Additive manufacturing via tube extrusion (AMTEx)

Abstract

Large scale Fused Filament Fabrication (FFF) is a growing area of interest within AM, with several unresolved problems: the volumetric cost of materials is high, the printing process is slow and low cooling rates result in unstable or sagging structures. This paper presents the concept of additive manufacturing via tube extrusion (AMTEx) as a means of overcoming these issues. Using hollow tubes in place of solid extrusions means material use is reduced and cooling properties are vastly improved, allowing spans in excess of 400 mm without sag. Conventional freeform extrusion relies on the use of six-axis robots to orientate the extruder nozzle tangentially to the toolpath. It was found that slight pressurisation of the inside of printed tubes allowed extrusion at more than 90° from the nozzle axis without tube collapse. Aside from reducing the possibility of robot-print collisions, this also allows the use of traditional 3D printing slicing software to generate printer toolpaths. It also opens the potential to use conventional three-axis machines, greatly increasing the applicability of printing with tubes. AMTEx tubes were found to be stronger under tension and bending compared to equivalent FFF parts and had significantly improved ductility.