Direct digital manufacturing of ceramic parts is possible using focused ultraviolet (UV) light to pattern photopolymerizable ceramic suspensions. Ultimate spatial resolution is limited by the size of the UV beam. This dissertation focuses on other limiting factors. First, machine parameters and software can limit practical resolution of the processes. Second, if particle settling occurs, this can change the curing parameters. The effects of sedimentation on curing are modeled by combining the absorption model of sensitivity, the inhibitor exhaustion model for critical energy dose, and the Richardson-Zaki model of Stokes’ settling for monodisperse spheres. Finally, resolution can also be limited by “broadening”, where the width of a cured line is larger than the size of the UV beam.
To understand the physics of broadening, the effect of energy dose on the cure depth and cure width was determined. It is shown that the cure depth fits the expected Beer-Lambert behavior, where cure depth increases with the logarithm of energy and is described by the sensitivity and critical energy dose. The broadening can be described by the excess width, which fits a quasi-Beer-Lambert behavior as well. The absorption model predicts the effect of photoinitiator and dye on the cure depth, and this model can also be used to describe the excess width. Similarly, the inhibitor exhaustion model predictions for depth can be used to describe the excess width. The broadening depth is defined as the depth of cure when broadening begins. This is given by the cure depth where the energy dose is equal to the width critical energy dose. Below this broadening depth, no broadening is expected. It is shown that the broadening depth is proportional to the logarithm of the refractive index contrast between the ceramic powder and the liquids in solution. The role of contrast is understood in terms of the total path length in the absorption model using a random walk model. Tracing the photon paths using a hindered random walk model provides insight into the broadening behavior. Accounting for the angular distributions of scattering angles shows that broadening occurs at the expense of the cure depth.PHDMaterials Science and EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/96154/1/spgentry_1.pd
