Compensation Zone Approach to Avoid Z Errors in Mask Projection Stereolithography Builds

Print-through results in unwanted polymerization occurring beneath a part cured using Mask Projection Stereolithography (MPSLA) and thus creates error in its Z dimension. In this paper, the "Compensation zone approach" is proposed to avoid this error. This approach entails modifying the geometry of the part to be cured. A volume (Compensation zone) is subtracted from underneath the CAD model in order to compensate for the increase in the Z dimension that would occur due to Print-through. Three process variables have been identified: Thickness of Compensation zone, Thickness of every layer and Exposure distribution across every image used to cure a layer. Analytical relations have been formulated between these process variables in order to obtain dimensionally accurate parts. The Compensation zone approach is demonstrated on an example problem.