Post-Additive Manufacturing Densification and Dimensional Stability of a Commercial Stereolithography Silica Resin

Fabricating green (unfired) ceramic powder compacts with complex geometry using stereolithography is well established. The advent of a low-cost professional SLA printer with a commercial ceramic resin offers designers an intriguing material choice. For engineering uses, however, it is necessary to quantitatively assess the evolution of microstructure as well as dimensional stability during post-AM densification. In pursuit of this, we designed a standard specimen based on a hollow cube, nominally 25 mm on an edge, with a wall thickness of 4 mm. The surfaces of the cubes were decorated with short cylinders, square prisms, and a square array of short pegs. The corners of the cube were chamfered. This design permits a number of independent dimensional measurements to be readily obtained. Results include: variability of dimensions, systematic deviations from average, evidence of discontinuous delamination, and some devitrification. The sensitivity of results to some geometric features, e.g., wall thickness is reported. In a separate set of experiments, the feasibility of green state joining of subcomponents using the stereolithography resin and UV lamps was tested with a simple investment casting mold that was created. Despite qualitative success with the trial mold, engineering use of the resin appears limited. Planar accuracy of green prints to model in the X and Y directions were most precise coming in at 99.7% to the nominal design, and the Z direction was 98.1%. Post-fire shrink was observed to be around 14%, and deviation from squareness was >1%. Cracking was the biggest issue with the cube prints, and several trials were conducted in efforts to understand and eliminate the cracking. Of all the variables tested, part orientation on the build platform and strategic use of fillets were the most effective in preventing cracks. An inverted cube was successfully produced without showing horizontal post-fire cracks.