Master of Science / Material extrusion is a common form of 3D printing that has historically been limited to producing prototypes, models, and low load-bearing parts. This is primarily because parts are manufactured layer-by-layer, resulting in poor adhesion along the build direction, and machines struggle to print with high-strength polymers, which tend to shrink significantly as they cool. However, one way to address these limitations is to use fiber-reinforced materials in combination with multi-axis deposition strategies. In material extrusion, embedded fibers will align themselves along the deposition path, providing structural, thermal, and chemical improvements. Multi-axis toolpathing can enable the deposition of this fiber-filled material in full 3D along a part's expected stress paths. This is possible using a complex kinematic system like an industrial robot arm that can rotate the angle of the tool relative to the part as it is printing. The objective of this work was to develop and test a tool capable of multi-axis continuous carbon fiber reinforcement, which required a dedicated cutting mechanism to shear the fiber at the end of each deposition path, control over the amount of fiber used, and a slender tool profile to avoid collisions during multi-axis printing. The findings of this work revealed that while the use of continuous carbon fiber further reduced the adhesion between deposition paths, it substantially improved the strength of the part along them. To validate the multi-axis capability of the system, a toolpath was generated for a curved tensile bar. The results showed that the continuous carbon fiber multi-axis toolpath resisted a load 820.57% higher than an XY-planar sliced part printed with traditional filament, confirming the effectiveness of the presented approach.
Multi-axis motion can also be used for avoiding support material requirements. In traditional 3-axis material extrusion, steep overhanging features often require additional, sacrificial material to be printed underneath. This leads to longer print times, more material waste, and a poor surface finish left behind on the final part. To minimize the amount of support material required, various techniques have been explored, including changing the toolpath, part geometry, or material processing parameters. However, none of these techniques have been successful in eliminating the need for supports entirely. A promising approach to address this issue is multi-axis material extrusion, where the angle of the printing tool and the direction of the layers can be precisely controlled during the printing process. This technique can be used to ensure that the tool is always extruding material onto a well-supported surface, rather than over thin air. However, research to date has not yet fully explored how the range of achievable overhang features changes as the tool is rotated. To address this knowledge gap, this work used an industrial robot arm equipped for material extrusion to investigate the relationship between tool angle, build direction, and achievable overhang threshold. The results showed that the same overhang limitations that exist in the XY plane will rotate with the tool and are unaffected by gravitational forces. These findings provide valuable insights for advancing the use of multi-axis material extrusion in the production of complex and intricate 3D objects without the need of supports.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/115677 |
| Date | 06 July 2023 |
| Creators | Beaumont, Kieran Deane |
| Contributors | Mechanical Engineering, Williams, Christopher Bryant, Bortner, Michael J., Raeymaekers, Bart, Komendera, Erik |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International, http://creativecommons.org/licenses/by-nc-sa/4.0/ |
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