Additive Manufacturing of Soft Polysiloxane-based Bio-structures with Heterogeneous Properties
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This thesis is concerned with the development of novel additive manufacturing (AM) systems and methodologies for high speed fabrication of complex material-graded silicone structures with controllable internal features consistently. To this end, two AM systems were developed, each pertaining to a specific phase of silicone rubber. The first system integrates material extrusion and material jetting AM systems. This system is designed to process the paste-like silicone rubbers at high viscosity levels (> 400,000 mPa.s at 10 1/s). In this system, the outer frame of each layer is made by extruding a highly uniform silicone strand at 5 mm/s printhead velocity. Once the perimeter is laid down on the substrate or the previous layer, a piezoelectric-based printhead with a translational speed of over 100 mm/s covers the internal section of layer by depositing uniform droplets of silicone at predefined locations. The printing parameters for both extrusion and jetting techniques were tuned using statistical optimization tools in order to minimize the surface waviness of printed parts. The optimized surface waviness values obtained are 8 μm and 3 μm for jetting and extrusion, respectively. Moreover, parts with solid density of over 99% and mechanical performance similar to the bulk material were manufactured by tailoring the rheology of silicone ink. A combination of powder-bed binder-jetting (PBBJ) system and micro-dispensing material extrusion form the second hybrid AM system. The three-dimensional (3D) shape forming of silicone powder is made possible for the first time using this system. The tomography results for the fabricated parts reveal a porous structure (~ 8% porosity). This AM process is introduced as a the proof-of-concept. The porosity of structures can be tuned by improving the silicone binder delivery method so that binder droplets with pico-liter volumes can be dispensed. The characterization techniques used for materials and additively manufactured parts include confocal-laser profilometry for investigating the surface quality of printed parts, differential scanning calorimetry (DSC) for investigating the curing mechanism of heat-curable silicone inks, Fourier transform infrared (FTIR) spectroscopy for controlling the curing kinetics and surface cohesion of UV-curable silicones, dynamic mechanical analysis (DMA) tests for tuning the rheological properties of silicone inks under different shear stresses, rheometry for establishing the viscosity threshold for jetting of silicone inks at different temperatures, scanning electron microscopy (SEM), particle size analysis, and powder rheometry for establishing guidelines for the size, shape, cohesiveness, flow, and shear stress resistance of silicone powders, uniaxial tensile test, tearing test, and durometry for identifying the mechanical characteristics of 3D printed parts, and computed-tomography (CT) scanning for quantifying the porosity of parts. The systems and fabrication methods introduced in this research, with high commercialization readiness levels, were concluded to have great impact on the manufacturing of functionally-graded complex bio-structures. This has been validated through high speed fabrication of multiple heterogeneous bio-structures. Moreover, the proposed techniques can be used for the fabrication of other silicone-based products.
Cite this version of the work
Farzad Liravi (2018). Additive Manufacturing of Soft Polysiloxane-based Bio-structures with Heterogeneous Properties. UWSpace. http://hdl.handle.net/10012/13057