Co-authors​ :

 Maximilian Konstantin STROBEL (GERMANY), The Anh Dieter NGUYỄN (GERMANY), Swen ZAREMBA (GERMANY), Dr.Klaus DRECHSLER (GERMANY) 

Additive manufacturing allows for efficient and flexible production of tools for the aerospace composites industry. By using contour and near-net shape printing, material costs can be significantly reduced compared to conventional tool manufacturing from metals such as aluminum and steel. Extrusion-based processes are commonly used for large-scale mold manufacturing due to their scalability. Vacuum and pressure-assisted processes, such as Vacuum Assisted Resin Infusion or Resin Transfer Moulding, are frequently used to produce fiber composite components. A vacuum and gas-tight mold surface is crucial in this production process. Fused Filament Fabrication (FFF) results in microstructural inhomogeneities and porosity due to the layered structure and the placement of polymer strands side-by-side. Therefore, post-processing the surface of FFF-printed molds is essential. Milling, grinding, and sealing are performed laboriously by hand. An automated alternative is Thermo-Mechanical Smoothing (TMS), which was introduced by Taufik et al. in 2020. This method involves the automated application of a heated spherical geometry that is passed over the part, similar to conventional milling, locally melting the polymer and minimizing the stair-step effect. This work continues the development of a smoothing process that utilizes a 3D printer with an integrated thermo-mechanical smoothing unit. The first step involves analyzing the media permeability of FFF printed samples using the pressure rise method by varying parameters such as extrusion temperature, number of layers, and extrusion width. This method uses a vacuum pump to generate negative pressure in an enclosure separated from the ambient air by the test specimen. Microcracks and porosity can cause an increase in pressure, which can be measured to determine leakage. The samples are considered airtight if the pressure loss is less than 5 mbar/min. In the second step, test specimens are produced and subjected to thermo-mechanical smoothing. Different spherical smoothing geometries with diameters of 10 mm, 15 mm, and 20 mm are used. The varied process parameters, to make the surface impermeable to media are the smoothing temperature, the distance between the trajectories, and the trajectory speed. The polymer layer is melted at the surface during the smoothing process, which reduces the step effect and closes imperfections. It is demonstrated with micrographs of cross-sections, that the compaction of the TMS caused by pressure and temperature leads to a significant reduction in porosity. The post-processing step of smoothing enables in-situ sealing of printed molds, significantly reducing the need for additional materials and manual processing.