| dc.description.abstract | Mobile additive manufacturing (AM) is a promising concept to overcome logistic barriers ensuring continuous and quick supply of parts directly at the site of interest. AM has the ability to produce complex parts directly according to a computer design, on site and without requiring tools or expensive maintenance. Raw material for printing the parts is the only addition making storage requirements and efforts minimal. Despite these exciting prospects, current available machines are not properly assessed for their performance in the field, on mobile platforms. This investigates the impacts of mobile operation on the most widely employed AM technology, Fused Deposition Modelling (FDM). It is shown how to overcome challenges and deviation from the norm and ensuring mobile AM with minimal adaptions to existing concepts.
Enabling mobile additive manufacturing is approached with a literature study on commercially available motion compensating platforms, expected influence from sea states and ship motion considerations establishing a theoretical framework of the project and defining key issues and potentially promising pathways for successful realization.
Based on this, a field trial was conducted onboard a coast guard vessel where varying gravitational pull, accelerations and vibrations related to vessel motion were measured on different places around the FDM machine. Dogbone test specimens made with four different print strategies were manufactured at different sea states the vessel was exposed to. The forced impacts of sudden anchor release and abrupt maneuvers were also evaluated against specimen geometry and mechanical properties. After the field trial, the geometric appearance and mechanical properties of sea prints were compared to land printed and injection moulded specimens.
Elastic modulus measured from both land and sea print vary between 1600-2400MPa depending on print strategy and cause of failure. Similar variation was obtained when measuring tensile strength ranging from 23,3-33,7MPa. The average difference observed between land and sea printed specimens show a tensile strength decrease of 6% for parts printed at sea. However, the same difference between sea and land prints are lower than the deviation observed within one batch. Heterogeneous layup in the interior caused specimens to delaminate and density was measured to 10% lower than injection moulded specimens. Crazings were observed in a distinct stress pattern showing about 13 stripes perpendicular to the tension direction. The pattern seems to be related to part geometry.
At the conditions employed in this work, the FDM print does not deviate from the norm in mobile operation. However, larger angles and higher accelerations could have an impact. This is possible when operating on similar or other vessels at higher sea states. Therefore, this thesis includes detailed consideration on the generalizability of the results. Design loads of other vessels were calculated according to standards from Det Norske Veritas (DNV). Also, the mobile operation of Selective Laser Sintering, a powder based and more delicate technology was considered. Potential compensating mechanisms were identified by means of Quality Function Deployment (IPM model) identifying one particular passive solution with a structure allowing angular movement close to the center of rotation to the build platform. This concept is believed most suitable to counteract identified and expected impacts of mobile AM operation at sea in the future.
This interdisciplinary work draws from material science, process development and metrology leading to the early stages of a sound product development. This work may set the path for mobile AM operation of different technologies on different vessels and sea states, providing goods on demand and on site in a reasonable time and effort at all logistic benefits AM is envisioned to provide. | en |
