Functional and Optical Properties of Structured Surfaces in Additive Manufacturing: Technologies for appearance evaluation in the quality assurance of 3D-printed polymers

Abstract

Quality assurance of additively manufactured parts requires assessment of appearance and surface finish quality. Appearance investigation is a primary step to ensure that the manufactured parts meet the required structural, functional, and dimensional specifications, as well as possess the desired aesthetic qualities. Among the attributes considered when assessing an appearance are color, gloss, haze, translucency, texture, and surface finish. In advanced manufacturing, this process is particularly critical in industries where consumer perception and brand image are crucial, such as biomedical, automotive, aerospace, and consumer-oriented applications. This thesis explores studies concerning structured surfaces in the additive manufacturing of polymers. During this project, the primary components of the manufacturing process were examined and considered, including materials, design, production, quality control, and optimization. Experimental and statistical analyzes were conducted to determine the optical and functional properties of the additively manufactured layers and how primary processing parameters affect additive manufacturing. A number of additive manufacturing (AM) machines were investigated, including Fused Filament Fabrication (FFF), Material Jetting (MJT), Stereolithography (SLA), and Selective Laser Sintering (SLS). PolyJet as an MJT technology was considered the specialization. Several conclusions were drawn from the investigations and findings are reported for further development of PolyJet technology. An optimization and enhancement method has been developed to improve the properties of the material and the appearance of the final parts over a more extended period. Several properties were considered, such as optical properties, mechanical properties, life cycle response, and implementation of digital materials used for prototyping, medical purposes, and harsh environmental applications. A long-term descriptive study examined the color appearance, tensile behavior, and glass transition temperature of MJT objects in weathering chambers. Specific challenges were identified, and solutions were proposed according to Taguchi analysis to meet the quality goal of advanced manufacturing. An extensive literature review was conducted to examine the surface characteristics of 3Dprinted objects with a particular focus on surface roughness. A comparative study has been conducted to determine the manufacturing factors influencing the lifetime, surface quality, and dimensional accuracy. Further investigations addressed these challenges, resulting in a comprehensive overview of the available AM techniques and identifying the most critical parameters influencing surface roughness. We have addressed the complexity of appearance assessment and the need for interpreting data and correlating them using multivariate statistical analysis. It has been discussed how printing parameters should be incorporated into advanced appearance modeling, taking into consideration that MJT objects possess complex appearances, are semi-translucent, and require a comprehensive study of their appearance. For instance, the build orientation and wedge angle determine whether we use cost-effective reflectance models, such as bidirectional reflectance distribution function (BRDF), or more sophisticated, accurate, and expensive models, such as bidirectional surface scattering distribution functions (BSSRDF), depending on the application requirements. In addition, it has been demonstrated that MJT is a promising technique that provides realistic objects that have very low appearance deficiencies, which is necessary for expanding the application of additive manufacturing. Many other aspects of appearance in additive manufacturing were examined in conceptual investigations, including gloss, haze, translucency, texture, and reflectance modeling. This led to a deeper understanding of total control over appearance during prototyping and design. An industry 4.0 manufacturing environment will rely heavily on the latter. Compared to the other studies examining optical properties, these investigations focused primarily on appearance behavior rather than general applications in optics or for mechanical purposes. The differences and challenges of these results are more relevant to human perception of appearance than laser-based applications in photonics