Fundamental study of printing accuracy in Fused Deposition Modelling for bioinspired micro-structured surfaces

Abstract

The use of micro- and nanostructured surfaces has been explored as a new strategy to enable special surface functions in a variety of areas such as wettability control, anti biofouling, optical properties, tribology studies, and adhesion resistance. Many manufacturing methods can be applied for producing structured surfaces, including lithographic techniques, femtosecond laser machining or single point diamond turning. However, the cost has often been a critical barrier for the fabrication of functional surfaces on a mass scale. 3D printing techniques have recently emerged as a viable technology due to low material consumption, and high energy efficiency. Among these, Fused Deposition Modelling (FDM) provides a simpler manufacturing process and a more cost-effective method than other prominent 3D printing techniques. Despite the constant improvements in the resolution of this method, FDM still has the disadvantage of excessive extrudate expansion, limiting its application in precision manufacturing of functional structured surfaces. This work aims to develop a novel manufacturing method based on FDM for the fabrication of functional microstructures on thermoplastic polymers in a more cost effective manner with high throughput on very large scales, which potentially could be applied in the fabrication of bioinspired functional surfaces. For this purpose, the study first assesses the manufacturing accuracy of FDM by measuring the die swell effect of extrudate PLA filaments under varied working conditions in terms of extrusion temperatures (170 ⁰C – 210 ⁰C), printing speeds (10 mm/s – 80 mm/s), layer heights (0.10 mm – 0.40 mm) and nozzle sizes (0.20 mm – 0.40 mm). Different cooling methods are also applied in the printing process to suppress the die swell effect and therefore improve the manufacturing accuracy. By revealing the limitations of conventional theoretical models for predicting filament die swell in FDM process, a numerical model based on the level-set technique is developed to predict FDM extrudate die swell under different extruding conditions. This simulation method is also applied for studying the expansion of patterned structures during the extrusion process. The functions of structured surfaces are demonstrated by enhancing the wettability of a variety of polymers, including polyvinyl chloride (PVC), polyethylene 1000 (PE 1000), polypropylene copolymer (PP), and polytetrafluoroethylene (PFTE). It has been found that materials initially exhibiting common wettability properties (θ ≈ 90°) can exhibit “superhydrophobic” behaviour (θ ˃ 150°).