Process Planning and Control for Functionally Graded Material Fabrication using Freeze-Form Extrusion Fabrication

Using multiple materials in additive manufacturing technologies is critical for building parts with functionally gradient geometries. In order to achieve a desired material gradient, an advanced process planning and control system is required. This paper details the development of a process planning method and control system for functionally graded material fabrication using a triple extruder Freeze-form Extrusion Fabrication (FEF) system including motion code generation, extruder dynamic modeling and control, and composition gradient control. The effect that extruding multiple materials from a single orifice via static mixing has on the time delay of the resulting mixture is taken into account for path planning, and this factor is incorporated into integrating motion codes with extrusion commands. The effectiveness of the proposed system is demonstrated by fabricating three-dimensional parts with desired gradient compositions using multiple materials

Process planning and control of functionally graded parts using freeze-form extrusion fabrication

Freeze-form Extrusion Fabrication (FEF) is an additive manufacturing technology that is capable of fabricating complex three-dimensional parts. FEF works by depositing an aqueous-based colloidal ceramic or metal paste in a layer-by-layer fashion below the freezing point of the aqueous medium as to rapidly freeze the paste. The FEF machine in the present study is equipped with three syringes and is capable of mixing each paste in a desired composition ratio by using an inline static mixer. Compensation for the transport delay caused by the static mixer is necessary; therefore, an algorithm was developed to apply a one-dimensional (1D) composition gradient to monolithic parts, adjusting the plunger velocities to account for the transport delay. Control of extrusion-based additive manufacturing techniques is difficult due to the uncertainties of the paste properties such as entrapped air bubbles, inhomogeneity, and inconsistency of the paste rheology from batch to batch. Other challenges are present such as starting and stopping extrusion on demand (EOD) and steady-state velocity control of a coupled triple extruder system. These issues have been addressed with the development and implementation of a hybrid extrusion force-velocity controller --Abstract, page iv

Paste development and co-sintering test of zirconium carbide and tungsten in Freeze-form Extrusion Fabrication

Ultra-high temperature ceramics are being investigated for future use in aerospace applications due to their superior thermo-mechanical properties, as well as oxidation resistance, at temperatures above 2000°C. However, their brittle properties make them susceptible to thermal shock failure. Components fabricated as functionally graded materials (FGMs) can combine the superior properties of ceramics with the toughness of an underlying refractory metal by fabricating graded composites. This paper discusses the grading of two materials through the use of a Freeze-form Extrusion Fabrication (FEF) system to build FGMs parts consisting of zirconium carbide (ZrC) and tungsten (W). Aqueous-based colloidal suspensions of ZrC and W were developed and utilized in the FEF process to fabricate test bars graded from 100%ZrC to 50%W-50%ZrC (volume percent). Following FEF processing the test bars were co-sintered at 2300°C and characterized to determine their resulting density and micro-structure. Four-point bending tests were performed to assess the strength of test bars made using the FEF process, compared to test bars prepared using conventional powder processing and isostatic pressing techniques, for five distinct ZrC-W compositions. Scanning electron microscopy (SEM) was used to verify the inner structure of composite parts built using the FEF process --Abstract, page iii

Flow-based fabrication: An integrated computational workflow for design and digital additive manufacturing of multifunctional heterogeneously structured objects

Structural hierarchy and material organization in design are traditionally achieved by combining discrete homogeneous parts into functional assemblies where the shape or surface is the determining factor in achieving function. In contrast, biological structures express higher levels of functionality on a finer scale through volumetric cellular constructs that are heterogeneous and complex. Despite recent advancements in additive manufacturing of functionally graded materials, the limitations associated with computational design and digital fabrication of heterogeneous materials and structures frame and limit further progress. Conventional computer-aided design tools typically contain geometric and topologic data of virtual constructs, but lack robust means to integrate material composition properties within virtual models. We present a seamless computational workflow for the design and direct digital fabrication of multi-material and multi-scale structured objects. The workflow encodes for and integrates domain-specific meta-data relating to local, regional and global feature resolution of heterogeneous material organizations. We focus on water-based materials and demonstrate our approach by additively manufacturing diverse constructs associating shape-informing variable flow rates and material properties to mesh-free geometric primitives. The proposed workflow enables virtual-to-physical control of constructs where structural, mechanical and optical gradients are achieved through a seamless design-to-fabrication tool with localized control. An enabling technology combining a robotic arm and a multi-syringe multi nozzle deposition system is presented. Proposed methodology is implemented and full-scale demonstrations are included

Adaptive meshing for finite element analysis of heterogeneous materials

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Modeling and Visualization of Multi-material Volumes

The terminology of multi-material volumes is discussed. The classification of the multi-material volumes is given from the spatial partitions, spatial domain for material distribution, types of involved scalar fields and types of models for material distribution and composition of several materials points of view. In addition to the technical challenges of multi-material volume representations, a range of key challenges are considered before such representations can be adopted as mainstream practice

Additive Manufacturing: Product Development Process Optimization Through CAD-CAM Integration

Die Verbreitung von 3D-Druck-Anwendungen im Bereich der Home- und Office-User führt zu einer gesellschaftlichen und medialen Fokussierung aller Technologien zur additiven Bauteilherstellung. Auch für die professionelle Anwendung dieser Technologien als Fertigungsverfahren werden die Möglichkeiten als grenzenlos beschrieben. Bei weitergehender Auseinandersetzung wird jedoch schnell festgestellt, dass sich additive Fertigungsverfahren zwar prinzipiell zur Herstellung von Produk-ten eignen, eine umfassende Einbindung in bekannte Betriebs- und Entwicklungsab-läufe jedoch noch nicht gegeben ist. Ziel der Arbeit ist es, eine umfassende CAD-CAM-Prozesskette für additive Fertigungsverfahren zu entwickeln. So sollen durch bessere Integration die Akzeptanz, Effizienz und Qualität des Produktentwicklungsprozesses gesteigert werden. Dazu wird ein Ansatz zur Erweiterung gängiger 3D-CAD-Systeme entwickelt. Hiermit sollen die für die additive Fertigung typischen Eigenschaften direkt bei der Bauteilgestaltung verfügbar gemacht werden. Die Integration resultiert letztendlich in der Bereitstellung von Schichtdaten im eigens entwickelten Schichtdatenformat Additive Manufacturing Layer File Format (AMLF). Die Umsetzung erfolgt durch umfassende Nutzung von Systems Engineering Methoden. Als Demonstrator für die Erfassung von Anforderungen und die Beschreibung von Teillösungen wird die gekühlte Leitschaufel einer Gasturbine gewählt.The growing use of 3D printing applications in the home and office environment increases media coverage of the related additive manufacturing technologies. In this regard, the possibilities for the professional utilization of these technologies are de-scribed as limitless. However, a closer look quickly reveals that additive manufacturing technologies are in principle suitable for manufacturing whereas a full integration in the known development processes is not given yet. Therefore, the aim of this work is the description of a comprehensive CAD-CAM-process chain for additive manufacturing. As a result a better acceptance, efficiency and quality of the product devel-opment process should be achieved. For this purpose, an approach for the enhancement of standard 3D-CAD-systems is developed. This approach provides additive manufacturing specific properties and features during the part design process, which eventually results in layer data that is exchanged with the self-developed Additive Manufacturing Layer File Format (AMLF). The implementation is carried out by the use of systems engineering methods. For an extended requirements review and the description of partial solutions, a cooled stationary blade of a gas turbine is chosen as demonstrator

A hierarchical representation for heterogeneous object modeling

A hierarchical representation for heterogeneous object modeling is presented in this paper. To model a heterogeneous object, Boundary representation is used for geometry representation, and a novel Heterogeneous Feature Tree (HFT) structure is proposed to represent the material distributions. HFT structure hierarchically organizes the material variation dependency relationships and is intuitive in modeling different types of material gradations. Based on the HFT structure, a recursive material evaluation algorithm is proposed to dynamically evaluate the material compositions at a specific location. Such a hierarchical representation guarantees complex material gradations and the user's design intent can be intuitively represented. Example heterogeneous objects modeled with this scheme are provided and potential applications are discussed. © 2004 Elsevier Ltd. All rights reserved.link_to_subscribed_fulltex