Abstract
Recent advances in large-scale thermoplastic additive manufacturing (AM), using fused deposition modelling (FDM), have shown that the technology can effectively produce large aerospace tools with common feed stocks, costing 2.3 $/kg, such as a 20% carbon-filled acrylonitrile butadiene styrene (ABS). Large-scale additive manufacturing machines have build-volumes in the range of cubic meters and use commercially available pellet feedstock thermoplastics, which are significantly cheaper (5–10 $/kg) than the filament feedstocks for desktop 3D printers (20–50 $/kg). Additionally, large-scale AM machines have a higher material throughput on the order of 50 kg/h. This enables the cost-efficient tool production for several industries. Large-scale 3D-printed tooling will be computerized numerical control (CNC)-machined and -coated, to provide a surface suitable for demolding the composite parts. This paper outlines research undertaken to review and improve the adhesion of the coating systems to large, low-cost AM composite tooling, for marine or infrastructure composite applications. Lower cost tooling systems typically have a lower dimensional accuracy and thermal operating requirements than might be required for aerospace tooling. As such, they can use lower cost commodity grade thermoplastics. The polymer systems explored in the study included polypropylene (PP), styrene-maleic anhydride (SMA), and polylactic acid (PLA). Bio-based filler materials were used to reduce cost and increase the strength and stiffness of the material. Fillers used in the study included wood flour, at 30% by weight and spray-dried cellulose nano-fibrils, at 20% by weight. Applicable adhesion of the coating was achieved with PP, after surface treatment, and untreated SMA and PLA showed desirable coating adhesion results. PLA wood-filled composites offered the best properties for the desired application and, furthermore, they have environment-friendly advantages.
Highlights
Large-scale tooling for low-cost marine or infrastructure composite applications is fabricated using a multi-step process, using a welded steel frame, plywood sheathing, a machined polystyrene substrate covered with epoxy fiberglass, and an epoxy-based tooling paste for the final computerized numerical control (CNC) machining, sanding, and the final coating application
Surface treatments for 3D-printing materials could improve the adhesion of the final coating used for marine direct composite tool construction
The adhesion promoter led to a pull-off strength that is not as high as the one obtained after the plasma treatment
Summary
Large-scale tooling for low-cost marine or infrastructure composite applications is fabricated using a multi-step process, using a welded steel frame, plywood sheathing, a machined polystyrene substrate covered with epoxy fiberglass, and an epoxy-based tooling paste for the final computerized numerical control (CNC) machining, sanding, and the final coating application. This is a complex and labor-intensive process. This research focusses on the surface treatment of low-cost filled polymer systems and the subsequent adhesion of a common surface coating, for composite tooling. Following a more practical approach, the pull-off strength of the applied coating was determined by a dolly test [14,15]
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