Investigation of objective-driven slicing in multi-axis extrusion based additive manufacturing processes

Abstract

This Doctoral Research has been dedicated towards the advancement of multi-axis Material Extrusion (ME) technology where the manufacturing of parts involves the orthogonal deposition of material along freeform, 3-dimensional layers, conversely to conventional 3-axis Material Extrusion where the part is approximated through a plurality of only horizontal, planar layers. This transition from 2D to 3D space in which the layers span, enables for a vast increase in freedom in the spatial arrangement of layers that constitute a part, and consequently, its final properties. While in conventional ME the control a user has over the layer generation process is largely represented by the choice of part orientation and layer height, in multi-axis ME the shape of each and all layers themselves can also be controlled. However, with the increase in liberty of the process design, is there a direct necessity in understanding how to select a certain layer arrangement over another? How does one pick a specific slicing strategy if there is conceptually infinite possible solutions to manufacture the same part? It is exactly this curiosity that represents the core of this Doctoral Research; it hypothesises that desired part characteristics can be treated as objectives in the slicing process so that they help define a suitable layer arrangement. The design and planning of this research study have been defined following a detailed and systematic literature review with a wide research horizon of prior works that cover relevant multi-axis Additive Manufacturing (AM) topics not only in the family of Material Extrusion (ME), but also in a variety of other AM techniques dealing with metals, hybrid systems and novel, unconventional approaches. This resulted in the formulation of two research questions aimed at revealing the governing mechanism between the choice of a multi-axis slicing strategy and its effect on part’s accuracy and functionality accordingly. Case-study based research methodology was applied as a general, enveloping research approach. The obtained case-studies were then investigated combining qualitative and quantitative analysis ranging from observing part’s build and layer formation to an in-depth examination of numerical measurements data of a variety of part’s characteristics. The lack of a suitable processing tool required to practically implement layer-based, multi-axis ME by elaborating multi-axis slicing, toolpath formation and guidance of the manufacturing process, has prompted that an initial phase of this research addresses the development of such processing tool and its associated algorithms. Such a conglomerate of digital processing steps and a suitable manufacturing equipment were analysed in detail, developed, applied on a pilot study and ultimately established as a suitable framework for conducting the case-studies. The key research consisted in two parallel branches dedicated on investigating potential answers to the two research questions. Each of them included a two-step analysis method where first an isolated study provided the basis for establishing a slicing strategy aimed at part’s accuracy and functionality accordingly. In a second step, both of the established slicing strategies were applied on a fixed cross-comparative geometry, thus leaving the slicing strategy as the only independent variable in the studies. A total of eight case-studies were examined, with resulting evidence and data formulated in conclusions with respect to the research questions and hypothesis elaborated in this research.