Christopher B. Williams

Additive manufacturing (AM) and nanotechnology: promises and challenges

Purpose – This paper aims to provide a review of available published literature in which nanostructures are incorporated into AM printing media as an attempt to improve the properties of the final printed part. The purpose of this article is to summarize the research done to date, to highlight successes in the field, and to identify opportunities that the union of AM and nanotechnology could bring to science and technology.Design/methodology/approach – Research in which metal, ceramic, and carbon nanomaterials have been incorporated into AM technologies such as stereolithography, laser sintering, fused filament fabrication, and three‐dimensional printing is presented. The results of the addition of nanomaterials into these AM processes are reviewed.Findings – The addition of nanostructured materials into the printing media for additive manufacturing affects significantly the properties of the final parts. Challenges in the application of nanomaterials to additive manufacturing are nevertheless numerous.Re...

Multiple-Material Topology Optimization of Compliant Mechanisms Created Via PolyJet Three-Dimensional Printing

Compliant mechanisms are able to transfer motion, force, and energy using a monolithic structure without discrete hinge elements. The geometric design freedoms and multimaterial capability offered by the PolyJet 3D printing process enables the fabrication of compliant mechanisms with optimized topology. The inclusion of multiple materials in the topology optimization process has the potential to eliminate the narrow, weak, hingelike sections that are often present in single-material compliant mechanisms and also allow for greater magnitude deflections. In this paper, the authors propose a design and fabrication process for the realization of 3-phase, multiple-material compliant mechanisms. The process is tested on a 2D compliant force inverter. Experimental and numerical performance of the resulting 3-phase inverter is compared against a standard 2-phase design.

Enhancing usability in CITIDEL: multimodal, multilingual, and interactive visualization interfaces

We describe four usability-enhancing interfaces to CITIDEL aimed at improving the user experience and supporting personalized information access by targeted communities. These comprise: a multimodal interaction facility with capability for out-of-turn input, interactive visualizations for exploratory analysis, a translation center exposing multilingual interfaces, as well as traditional usability enhancements. Pilot studies demonstrate the resulting improvements in quality, as measured across a number of metrics.

Online Real-Time Quality Monitoring in Additive Manufacturing Processes Using Heterogeneous Sensors

The objective of this work is to identify failure modes and detect the onset of process anomalies in additive manufacturing (AM) processes, specifically focusing on fused filament fabrication (FFF). We accomplish this objective using advanced Bayesian nonparametric analysis of in situ heterogeneous sensor data. Experiments are conducted on a desktop FFF machine instrumented with a heterogeneous sensor array including thermocouples, accelerometers, an infrared (IR) temperature sensor, and a real-time miniature video borescope. FFF process failures are detected online using the nonparametric Bayesian Dirichlet process (DP) mixture model and evidence theory (ET) based on the experimentally acquired sensor data. This sensor data-driven defect detection approach facilitates real-time identification and correction of FFF process drifts with an accuracy and precision approaching 85% (average F-score). In comparison, the F-score from existing approaches, such as probabilistic neural networks (PNN), naive Bayesian clustering, support vector machines (SVM), and quadratic discriminant analysis (QDA), was in the range of 55–75%.

Designing Platforms for Customizable Products and Processes in Markets of Non-Uniform Demand

The foremost difficulty in making the transition to mass customization is how to offer product variety affordably. The answer to this quandary lies in the successful management of modularity and commonality in the development of products and their production processes. While several platform design techniques have emerged as a means to offer modularity and commonality, they are limited by an inability to handle multiple modes of offering variety for multiple design specifications. The Product Platform Constructal Theory Method (PPCTM) is a technique that enables a designer to develop platforms for customizable products while handling issues of multiple levels of commonality, multiple product specifications, and the inherent tradeoffs between platform extent and performance. The method is limited, however, by its inability to handle multiple design objectives and its reliance on the assumption that demand in the market is uniform for each product variant. The authors address these limitations in this study by infusing the utility-based compromise decision support problem and demand modeling techniques. The authors further augment the PPCTM by extending its use to a new domain: the design of process parameter platforms. The augmented approach is illustrated through a tutorial example: the design of a product and a process parameter platform for the realization of a line of customizable cantilever beams.

Polymer structure-property requirements for stereolithographic 3D printing of soft tissue engineering scaffolds

This review highlights the synthesis, properties, and advanced applications of synthetic and natural polymers 3D printed using stereolithography for soft tissue engineering applications. Soft tissue scaffolds are of great interest due to the number of musculoskeletal, cardiovascular, and connective tissue injuries and replacements humans face each year. Accurately replacing or repairing these tissues is challenging due to the variation in size, shape, and strength of different types of soft tissue. With advancing processing techniques such as stereolithography, control of scaffold resolution down to the μm scale is achievable along with the ability to customize each fabricated scaffold to match the targeted replacement tissue. Matching the advanced manufacturing technique to polymer properties as well as maintaining the proper chemical, biological, and mechanical properties for tissue replacement is extremely challenging. This review discusses the design of polymers with tailored structure, architecture, and functionality for stereolithography, while maintaining chemical, biological, and mechanical properties to mimic a broad range of soft tissue types.

A Functional Classification Framework for the Conceptual Design of Additive Manufacturing Technologies

Many different additive manufacturing (AM) technologies enable the realization of prototypes and fully-functional artifacts. Although very different in solution principle and embodiment, significant functional commonality exists among the technologies. This commonality affords the authors an opportunity to propose a new classification framework for additive manufacturing technologies. Specifically, by following the systematic abstraction approach proposed by the design methodology of Pahl and Beitz, the authors first identify the working principles of each AM process. A morphological matrix is then employed to functionally present these principles such that commonalities between processes can be identified. In addition to using it as a means of classifying existing processes, the authors present the framework as a tool to aid a designer in the conceptual design of new additive manufacturing technologies. The authors close the paper with an example of such an implementation; specifically, the conceptual design of a novel means of obtaining metal artifacts from three-dimensional printing.

An Investigation of Key Design for Additive Manufacturing Constraints in Multimaterial Three-Dimensional Printing

The PolyJet material jetting process is uniquely qualified to create complex, multimaterial structures. However, key manufacturing constraints need to be explored and understood in order to guide designers in their use of the PolyJet process including (1) minimum manufacturable feature size, (2) removal of support material, (3) survivability of small features, and (4) the self-supporting angle in the absence of support material. The authors use a design of experiments (DOE) approach to identify the statistical significance of geometric and process parameters and to quantify the relationship between these significant parameters and part manufacturability. The results from this study include the identification of key variables, relationships, and quantitative design thresholds necessary to establish a preliminary set of design for additive manufacturing (DfAM) guidelines for material jetting. Experimental design studies such as the one in this paper are crucial to provide designers with the knowledge to ensure that their proposed designs are manufacturable with the PolyJet process, whether designed manually or by an automated method, such as topology optimization (TO).

An exploration of binder jetting of copper

Purpose – The purpose of this paper is to explore the use of binder jetting to fabricate high-purity copper parts. The ability to fabricate geometrically complex copper shapes would have implications on the design and manufacture of components for thermal management systems and structural electronics. Design/methodology/approach – To explore the feasibility of processing copper via binder jetting, the authors followed an established material development process that encompasses powder selection and tuning process parameters in printing and thermal cycles. Specifically, the authors varied powder size and sintering cycles to explore their effects on densification. Findings – Three differently sized copper powders were successfully printed, followed by sintering in a reducing atmosphere. It was found that a 15-μm-diameter powder with a sintering cycle featuring a 1,080°C maximum temperature provides the most dense (85 per cent) and pure (97 per cent) final copper parts of the parameters tested. Research limi...

Topology Optimization for Additive Manufacturing: Considering Maximum Overhang Constraint

Additively manufactured components often require temporary support material during the 3D printing process. In the case of polymer material process such as Fuse Deposition Modeling (FDM), the support material can be dissolved away. However in the case of metals in a selective laser melting (SLM) process, the support and component material are one in the same. Since the support structure adds both material cost and post-processing cost to every component printed, it is desired to limit or completely eliminate the need for such material. As such, it is proposed to take advantage of the maximum printable overhang angle (the angle at which the AM process requires no support material) by harnessing topology optimization as the design engine. This is accomplished through a topology optimization projection scheme, in which the angle constraint is imposed through a Heaviside projection and not applied as an explicit constraint. Solutions to two standard topology optimization problems are included and show good agreement with the overhang constraint.