Appearance evaluation of digital materials in material jetting

Abstract

Material jetting (MJT) products have a high subjective appearance quality in additive manufacturing (AM). MJT objects are typically manufactured from multiple layers of semi-transparent photo resins to achieve the desired appearance. This study explores the optical properties of photopolymer plates in monolayer and bilayer combinations. The role of the white substrate as the background plate in bilayer configurations is discussed concerning appearance reproduction in MJT parts. For this purpose, spectral reflectance, transmittance, absorbance, color difference, and texture were investigated for MJT objects with different plate combinations. The primary digital materials in MJT were further investigated for haze, gloss, scattering variations, and their corresponding bidirectional reflectance distribution functions (BRDFs). The optical properties of the studied surfaces were then applied to three-dimensional (3D) models to illustrate the variation in visual appearance and texture. According to the results, it was inevitable to use a white background plate for color reproduction. Therefore, increasing the layer thickness did not improve color fidelity. Due to the role of microfacet normals in the surface texture, gloss, haze, and scattering, results followed the same analysis pattern but depended on the measurement direction.