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.

大规模熔融长丝制造（FFF）是增材制造领域中一个令人关注的增长领域，存在一些未解决的问题：材料的体积成本高，印刷过程慢，冷却速度低会导致结构不稳定或下垂。本文介绍了通过管材挤出（AMTEx）进行增材制造的概念，以此克服这些问题。

使用空心管代替固体挤压件意味着减少了材料使用量，并极大地改善了冷却性能，允许跨度超过400毫米而不会下垂。常规的自由形式挤出依赖于使用六轴机械手使挤出机喷嘴与刀具路径相切。已经发现，对印刷管内部的轻微加压允许从喷嘴轴线以大于90°的角度挤出而不会使管塌陷。除了减少自动打印冲突的可能性之外，这还允许使用传统的3D打印切片软件来生成打印机工具路径。它还开辟了使用常规三轴机床的潜力，大大提高了使用管子进行打印的适用性。