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To enhance mechanical and/or electrical properties of composite materials used in additive manufacturing, nanoparticles are often time deposited to form nanocomposite layers. To customize the mechanical and/or electrical properties, the thickness of such nanocomposite layers must be precisely controlled. A thickness model of filter cakes created through a spray assisted vacuum filtration is presented in this paper, to enable the development of advanced thickness controllers. The mass transfer dynamics in the spray atomization and vacuum filtration are studied for the mass of solid particles and mass of water in differential areas, and then the thickness of a filter cake is derived. A two-loop nonlinear constrained optimization approach is used to identify the unknown parameters in the model. Experiments involving depositing carbon nanofibers in a sheet of paper are used to measure the ability of the model to mimic the filtration process.

The world of additive manufacturing revolves around speed and repeatability. Inherently, the process of 3D printing is plagued with variability that fluctuates with every material and parameter modification. Without proper qualification standards, processes can never become stable enough to produce parts that may be used in aerospace, medical, and construction industries. These industries rely on high quality metrics in order to protect the lives of those who may benefit from them. To establish trust in a process, all points of variation must be controlled and accounted for every part produced. In instances where even the best process controls are enacted, there still may be situational unknowns that can cause detrimental defects, often on micron scales. Through in-situ monitoring techniques, such as visual or acoustic monitoring, a secondary level of quality assessment can be performed. This type of real time monitoring solution can be used in a variety of ways to help reduce scrap rate, increase overall quality, and improve the mechanical characteristics of a newly developing material. In this proposal, a goal was set to develop a system that can be a low-cost alternative to a comparable acoustic monitoring system. This design is meant to be a low fidelity concept that can alert a user of any potential anomalies within a build by detecting spikes in acoustic emissions. The overall success of this experiment is set on two conditions. First, the new low-cost system should be mountable on various types of machines. Second, this system should demonstrate some level of equivalency to a similar system. These two situations were successfully met as the system was able to provide indications of anomalies present within a build. The system was calibrated and tuned to be able to measure signals on a SLM 125 running 316L powder. Minor modifications to the code and system can make it adaptable to different types of equipment such as CNC’s, bandsaws, casting processes, and other advanced manufacturing equipment. The model can be attenuated to support higher or lower frequencies as well as different types of acoustic sensors, which demonstrates the vast potential that this system can provide for detecting different types of defects.

In this project, the scan strategy of selective laser melting (SLM) for thin walled structures was investigated by changing laser parameters and tool path. Producing thin walled structures is difficult due to defects such as warpage and porosity. A layer on the SLM 125 consists of hatch volume, fill contours, and borders, however, for thin walls, hatch volume can become unavailable, resulting in a solely border/fill contour laser tool path. Three central composite designs (CCD) were created to optimize the laser parameters of borders to minimize leakage rate and porosity. The two factors changed were border laser power and scanning speed. The center points of the CCDs were 0.24 J/mm, 0.20 J/mm, and 0.16 J/mm, respectively. This border linear energy density value was calculated by (border laser power / border scanning speed). A machined aluminum fixture was designed and assembled with pneumatics to perform a pressure drop leakage test. Additionally, micrographs of 500μm and 200μm wall thicknesses were analyzed to study between and within layers as well as melt pool dimensions. In the 200μm thick samples, there was delamination and insufficient overlap in border only prints. For border only prints, a lower border linear energy density is recommended, similar to Cal Poly’s hatch volume optimized parameters of 0.15 J/mm.

Laser powder bed fusion (LPBF) remains a predominately open-loop additive manufacturing process with minimal in-situ quality and process control. Some machines feature optical monitoring systems but lack automated analytical capabilities for real-time defect detection. Recent advances in machine learning (ML) and convolutional neural networks (CNN) present compelling solutions to analyze images in real-time and to develop in-situ monitoring. Approximately 30,000 selective laser melting (SLM) build images from 31 previous builds are gathered and labeled as either “okay” or “defect”. Then, 14 open-sourced CNN were trained using transfer learning to classify the SLM build images. These models were evaluated by F1 score and down selected to the top 3 models. The top 3 models were then retrained and evaluated using Dietterich’s 5x2 cross-validation and compared with pairwise student t-tests. The pairwise t-test results show no statistically significant difference in performance between VGG- 19, Xception, and InceptionResNet. All models are strong candidates for future development and refinement. Additional work addresses the entire model development process and establishes a foundation for future work. Collaborations with computer science students has produced an image pre-processing program to enhance as-taken SLM images. Other outcomes include initial work to overlay CAD layer images and preliminary hardware integration plan for the SLM machine. The results from this work have demonstrated the potential of an optical layer-wise image defect detection system when paired with a CNN.

The master thesis at Sandvik Additive Manufacturing Division, Sandviken, aims at three things. The first step is to estimate the cost of a Binder jet Additive Manufacturing method and identify the key cost drivers in the manufacturing process, since cost estimation can help the organisation to understand the cost factors that are affecting the product's price. Also assisting the sales team to create a foundation to price quote their customers and raise profit margins. Hence the first part of the thesis emphasizes creating an easy-to-use template for the organization's production and sales teams. The second part of the thesis is to provide an Excel sheet that is simple to use for computing the yearly budgets so that it serves as a technique for forecasting impending outflows within the company. Hence, a quarterly and yearly budgeting template that the sales and production team can use at Sandvik AM division is designed. The final objective of this thesis is to establish the Binder Jet machine's Overall Equipment Efficiency key performance indicator. This is done by taking into account availability, performance, and quality. These three factors are tracked from the additive manufacturing machines using an automated OEE Key Performance Indicator calculator that collects data from the build reports into Excel using the power query tool. / Examensarbetet vid Sandvik Additive Manufacturing Division, Sandviken, syftar till tre saker. Det första steget är att uppskatta kostnaden för en Binder jet Additive Manufacturing-metod och identifiera de viktigaste kostnadsdrivkrafterna i tillverkningsprocessen, eftersom kostnadsuppskattning kan hjälpa organisationen att förstå de kostnadsfaktorer som påverkar produktens pris. Hjälper även säljteamet att skapa en grund för att prissätta sina kunder och höja vinstmarginalerna. Därför fokuserar den första delen av avhandlingen på att skapa en lättanvänd mall för organisationens produktions- och säljteam. Den andra delen av uppsatsen är att tillhandahålla ett Excel-ark som är enkelt att använda för att beräkna den årliga budgeten så att det fungerar som en teknik för att prognostisera förestående utflöden inom företaget. Därför utformas en mall för kvartalsvis och årlig budgetering som sälj- och produktionsteamet kan använda på Sandvik AM-divisionen. Det slutliga målet med denna avhandling är att fastställa Binder Jet-maskinens övergripande utrustningseffektivitets nyckelprestandaindikator. Detta görs genom att ta hänsyn till tillgänglighet, prestanda och kvalitet. Dessa tre faktorer spåras från de additiva tillverkningsmaskinerna med hjälp av en automatiserad OEE Key Performance Indicator-kalkylator som samlar in data från byggrapporterna till Excel med hjälp av kraftfrågeverktyget.

Reducing the size of bulky magnetic components (inductors and transformers) in power converters can be achieved by increasing switching frequency and applying innovative designs of magnetic components. Ferrite is the most suitable bulk magnetic material for working at high frequencies but it is difficult to fabricate novel designs of ferrite magnetic components because of the limitations of conventional fabrication methods. Additive manufacturing (AM) has the potential to make customize ferrite magnetic components. One big challenge in 3D printing ferrite magnetic components is the lack of compatible and functional ferrite materials as printers' feedstock. This work focuses on developing ferrite feedstock for 3D printing ferrite magnetic components and providing a guideline for formulating ferrite feedstock by studying the effects of materials and processing parameters on major properties of the ferrite feedstock. The ferrite feedstock should not only be processable by a 3D printer but also make functional ferrite material that can work in power converters. To meet the requirements, the following four aspects of the feedstock are considered in this study: 1. the feedstock should be sinterable to achieve high enough magnetic permeability; 2. magnetic permeability of the feedstock can be easily tailored; 3. rheological properties of the feedstock should ensure reasonable printing resolution; 4. the feedstock can print high aspect ratio structures without slumping. Based on the four major considerations and the desired properties, materials were selected for formulating the ferrite feedstock. The effects of materials and processing variables on the major properties of the ferrite feedstock need to be studied to develop a formulation guidance of the feedstock. The effects of materials fractions and the post-printing peak sintering temperature of the feedstock on maximizing magnetic permeability were studied. The peak sintering temperature had a significant impact on permeability and solid loading (SL) and solid loading excluding diluent (SLED) had smaller impacts. Densities and microstructures of the sintered ferrite cores were characterized to illustrate how the variables affect magnetic permeability. Adding sintering additives to the feedstock was selected as an easy and effective way to tailor the permeability of the ferrite feedstock. The effect of the fractions of two types of additives, SiO2 and Co3O4, on permeability of ferrite were studied. Both SiO2 and Co3O4 can effectively reduce the permeability of the ferrite. A novel multi-permeability toroid core design was 3D-printed with ferrite feedstocks having different fractions of SiO2 to demonstrate the feasibility of fabricating special designs of ferrite magnetics using feedstocks with additives. Core-loss densities of ferrite cores fabricated with feedstocks having different fractions of the two additives were also characterized since it is another important property of ferrite cores in high-frequency converters. Adding SiO2 significantly increases the core-loss density of ferrite cores while adding proper fractions of Co3O4 decreased core-loss density at low magnetic flux densities. The mechanisms of how Co3O4 affect permeability and core-loss density were discussed. The effect of the solid loading (SL) on print-line width resolution was studied by conducting line printing tests. The experiment results showed the best print-line width resolution was achieved using the feedstock with an intermediate SL. The is, which considered both viscosity of the feedstock and coagulation in the feedstock suspension, were discussed. The effect of solid loading excluding diluent (SLED) and UV illumination time on the achievable aspect ratio of printed feedstock was studied. Yield shear strength (y) of feedstocks composition versus UV-curing time were characterized. We evaluated various phenomenological models reported in the literature for predicting the critical yield shear strength (y*) required to obtain a paste structure for a certain aspect ratio. Knowing y* would help to determine the shortest time needed for UV illumination. Applying the model that best fitted to our experimental results, we developed a processing guideline that from specified magnetic permeability and dimensions of a ferrite core, would prescribe the needed SLED and the minimal UV curing time for printing. The guideline was demonstrated by the successful fabrication of tall ferrite inductor cores commonly found in power converters. The main contributions of this study are listed below: 1. Designed, formulated, and characterized ferrite feedstock that not only has functionality for power electronics applications but is also compatible with a direct extrusion type 3D printer. The feedstock can be made into ferrite cores with relative permeability ranging from 10 to 500 which are much higher than those of soft ferrite feedstocks currently reported elsewhere. The packing densities of 950℃ sintered ferrite cores made from the feedstock can be as high as 95%. With the Hyrel 30M 3D-printer, the smallest nozzle orifice diameter that the feedstock can be extruded from is 0.42 mm. We demonstrated printing of the feedstock into a cylinders with a height of 18 mm and an aspect ratio of 3 without slumping issue. 2. Identified the effects of materials and processing variales on 4 major considerations of the ferrite feedstock including maximizing sintered packing density, tailoring permeability, print-line resolution, and achievable dimensions of the printed feedstock without slumping. A deeper understanding of the mechanisms of how the variables affect main properties of the feedstock was provided. 3. Provided a preparation guideline of the ferrite feedstock that prescribe feedstock formulation and UV illumination time per print-layer from the target relative permeability and dimension of a ferrite core. / Doctor of Philosophy / To reduce the size of power electronic devices, applying novel designs of ferrite magnetic components (inductors and transformers) is a promising method. While conventional fabrication methods cannot fabricate novel designs of ferrite magnetic components that have odd or intricate geometries, additive manufacturing (AM) has the potential. One big challenge in 3D printing ferrite magnetic components is the lack of compatible and functional ferrite materials as printers' feedstock. This work focuses on developing ferrite feedstock for 3D printing ferrite magnetic components and providing a guideline for formulating ferrite feedstock by studying the effects of materials and processing parameters on major properties of the ferrite feedstock. The ferrite feedstock should not only have the desired functionalities but also be suitable for printing. Major considerations and desired properties of the feedstock were discussed. Materials were selected to formulate the feedstock based on the desired properties. To develop a formulation guidance for the feedstock, the effects of materials and processing variables on the major properties of ferrite feedstock were studied. The studies included the following 4 aspects: 1. the effects of materials fractions in the feedstock and the post-printing sintering temperature of the feedstock on maximizing magnetic permeability; 2. the effect of additives in the feedstock on tailoring permeability; 3. the effect of feedstock rheology on print-line resolution; 4. the effect of materials fraction and ultraviolet light illumination time on achievable aspect ratio of printed feedstock.

Magnetic components such as inductors and transformers are generally the largest circuit elements in switch-mode power systems for controlling and processing electrical energy. To meet the demands of higher conversion efficiency and power density, there is a growing need to simplify the process of fabricating magnetics for better integration with other power electronics components. The potential benefits of additive manufacturing (AM), or more commonly known as three-dimensional (3D) printing technologies, include shorter lead times, mass customization, reduced parts count, more complex shapes, less material waste, and lower life-cycle energy usage—all of which are needed for manufacturing power magnetics. In this work, an AM technology for fabricating and integrating magnetic components, including the design of manufacturing methodology and the development of the feedstock material, was investigated. A process flow chart of additive manufacturing functional multi-material parts was developed and applied for the fabrication of magnetic components. One of the barriers preventing the application of 3D-printing in power magnetics manufacturing is the lack of compatible and efficient magnetic materials for the printer's feedstock. In this work, several magnetic-filled-benzocyclobutene (BCB) pastes curable below 250 degree C were formulated for a commercial multi-material extrusion-based 3D-printer to form the core part. Two magnetic fillers were used: round-shaped particles of permalloy, and flake-shaped particles of Metglas 2750M. To guide the formulation, 3D finite-element models of the composite, consisting of periodic unit cells of magnetic particles and flakes in the polymer-matrix, was constructed. Ansoft Maxwell was used to simulate magnetic properties of the composite. Based on the simulation results, the pastes consisted of 10 wt% of BCB and 90 wt% of magnetic fillers—the latter containing varying amounts of Metglas from 0 to 12.5 wt%. All the pastes displayed shear thinning behavior and were shown to be compatible with the AM platform. However, the viscoelastic behavior of the pastes did not exhibit solid-like behavior, instead requiring layer-by-layer drying to form a thick structure during printing. The key properties of the cured magnetic pastes were characterized. For example, bulk DC electrical resistivity approached 107 Ω⋅cm, and the relative permeability increased with Metglas addition, reaching a value of 26 at 12.5 wt%. However, the core loss data at 1 MHz and 5 MHz showed that the addition of Metglas flakes also increased core loss density. To demonstrate the feasibility of fabricating magnetic components via 3D-printing, several inductors of differing structural complexities (planar, toroid, and constant-flux inductors) were designed. An AM process for fabricating magnetic components by using as-prepared magnetic paste and a commercial nanosilver paste was developed and optimized. The properties of as-fabricated magnetic components, including inductance and DC winding resistance, were characterized to prove the feasibility of fabricating magnetic components via 3D-printing. The microstructures of the 3D-printed magnetic components were characterized by Scanning-electron-microscope (SEM). Results indicate that both the winding and core magnetic properties could be improved by adjusting the formulation and flow characteristics of the feed paste, by fine-tuning printer parameters (e.g., motor speed, extrusion rate, and nozzle size), and by updating the curing profile in the post-process. The main contributions of this study are listed below: 1. Developed a process flow chart for additive manufacturing of functional multi-material components. This methodology can be used as a general reference in any other research area targeting the utilization of AM technology. 2. Designed, formulated and characterized low-temperature curable magnetic pastes. The pastes are physically compatible with the additive manufacturing platform and have applications in the area of power electronics integration. 3. Provided an enhanced understanding of the core-loss mechanisms of soft magnetic materials and soft magnetic composites at high frequency applications. / Ph. D.