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

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

On the aesthetic significance of imprecision in computational design: Exploring expressive features of imprecision in four digital fabrication approaches

Precision of materialized designs is the conventional goal of digital fabrication in architecture. Recently, however, an alternative concept has emerged which refashions the imprecisions of digital processes into creative opportunities. While the computational design community has embraced this idea, its novelty results in a yet incomplete understanding. Prompted by the challenge of the still missing knowledge, this study explored imprecision in four digital fabrication approaches to establish how it influences the aesthetic attributes of materialized designs. Imprecision occurrences for four different digitally aided materialization processes were characterized. The aesthetic features emerging from these imprecisions were also identified and the possibilities of tampering with them for design exploration purposes were discussed. By considering the aesthetic potentials of deliberate imprecision, the study has sought to challenge the canon of high fidelity in contemporary computational design and to argue for imprecision in computation that shapes a new generation of designs featuring the new aesthetic of computational imperfection

Modulated extrusion for textured 3D printing

This research utilises a Fused Deposition Modelling 3D Printer to investigate the aesthetics of 3D printing and it's broader applications. The presented research re-evaluates the 3D printer as a tool to manipulate materials, as opposed to a machine that discretely reproduces digital models at a fine resolution. The research questions the utility of automation, and attempts to find a level that permits materially expressive modes of fabrication. The exploration of aesthetics has uncovered a variety of unexpected textures and interesting material properties that may have wider use. For instance, rigid plastic has been extruded and manipulated finer than the extrusion nozzle diameter, which confers flexibility and fabric like qualities to the printed object. The discovered techniques for 3D printed aesthetics are reproducibly reliable and can be incorporated back into orthodox digital-model driven fabrication

An overview of rapid prototyping technologies using subtractive, additive and formative processes

Ovaj rad opisuje metodologiju za primenu brze izrade prototipova primenom subtraktivnih, aditivnih i formativnih tehnologija na osnovu STL fajlova. Tehnologije brze izrade prototipova uključuju digitalni lanac informacija CAD/CAM /CNC, do nivoa koji omogućava uspešnu realizaciju fizičkih modela koristeći novu tehnologiju, dodavanjem, oduzimanjem i oblikovanjem materijala. U radu su razmatrane uobičajene tehnologije brze izrade prototipova, za koje je predložena generalizovana metodologija za njihovu primenu. Pokazane su i mogućnosti za verifikaciju programa pre same izrade modela. Metodologija je verifikovana na konkretnim primerima izrade izabranih delova koristeći tehnologije oduzimanja, dodavanja materijala sloj po sloj, i izrade kalupa (dodavanjem materijala) za livenje modela od silikona.This paper describes methodology for application of a rapid prototyping using subtractive, additive and formative technology based on STL files. Rapid prototyping technology includes using of a digital information chain CAD/CAM/CNC to a level which allows the successful realization of the physical models based on new technologies by adding, subtracting and molding material. The paper discusses about the usual technologies for rapid prototyping, for which a generalized methodology for their application has been proposed. The possibilities for program verification prior to the realization of the model were also shown. The methodology is verified on real examples of making selected parts. Used technologies are subtracting and adding material layers, layer by layer, and mold making (by adding material) for molding the silicone model

Design for metal fused filament fabrication (DfMF3) of Ti-6Al-4V alloy.

Additive manufacturing (AM) offers unmatchable freedom of design with the ability to manufacture parts from a wide range of materials. The technology of producing three-dimensional parts by adding material layer-by-layer has become relevant in several areas for numerous industries not only for building visual and functional prototypes but also for small and medium series production. Among others, while metal AM technologies have been established as production method, their adoption has been limited by expensive equipment, anisotropy in part properties and safety concerns related to working with loose reactive metal powder. To address this challenge, the dissertation aims at developing the fundamental understanding required to print metal parts with bound metal powder filaments using an extrusion-based AM process, known as metal fused filament fabrication (MF3). MF3 of Ti-6Al-4V has been investigated, owing to significant interest in the material from aerospace and medical industries on account of their high strength-to-weight ratio, excellent corrosion resistance and biocompatibility. To investigate the material-geometry-process interrelationship in MF3 printing, the current work looks into the process modeling and simulation, the influence of material composition and resulting characteristics on printed part properties, effects of printing parameters and slicing strategies on part quality, and part design considerations for printability. The outcome of the work is expected to provide the basis of design for MF3 (DfMF3) that is essential to unlocking the full potential of additive manufacturing. Moreover, the layer-by-layer extrusion-based printing with the highly filled material involves several challenges associated with printability, distortion and dimensional variations, residual stresses, porosity, and complexity in dealing with support structures. Currently, a high dependency on experimental trial-and-error methods to address these challenges limits the scope and efficiency of investigations. Hence, the current work presents a framework of design for MF3 and evaluates a thermo-mechanical model for finite element simulation of the MF3 printing process for virtual analyses. The capability to estimate these outcomes allows optimization of the material composition, part design, and process parameters before getting on to the physical process, reducing time and cost. The quantitative influence of material properties on MF3 printed part quality in terms of part deformation and dimensional variations was estimated using the simulation platform and results were corroborated by experiments. Also, a systematic procedure for sensitivity analysis has been presented that identified the most significant input parameters in MF3 from the material, geometry and process variables, and their relative influence on the print process outcome. Moreover, feasible geometry and process window were identified for supportless printing of Ti-6Al-4V lattice structures using the MF3 process, and an analytical approach has been presented to estimate the extrudate deflection at the unsupported overhangs in lattice structures. Finally, the design and fabrication of Ti-6Al-4V maxillofacial implants using MF3 technology are reported for the first time confirming the feasibility to manufacture patient-specific implants by MF3. The outcome of the work is an enhanced understanding of material-geometry-process interrelationships in MF3 governing DfMF3 that will enable effective design and manufacturing