Alternate slicing and deposition strategies for Fused Deposition Modelling

Huang, Bin
Singamneni, Sarat
Diegel, Olaf
Neitzert, Thomas
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Doctor of Philosophy
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Auckland University of Technology

Fused deposition modelling is one of the most widely used rapid prototyping processes, considering the relative simplicity, availability, and ease of use. The proliferation of numerous systems at all possible price ranges led to a more widespread usage recently. A semisolid polymer such as acrylonitrile butadiene styrene (ABS) is deposited line-by-line, to build three dimensional objects in layers. Being capable of desk-top manufacturing, the process finds wide application in a variety of situations, be it making a mould for the rapid production of an industrial tool or the production of models for preoperative planning of complex cranial reconstructive surgery.

While these are predominantly prototyping applications, fused deposition modelling is capable of direct production of end-use parts and believed to be a possible replacement for injection moulding in specific applications. However, there are shortcomings such as inferior material attributes, flat layer deposition resulting in poor surface and part qualities, and undesirably higher number of layers in specific cases leading to high production times, which need to be resolved before realising the full potential of the process.

Attempts are made in the past by means of varying raster orientations, adaptive flat layer and even curved layer slicing and deposition schemes to overcome some of the shortcomings with fused deposition modelling. While stair case effects can be minimised to varying degrees by adaptive flat layers, mechanical properties are plausibly enhanced by curved layers, due to continuity in fibres and the possible elimination of inter-layer weaknesses. Further, the mechanism of material deposition and the mechanics of subsequent consolidation involve time and temperature dependent inter-strand and inter-layer sintering. Overall, the internal meso-structure is characterised by the partly fused polymer strands and the intertwining air gaps.

Research efforts in different directions, attempting improvements in materials as well as deposition techniques as evident in the literature, allowed some progress towards betterment. Although these improvements, especially in slicing algorithms led to significant progress in FDM processing, the part surface quality and geometric accuracy are still a major concern. Reducing build time and increasing part surface quality are two factors that contradict each other. Though proclaimed to be a solution to both, practical implementation of adaptive slicing has been limited and there is very little understanding of the typical influences of speed and time of printing on the mechanics of material consolidation and the ensuing meso-structures. Curved layer slicing on the other hand evolved as a means of improving surface quality and fibre continuity, but can only be effective in certain regions, close to curved outer surfaces of specific solid models.

Considering all these aspects, process enhancements are envisioned in fused deposition modelling, through identification of proper combinations of different slicing and deposition schemes together with appropriate raster orientations. This forms the basis for the current research, envisioning better solutions, combining different slicing and deposition strategies, targeting the most favourable meso-structures in order to achieve the best mechanical and surface qualities for a given part.

Theoretical and experimental evaluation of the mechanics of adaptive slicing and raster orientation effects need to be undertaken first, in order to understand the underlying principles governing the typical aspects of fused deposition modelling. Development of mathematical algorithms and practical implementation schemes will follow next, considering different slicing and deposition strategies, evaluating their abilities both individually and in combinations. Based on the results, different approaches will be integrated into an overall selection algorithm to develop the best combination of slicing and raster orientation schemes for processing different zones of specific components with given print orientations.

The analytical and experimental evaluations on adaptive slicing and the ensued results established that the inter-road and inter-layer coalescence depends on the filament size as well as the sintering time allowed for a unit length of deposition. Evidently, a proper adjustment of filament size, print speed and total time of printing will be essential to realise the true benefits of adaptive slicing. Raster angle orientation is found to significantly influence the overall characteristics of materials built layer-by-layer. Practical implementation and experimental results showed curved layer printing to be effective in improving the surface quality as well as the part strength as a result of the fibre continuity. Slanting side surfaces and projecting finer details in specific solid models are sufficiently resolved using adaptive flat and curved layer slicing. The integrated alternative slicing approaches performed well developing appropriate slicing schemes in different regions of specific solid models. Overall, different approaches help overcome different shortcomings of fused deposition modelling, but a combination of several possible alternatives is usually the best solution for a given part. Due consideration must be given to the internal mechanics and the resulting meso-structures in order to establish the best combination of the alternative slicing and deposition schemes available for fused deposition modelling.

Fused Deposition Modelling , Additive Manufacturing , Adaptive Slicing
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