An Experimental Investigation into the Dimensional Quality of the Material Extrusion Additive Manufacturing Process

Material Extrusion Additive Manufacturing (ME AM) also known as fused deposition modelling is a popular manufacturing process. It is seen as an attractive alternative to many conventional manufacturing techniques due to its cost effectiveness, ease of adoption, and the ability to produce complex geometries. However, it is commonly characterised by producing components that are of poor dimensional quality, particularly when it comes to part accuracy and geometry. Prior work has indicated that poor accuracy is primarily a function of printing parameter optimisation and flow behaviour during deposition. The majority of prior work in this domain has focused on complete artefacts. However, more recent landmark studies have demonstrated that poor dimensional accuracy occurs at a local strand level, which can significantly influence the macro dimensions and geometries of fabricated artefacts. These initial studies have presented some insights into the morphology of deposited strands, and how they are affected by printing parameter modulation. However, it is not yet fully known how sensitive the material extrusion process is, what magnitude of errors can occur at a local strand level, and how precise strand deposition is. Thus, this Thesis experimentally investigated the dimensional qualities of the material extrusion additive manufacturing process at a local strand level. The first study examined the deposition of single and multiple strands using extreme printing parameter values. The influence of extreme parameters was significant, illustrating that the process is highly sensitive to parameter changes particularly at a local level. The central portion of deposited strands exhibited far less morphological variation than the starts and ends. Deposition at a local level demonstrated how complex parameter interactions are for influencing the morphologies of single and multiple strands. The second study experimentally investigated single and multiple strand deposition using default printing parameter values. It was established that slicer cross-sectional dimensional approximations were not representative of what was actually deposited. Multiple strand deposition highlighted the misalignment between strand layers in multiple strand stacks. The third study employed a novel etching method to characterise single strand deposition precision. Stand misalignments and displacements relative to the nozzle position were significant and recurrent. High speed imaging established that lateral displacements were due to the intrinsic and unpredictable filament flow behaviour which are presently not correctable. Displacements in strands’ starts and ends raised questions about the prevalence of system hysteresis. The fourth and final study developed and employed a novel analysis technique to investigate if system hysteresis causes strands’ starts and ends displacements. Although hysteresis was detected in one of the machines, displacements were significantly affected by printing parameter values and poor adhesion. The cause of the hysteresis was not entirely certain, and it is difficult to determine if it was a mechatronic phenomenon or due to filament flow. It was concluded that material extrusion additive manufacturing accuracy and precision is a function of strand geometry, lateral and longitudinal position, which are influenced by machine design, processes parameters, and material. However, the patterns of influence are not easily predicted or consistent between the errors. As a result, optimisation is exceptionally challenging. Future work should focus on in-situ observation of flow behaviour in the nozzle.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2023

Author dc:creator

• Golab, Mark

Advisor dc:contributor.advisor

• Moultrie, James

• material extrusion additive manufacturing
• Fused deposition modelling
• Filament behaviour
• Printing parameters
• Dimensional accuracy

Licence

• https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/596f2164-4c49-4cb0-961f-a84ce10b179d/download
• https://www.rioxx.net/licenses/all-rights-reserved/

Language dc:language

eng

Author Identifier

0000-0002-7729-1841

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/371506