Deflectometry for surface inspection and shape fidelity analysis for manufacturing and polishing of safety spectacle molds

Work in hazardous zones with possible chemical, thermic or mechanical injuries requires protection with safety spectacles, produced by injection molding techniques. Despite the high importance of optical quality, molds are rarely tested before or during the injection process. The purpose of this study was to implement 3D phase measuring deflectometry (PMD) for shape fidelity tests of (bi)spherical and fullform mold surfaces. The setup is based on a PMD sensor (3D-Shape GmbH, Erlangen, Germany) equipped with 3 cameras and a 5 axis positioning stage. Analysis of the object’s surface was reviewed by GOM Inspect (GOM mbH, Braunschweig, Germany). Eight molds of a bispherical safety spectacle and two spherical fullform molds were polished, measured and corrected through accurately described form revision. Target-actual comparisons and defined fit evaluations showed local groove, peaks and global shape deviations from -19µm to 30µm. The molds were repolished concerning the surface analysis. In conclusion, the setup allows shape characterization of molds before and after repolishing.