Cold Spray Additive Manufacturing is a technology capable of mass manufacturing components with complicated geometry and coating substrates in hard-to-reach areas. In addition, cold spray also has the ability of conducting a green manufacturing process, with zero waste of renewable feed material, and zero gas and chemical emission. This paper investigates solely cold spray as an additive manufacturing technology with cork as the natural material. CFD results were used to predict the physical behavior of air and the cork particles. After unsuccessful coatings, final results showed that when moisture is added, cork is successfully cold sprayed, and agglomeration is experienced. Following these results, high speed camera and Hopkinson bar tests concluded that pressure is the only significant parameter that drastically effects the disposition quality of the cork coating. This is the first reported result of cork powder being cold sprayed, in addition to groundbreaking results of successfully coating an Aluminum substrate without a binder. Key words: cork, powder, additive manufacturing, natural materials, cold spray, binder, deposition efficiency, coating, high speed camera, Hopkinson bar.

To address the size limitation of the powder bed fusion system in additive manufacturing, the welding properties of 316L stainless steel manufactured by SLM 125HL are investigated by conducting hot ductility test and nil strength temperature (NST) test with a physical thermal mechanical simulator, Gleeble. In this study, the print orientations (Zdirection and XY-direction) and the laser patterns (stripe and checker board) are studied. In NST test, the orientation showed a statistical significance in NST: Z-direction was 1384°C and XY-direction was 1400°C. In hot ductility test, all of ductility curves show similar behaviors: hardening region, recrystallization region, and liquation region. The additively manufactured 316L shows poor ductility compared to wrought 316L stainless steel. Also, there is a noticeable difference in ductility between laser pattern. Finally, ductility after the thermal cycle shows higher than that before the thermal cycle. For the future recommendation, investigation on the interelayer temperatures and sigma phase determination should be conducted to confirm the hypotheses to explain the phenomena observed in this study.

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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Polymer powder bed fusion (PBF/P) is one of many additive manufacturing (AM) processes utilized for producing polymer parts from digital 3D models. AM is preferred over traditional manufacturing methods in many applications due to advantages including tool-less manufacturing, high geometric complexity, short lead times, and reduced material waste. However, many industries that stand to benefit the most from AM are limited in their ability to use AM parts in large part due to low confidence in AM part quality. Among the polymer AM processes, PBF/P processes show significant promise for these applications due to their comparatively high isotropy and mechanical properties. Due to the many process variables present in PBF/P, printing conditions can vary from print to print resulting in poor repeatability of physical properties in printed parts. Many approaches have been studied for addressing this issue such as modeling of print dynamics, print parameter optimization, and process control. However, PBF/P remains largely unutilized in applications where quality control and assurance are high priorities. This work presents a novel approach for in-situ process monitoring and control in PBF/P and is demonstrated for the large area projection sintering (LAPS) process. The method proposed in this study monitors the powder bed surface via visible light cameras and identifies critical steps in the melting process defined as optical melting states (OMSs). The relationship between print parameters, process signatures, and resulting physical properties are studied. This thesis shows that during melting, the changing surface geometry and optical properties of the powder bed can be effectively monitored with optical cameras and are strongly correlated with the final density and ultimate tensile strength (UTS) of the printed part. By implementing closed-loop OMS control, consistent physical properties can be obtained despite different processing conditions. While established methods of identifying the property plateau for other PBF/P processes are not effective for the LAPS process, such as energy density methods, OMS control has been shown to effectively achieve full density and UTS in LAPS parts while optimizing print time. However, OMS methods are limited in their ability to evaluate ductility and percent crystallinity.

Additive manufacturing (AM) is a general name used for production methodswhich have the capabilities of producing components directly from 3D computeraided design (CAD) data by adding material layer-by-layer until a final component is achieved. Included here are powder bed technologies, laminated object manufacturing and deposition technologies. The latter technology is used in this study.Laser metal deposition using powder as an additive (LMD-p) is an AM processwhich uses a multi-axis computer numerical control (CNC) machine or robot toguide the laser beam and powder nozzle over the deposition surface. Thecomponent is built by depositing adjacent beads layer by layer until thecomponent is completed. LMD-p has lately gained attention as a manufacturing method which can add features to semi-finished components or as a repair method. LMD-p introduce a low heat input compared to arc welding methods and is therefore well suited in applications where a low heat input is of an essence. For instance, in repair of sensitive parts where too much heating compromises the integrity of the part.The main part of this study has been focused on correlating the main processparameters to effects found in the material which in this project is the superalloy Alloy 718. It has been found that the most influential process parameters are the laser power, scanning speed, powder feeding rate and powder standoff distance and that these parameters has a significant effect on the dimensionalcharacteristics of the material such as height and width of a single deposit as wellas the straightness of the top surface and the penetration depth.To further understand the effects found in the material, temperaturemeasurements has been conducted using a temperature measurement methoddeveloped and evaluated in this project. This method utilizes a thin stainless steel sheet to shield the thermocouple from the laser light. This has proved to reduce the influence of the emitted laser light on the thermocouples.

In collaboration with Kongsberg Automotive, the thesis focuses on material selection and redesigning the shift fork for additive manufacturing using topology optimization. The shift fork is a component in the gear shifting mechanism in the automotive industry. The current shift fork at Kongsberg is manufactured from aluminum using die-casting. This design and material do not withstand huge dynamic loads in commercial vehicles. The material to withstand the loading conditions and is widely available across powder manufacturers is selected using the weighted properties method. The topology optimization of the design resulted in a 50 % reduction in mass. The shift fork's two legs undergo uneven load distribution due to eccentricity. The optimized models are simulated using Finite Element Analysis to validate the design. The optimized design is obtained such that the difference in displacement between both legs is within 50 %. Numerous metal powder manufacturers and 3D printing service providers were contacted to understand the current additive manufacturing market.

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