From 3D Models to 3D Prints: an Overview of the Processing Pipeline

Due to the wide diffusion of 3D printing technologies, geometric algorithms for Additive Manufacturing are being invented at an impressive speed. Each single step, in particular along the Process Planning pipeline, can now count on dozens of methods that prepare the 3D model for fabrication, while analysing and optimizing geometry and machine instructions for various objectives. This report provides a classification of this huge state of the art, and elicits the relation between each single algorithm and a list of desirable objectives during Process Planning. The objectives themselves are listed and discussed, along with possible needs for tradeoffs. Additive Manufacturing technologies are broadly categorized to explicitly relate classes of devices and supported features. Finally, this report offers an analysis of the state of the art while discussing open and challenging problems from both an academic and an industrial perspective.Comment: European Union (EU); Horizon 2020; H2020-FoF-2015; RIA - Research and Innovation action; Grant agreement N. 68044

Studying the cooling stage in fused filament fabrication

Fused Filament Fabrication (FFF) is one of the available techniques that is capable of producing parts by additive manufacturing, i.e., by depositing thin filaments of thermoplastic polymers or composites onto a support as a vertical series of horizontal 2D slices of a 3D part. This chapter approaches FFF from a phenomenological point of view, and then focus on the deposition and cooling stage. A code capable of predicting the evolution of temperature during deposition and until cooling is completed, as well as of the final bonding between filaments is presented. The tool is then used to enlighten the effect of major processing parameters on the quality of parts

Multi-Axis Multi-Material Fused Filament Fabrication with Continuous Fiber Reinforcement

Additive Manufacturing (AM) has become a well-recognized method of manufacturing and has steadily become more accessible as it allows designers to prototype ideas, products and structures unconceivable with subtractive manufacturing techniques for both consumer grade and industrial grade applications. Commonly used thermoplastics for 3D printing have properties that may not be sufficient to comply with the application’s certification requirements, or their performance is less than desirable for aerospace and other high performance applications. Additionally, additively manufactured parts have reduced mechanical properties in the build direction of the print, and are generally weaker than their equivalent injection-molded parts. Furthermore, Computer Aided Design and Manufacturing (CAD/CAM) tools have evolved together with the evolution of processes for subtractive and deformative based manufacturing methods, and ply-based additive composite manufacturing. For AM to gain more traction in industrial engineering environments, the process specific algorithms for AM need to be implemented in CAD/CAM software. There is therefore a need for reinforcement of both the material and the structures, and for proving the industrial capabilities of additive manufacturing, in particular fused filament fabrication, through a new set of processes that complement the existing design paradigm. A promising solution to the above mentioned problems of strength is using engineering thermoplastics and through the addition of continuous carbon fibers in the print. Unfortunately, engineering-thermoplastic impregnated continuous carbon fiber filaments for 3D printing do not exist due to the low demand and pure filament is currently only available for proprietary printers at steep prices. Additional strength increase in the inter-layer direction may come through the addition of local reinforcement deposited on an existing structure in the build direction, which implies stepping away from layer-by-layer manufacturing and manufacturing using true 3D deposition and toolpathing. This is only possible by exploiting the full benefits of a 6 or higher degree of freedom printing system. In this research, a KUKA robotic platform capable of motion with 6 degrees of freedom is used as a base to develop a multi-axis, industrial-scale 3d printer. Polyetherimide (PEI), an engineering thermoplastic sold under the Sabic brandname ULTEM 1000 was acquired in pellet form and extruded within tolerances into a usable 3D printing filament. ULTEM 1000-Continuous Carbon Fiber filament was developed by dissolving the ULTEM 1000 pellets in a solution bath and consequently pulling the carbon fiber through it. A specialized nozzle design and printing bed capable of going up the required processing temperatures was developed and integrated with the KUKA platform, for which specialized toolpathing software was written. The toolpathing software consists of two subsets: a slicing tool that allows multi-orientation slicing, and a translation parser which converts the G-code toolpath commands into KUKA-format KRL. The slicing tool uses Stereo lithography-format (STL) triangulated mesh files to generate slices of toolpathing for a geometry, which is then modified to add toolpathing for both global and local features with multi-orientation slicing techniques. In this way, compound objects can be sliced without the restrictions of common slicers. Designed for use with the broad range of capabilities of modern industrial robotics, a 6-axis directional reinforcement can thus be added to various types of base geometries. In addition to syntax modification, the translation parser also detects insignificant and collinear commands in the G-code and converts groups of points representing a discretized arc into a higher-order arc-command. Repeated sections in the code are also collapsed into a for-loop structure. This significantly reduces the file size and increases the accuracy of the toolpathing code. The in-house developed printer was used to print coupons for a multitude of ASTM tests to evaluate the mechanical performance, including longitudinal and transverse tensile and compression tests, shear and interlaminar shear tests. Specimen were also subjected to in-house Thermo-Gravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) tests to determine the chemical characteristics, and a range of other methods were used to identify fiber-volume ratios, void-volume ratios and surface quality of the pellets, filaments and printed parts. Furthermore, two configurations of the printer were assessed: one where the bed is the KUKA end effector and the nozzle is stationary, and one where the nozzle is the KUKA end effector and the bed is stationary. A prototype of a 7th axis, and initial toolpathing was added to the system to allow full rotational freedom expanding the robots operating envelope and complexity of the printed parts. Beyond the printer development, toolpathing development, material development and testing, several industrial components for funding partners were printed as a proof of concept and for marketing purposes, demonstrating the technology readiness of this process. The methods, processes and results discussed in this paper are developed with certification in aerospace in mind, and they show great promise for the implementation of functional additive manufacturing on 6 degree of freedom platforms in high-performance demanding industries

SFCDecomp: Multicriteria Optimized Tool Path Planning in 3D Printing using Space-Filling Curve Based Domain Decomposition

We explore efficient optimization of toolpaths based on multiple criteria for large instances of 3D printing problems. We first show that the minimum turn cost 3D printing problem is NP-hard, even when the region is a simple polygon. We develop SFCDecomp, a space filling curve based decomposition framework to solve large instances of 3D printing problems efficiently by solving these optimization subproblems independently. For the Buddha model, our framework builds toolpaths over a total of 799,716 nodes across 169 layers, and for the Bunny model it builds toolpaths over 812,733 nodes across 360 layers. Building on SFCDecomp, we develop a multicriteria optimization approach for toolpath planning. We demonstrate the utility of our framework by maximizing or minimizing tool path edge overlap between adjacent layers, while jointly minimizing turn costs. Strength testing of a tensile test specimen printed with tool paths that maximize or minimize adjacent layer edge overlaps reveal significant differences in tensile strength between the two classes of prints.Comment: Minor edits to incorporate reviewers' comments. Published in IJCG

Conformal 3D Material Extrusion Additive Manufacturing for Large Moulds

Industrial engineering applications often require manufacturing large components in composite materials to obtain light structures; however, moulds are expensive, especially when manufacturing a limited batch of parts. On the one hand, when traditional approaches are carried out, moulds are milled from large slabs or laminated with composite materials on a model of the part to produce. In this case, the realisation of a mould leads to adding time-consuming operations to the manufacturing process. On the other hand, if a fully additively manufactured approach is chosen, the manufacturing time increases exponentially and does not match the market’s requirements. This research proposes a methodology to improve the production efficiency of large moulds using a hybrid technology by combining additive manufacturing and milling tools. A block of soft material such as foam is milled, and then the printing head of an additive manufacturing machine deposits several layers of plastic material or modelling clay using conformal three-dimensional paths. Finally, the mill can polish the surface, thus obtaining a mould of large dimensions quickly, with reduced cost and without needing trained personnel and handcraft polishing. A software tool has been developed to modify the G-code read by an additive manufacturing machine to obtain material deposition over the soft mould. The authors forced conventional machining instructions to match those of an AM machine. Thus, additive deposition of new material uses 3D conformal trajectories typical of CNC machines. Consequently, communication between two very different instruments using the same language is possible. At first, the code was tested on a modified Fused Filament Fabrication machine whose firmware has been adapted to manage a milling tool and a printing head. Then, the software was tested on a large machine suitable for producing moulds for the large parts typical of marine and aerospace engineering. The research demonstrates that AM technologies can integrate conventional machinery to support the composite materials industry when large parts are required