Compensation zone approach to avoid print-through errors in mask projection stereolithography builds

摘要

Purpose - Print-through results in unwanted polymerization occurring beneath a part cured using Mask Projection Stereolithography (MPSLA) and thus creates errors in its vertical dimension. In this paper, the "Compensation Zone approach" is presented to avoid this error. Design/methodology/approach - Compensation zone 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 simulated on a test part with a slanted down-facing surface. Findings - The simulation results show that the compensation zone approach can reduce print - through errors significantly. In addition, it has been demonstrated numerically that the approach can also alleviate the problem of stair stepping. Research limitations/implications - The derivations in the compensation zone approach are made with the following simplifying assumptions: exposure is additive; threshold model of resin cure is valid; the resin molecules underneath the part being cured are stationary; and the cleaning process can completely clean the part off the surrounding resin, due to these assumptions, the compensation zone model might require some calibration. Originality/value - The errors in the vertical direction of a MPSLA build have been modeled for the first time. Compensation zone approach is a new concept.