Architectured materials with rationally designed geometries could be used to create mechanical metamaterials with unprecedented or rare properties and functionalities. Here, we introduce “shape-matching” metamaterials where the geometry of cellular structures comprising auxetic and conventional unit cells is designed so as to achieve a pre-defined shape upon deformation. We used computational models to forward-map the space of planar shapes to the space of geometrical designs. The validity of the underlying computational models was first demonstrated by comparing their predictions with experimental observations on specimens fabricated with indirect additive manufacturing. The forward-maps were then used to devise the geometry of cellular structures that approximate the arbitrary shapes described by random Fourier’s series. Finally, we show that the presented metamaterials could match the contours of three real objects including a scapula model, a pumpkin, and a Delft Blue pottery piece. Shape-matching materials have potential applications in soft robotics and wearable (medical) devices.

An extrusion based additive manufacturing (EAM) technique, recently became competitive for the rapid production of metals and ceramics components. This is made possible by extruding the metal or ceramic material in solid powder form, mixed with a binder, i.e. an expendable viscous fluid, which is removed from the part after 3D printing. The strength of these technologies relies on the large design freedom allowed by and by the cost efficiency advantage vs. alternative metal additive manufacturing processes based on high energy beams, e.g. laser/electron beam.EAM of metals and ceramics is not yet widespread, and the published scientific and technical literature is rapidly growing, but still less extensive than the literature on FDM of plastics or SLM of metals. This paper aims at filling this gap. Fused Deposition Modeling (FDM) and Powder Injection Molding (PIM) are identified as preceding or enabling technologies for EAM. This paper systematically reviews all the aspects of feedstock extrusion-based AM processes used for production of complex shaped parts. Then, the unique characteristics and advantages of the process are discussed, with respect to materials and process steps. The key process parameters are explained to illustrate the suitability of the process for diverse domains of applications.

A new extrusion-based additive manufacturing technique is described in this paper together with the main components of the machine capable of carrying out the process. Innovative characteristics of the machine are the fixed extrusion head and the workpiece moving thanks to a 5-axis parallel kinematics handling system, allowing the capability of inclining the part during the material deposition and consequently avoiding support structures. The extrusion head and nozzle have been designed in order to be able to extrude high viscosity mixtures with low polymeric content. Preliminary tests prove that a good final density can be obtained after de-binding and sintering and that it is possible to achieve a good bonding of extruded and deposited wires in case of AISI 630 stainless steel

The elastic properties of mechanical metamaterials are direct functions of their topological designs. Rational design approaches based on computational models could, therefore, be used to devise topological designs that result in the desired properties. It is of particular importance to independently tailor the elastic modulus and Poisson's ratio of metamaterials. Here, we present patterned randomness as a strategy for independent tailoring of both properties. Soft mechanical metamaterials incorporating various types of patterned randomness were fabricated using an indirect additive manufacturing technique and mechanically tested. Computational models were also developed to predict the topology-property relationship in a wide range of proposed topologies. The results of this study show that patterned randomness allows for independent tailoring of the elastic properties and covering a broad area of the elastic modulus-Poisson's ratio plane. The uniform and homogenous topologies constitute the boundaries of the covered area, while topological designs with patterned randomness fill the enclosed area

Abstract. The design of a new additive manufacturing (AM) system based on extrusion and 3D deposition of a mixture of metal (or advanced ceramic) powder and polymeric binder is described in this paper. The proposed system is totally innovative in terms of combination of deposited work material, extrusion system (head and nozzle), and deposition work table, which is based on a 5-axes parallel kinematics machine (PKM). The extrusion head and nozzle have been designed in order to be able to extrude high viscosity mixtures with low polymeric content. The 5-axes PKM is aimed at obtaining a good surface quality of the deposited work and reducing the need for supports during deposition. After the deposition, the material is de-binded and sintered to nearly the density of the solid material ascast. The design and kinematics of the machine and especially the PKM table is described in this paper, the main design issues are discussed and some preliminary extrusion and sintering results are presented.