Nicholas A. Meisel

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.

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).

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.

A procedure for creating actuated joints via embedding shape memory alloys in PolyJet 3D printing

Additive manufacturing’s layer-by-layer fabrication approach allows the user to access the entire volume of the part throughout the build process. This allows for the embedding of functional components and actuators to enable the fabrication of complex systems in a single process. A process for the embedding of shape memory alloy actuating wire within direct PolyJet 3D printed parts is presented in this article. A series of “Design for Embedding” considerations are presented for achieving successful and repeatable embedding results. These considerations include guide channel design, design of shape converters for irregularly shaped elements, and design of wire fixation points. The embedding process is demonstrated with two case studies: a simple compliant joint specimen with a straight shape memory alloy wire and an antagonistic joint design with spring-shaped shape memory alloys. The process is characterized through an exploration of the potential for surface defects in the final specimens, as well as basic quantitative and qualitative evidence regarding performance of the final embedded actuators.

Exploring variability of orientation and aging effects in material properties of multi-material jetting parts

Purpose Understanding how material jetting process parameters affect material properties can inform design and print orientation when manufacturing end-use components. This study aims to explore the robustness of material properties in material jetted components to variations in processing environment and build orientation. Design/methodology/approach The authors characterized the properties of six different material gradients produced from preset “digital material” mixes of polypropylene-like (VeroWhitePlus) and elastomer-like (TangoBlackPlus) materials. Tensile stress, modulus of elasticity and elongation at break were analyzed for each material printed at three different build orientations. In a separate ten-week study, the authors investigated the effects of aging in different lighting conditions on material properties. Findings Specimens fabricated with their longest dimension along the direction of the print head travel (X-axis) tended to have the largest tensile strength, but trends in elastic modulus and elongation at break varied between the rigid and flexible photopolymers. The aging study showed that the ultimate tensile stress of VeroWhitePlus parts increased and the elongation decreased over time. Material properties were not significantly altered by lighting conditions. Research limitations/implications Many tensile specimens failed at the neck region, especially for the more elastomeric parts. It is hypothesized that this is due to the material jetting process approximating curves with a pixelated droplet arrangement, instead of curved contour as seen in other additive manufacturing processes. A new tensile specimen design that performs more consistently with elastomer-like materials should be considered. The aging component of this study is focused solely on polypropylene-like (VeroWhitePlus) material; additional research into the effects of aging on multiple composite materials is needed. Originality/value The study provides the first known description of orientation effects on the mechanical behavior of photopolymers containing varied concentrations of elastomeric (TangoBlackPlus) material. The aging study presents the first findings on how time affects parts made via material jetting.

Decision support for additive manufacturing deployment in remote or austere environments

Purpose Additive manufacturing (AM) can reduce the process supply chain and encourage manufacturing innovation in remote or austere environments by producing an array of replacement/spare parts from a single raw material source. The wide variety of AM technologies, materials, and potential use cases necessitates decision support that addresses the diverse considerations of deployable manufacturing. The paper aims to discuss these issues. Design/methodology/approach Semi-structured interviews with potential users are conducted in order to establish a general deployable AM framework. This framework then forms the basis for a decision support tool to help users determine appropriate machines and materials for their desired deployable context. Findings User constraints are separated into process, machine, part, material, environmental, and logistical categories to form a deployable AM framework. These inform a “tiered funnel” selection tool, where each stage requires increased user knowledge of AM and the deployable context. The tool can help users narrow a database of candidate machines and materials to those appropriate for their deployable context. Research limitations/implications Future work will focus on expanding the environments covered by the decision support tool and expanding the user needs pool to incorporate private sector users and users less familiar with AM processes. Practical implications The framework in this paper can influence the growth of existing deployable manufacturing endeavors (e.g. Rapid Equipping Force Expeditionary Lab – Mobile, Army’s Mobile Parts Hospital, etc.) and considerations for future deployable AM systems. Originality/value This work represents novel research to develop both a framework for deployable AM and a user-driven decision support tool to select a process and material for the deployable context.

Design and assessment of a 3D printing vending machine

Purpose – The purpose of this study/paper is to present the design and implementation of a novel vending machine concept based on desktop-scale extrusion additive manufacturing (AM). Due to cost, access to AM technologies at academic institutions tends to be limited to upper-level courses to support project-based coursework. However, with the decreasing cost of desktop-scale AM technology, there is potential to improve student access to such technologies and provide more opportunities for AM education. Design/methodology/approach – The authors present the design and implementation of an AM “vending machine” that is powered by desktop-scale extrusion-based AM systems. This system intends to provide students broad, unrestricted access to entry-level AM tools and promote informal learning opportunities. Findings – Student users of the AM vending machine are found to be primarily engineering majors at various levels in their studies. Manufactured parts are evenly split between functional and decorative parts,...

Evaluating the relationship between deposition and layer quality in large-scale additive manufacturing of concrete

ABSTRACT Scaling up additive manufacturing (AM) for automated building construction requires expertise from different fields of knowledge, including architecture, material science, engineering, and manufacturing to develop processes that work for practical applications. While concrete is a viable candidate for printing due to its common use in building, it raises important challenges in deposition due to the material deformation that occurs as concrete transitions from fresh to hardened states. This study aims to experimentally quantify the deformation of printed concrete layers under the influence of different processing variables, including layer thickness, printing orientation, and direction. A mixer-pump extrudes the material and an industrial 6-axis robotic arm, which provides various ranges of movement in different axes, layers the material. The results of this study can be used to develop a tool for predicting and accounting for the deformation of concrete layers during the AM process.