the lithophane resolution. / text