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  • Additive manufacturing of metals via material extrusion : Ph.D. program in Design, Manufacturing, and Operation Engineering
    Sadaf, Mahrukh
    Material extrusion (MEX), also termed as fused filament fabrication (FFF), is a promising technique that can offer an economical alternative to manufacture metal parts with complex geometry. The ... method is based on a thermoplastic organic binder filled with metallic powder to produce feedstock filaments. Filaments are employed to shape components in similar machines as for the commercial FDM of plastics. The organic binders are removed from the feedstock, called debinding, and further sintering to get the fully densified solid components. The implication of filaments necessitates flexible, stiff, and low viscous feedstocks, which is a challenge because of the high amount of metallic powder (≥ 50 vol.%). Various MEX feedstocks have been reported in the literature. Most commercially available feedstocks are debound in two steps, catalytic or solvent debinding and thermal debinding. 316L stainless steel, copper, and AlSi10Mg feedstocks were developed according to the morphological, rheological, and mechanical properties and the debinding practices criteria. The feedstock homogeneity had a great impact on the processing and debinding performance as the improper material distribution leads to defects. Low-density polyethylene was used as a backbone in the feedstock formulation. Moreover, other feedstock formulations based on polypropylene and high-density polyethylene as a backbone binder were also developed to study the effect on the properties of final metallic components. Various other additives like stearic acid, waxes, and plasticizers were also added in the feedstock formulation to enhance the wettability among powder-binder, avoiding phase separation and agglomeration. The effect of MEX parameters on the printed green parts was determined. It was observed that tuning the extrusion temperature, reducing the speed of the printing, and using the high volumetric material flow led to good quality printed parts with negligible defects. Also, to compare the dimensional stability of the MEX components, a highly commercially available technique, metal injection molded (MIM), was used. The processing parameters were optimized to produce good quality MIM parts. Further, the effect of processing parameters on debinding and sintering was studied. The effect of MEX parameters on the mechanical properties of the final parts was evaluated, and the results were compared with MIM sintered parts. The results of this thesis give an understanding of the role of filaments in MEX and heat treatment like debinding and sintering. Moreover, the influence of the printing parameters on the processability and mechanical properties was established. Current results can provide detailed insight into the development of a new binder system, enhance the understanding of the mechanism happening throughout the manufacturing of highly densified metals via MEX, and offer unique views in metals processing by other additive manufacturing and conventional technologies based on similar materials. Based on the knowledge of current research, there is a strong possibility of using a recycled polymer as an organic binder in the future, in view of a low environmental impact process.
    Type of material - dissertation ; adult, serious
    Publication and manufacture - Roma : [M. Sadaf], 2022
    Language - english
    COBISS.SI-ID - 122141955

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