# Geometric Benchmarking of Metal Material Extrusion Technology: A Preliminary Study
## 1 Introduction  
Additive manufacturing (AM) is the general term used to address technologies that successfully join material layer upon layer to create physical objects as specified by 3D model data [1]. The progressive addition of material offers the possibility to overcome limitations typical of subtractive and plastic deformation processes, enabling great design freedom while avoiding the need for tooling and molds. This process optimizes resource usage by minimizing material waste, since the material is selectively added only where necessary [2]. Such findings are contributing to the widespread use of AM to produce functional components in many industrial fields, including aerospace [3], electronics [4], robotics [5], thermal management [6], automotive [7], and medical [8]. Particular interest is drawn by AM techniques, such as powder bed fusion (PBF) and direct energy deposition (DED), which are capable of selectively processing layers of metal powder and obtaining physical and mechanical properties comparable to those achieved through traditional technologies [9]. However, the competitiveness of such techniques is hindered by high energy consumption, slow build-up rates, and high costs of both the equipment and materials. Porosity defects formation during rapid solidification also represents a crucial challenge that deleteriously impacts material properties [10; 11]. An economical alternative to the metal AM technologies mentioned above is represented by metal material extrusion (metal-MEX), also known as fused deposition modeling (FDM), since extrusion-based machines are cost-effective. Widely used for the production of polymeric parts, MEX has been adapted to metal components manufacturing by developing highly filled composite filaments. Such filaments have a complex multi-material formulation resulting from the homogenous mixture of sinterable metal powders and a polymeric binder system. The latter usually comprises a main binder component toprovide flowability to the filament, a backbone to supply shape retention, and additives to disperse the filler particles, thus preventing agglomeration and phase separation [12]. The content of metal particles in the filament strongly influences the properties of manufactured parts, resulting in reduced tensile strength and increased thermal conductivity [13; 14]. In addition, the size, morphology, and composition of the particles also affect the mechanical and flow properties of the filament [15]. Due to the composite nature of the filament, metal parts are obtained only at the end of an indirect multi-step process, often referred to as shaping-debinding-sintering [16]. First, the extrusive shaping step is required to fabricate green parts using the MEX machine. Most of the binder system is then removed through catalytic [17], solvent, and/or thermal debinding [18]. The resulting highly porous brown parts (same volume, lower mass) are then subjected to a sintering treatment, performed below the melting temperature of the filler metal. The thermal cycle drives the formation of interparticle bonds, which grow, resulting in porosity reduction and near-total densification [12]. However, the impossibility of achieving full densification of sintered parts is responsible for developing anisotropic shrinkage, as proved by several studies [19; 20]. Dimensional variations and distortions induced by thermal processing in metal-MEX ought to be compensated to ensure the design compliance of the parts, especially when manufacturing thin structures. The cost and energy required by post-printing treatments are subjected to the economy of scale by maximizing the number of components to be treated [21; 22]. Performing geometrical and dimensional inspections is therefore essential to improve quality and to increase the confidence of industries in AM products [23]. Geometric capabilities, uncertainties, and limitations of AM processes can be quantitatively evaluated by fabricating and analyzing geometric benchmark test artifacts (GBTAs).