Is the production of metal parts using fused filament fabrication technology a viable option for the navy?

Abstract

Additive manufacturing (AM) presents a possibility to enhance the endurance of the naval ships and their ability to conduct operations. This thesis aims to present the advantages and the challenges one faces with the production of metal parts through the 3D printing method fused filament fabrication (FFF). Implementing AM techniques in various applications would make it necessary to estab lish standards to qualify and certify parts to ensure their reliability, especially under real istic cyclic loading conditions. A rotating bending fatigue test was therefore performed on test specimens printed in 316 stainless steel, with the intention of getting a rough S-N curve and identifying the printed material’s endurance limit. Fused filament fabrication is based on layer-by-layer manufacturing, and defects like poor adhesion, voids, porosity and shifted layers can occur. The defects can be difficult to notice and can lower the properties of the material drastically. Implementing FFF parts can therefore be difficult in industries where reliability and repeatability is crucial. The printed specimens suffered from poor adhesion between layers and twisted during the sintering process which involves heat treatment. Due to limited time and resources, it was only possible to print five specimens. The results were very inconsistent, and some tests were deemed unusable. None of the specimens could withstand a lot of cycles. At most 58200 cycles at 23,7 MPa and 5700 cycles at 47,4 MPa, which is very little com pared to for example stainless steel manufactured with selective laser melting, another AM method, which has an endurance limit of about 250 MPa. The main impression of the technology is that there are many variables and parameters that can affect the quality of the metal prints, and the maturity of the technology is not at the level where it can offer reliability and repeatability. Nevertheless, it is a promising technology. An alternative would be to print parts in reinforced composites which is widely researched, and already a focus area in the Norwegian Navy. Selective laser melt ing is also a technology worth looking into for additive manufacturing of metal.