Compensation zone approach to avoid print‐through 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 errors in its vertical dimension. In this paper, the “Compensation Zone approach” is presented to avoid this error.

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.

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.

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.

The errors in the vertical direction of a MPSLA build have been modeled for the first time. Compensation zone approach is a new concept.