Compliant mechanisms are able to transfer motion, force, and energy using a monolithic structure without discrete hinge elements. The geometric design freedoms and multimate rial capability offered by the PolyJet 3D printing process enables the fabrication o f com pliant 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 fabri cation process for the realization of 3-phase, multiple-material compliant mechanisms. The process is tested on a 2D compliant force inverter. Experimental and numerical per formance o f the resulting 3-phase inverter is compared against a standard 2-phase design.

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.

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).

No abstract