In this study, a novel low-cost polishing method for internal surface roughness reduction of additively manufactured components, developed for waveguide (WG) circuits operating in the millimeter frequency range is proposed. WG components fabricated using powder bed fusion (PBF) generally feature roughness of ten to fifty microns, which influences the increase of roughness-related conductor power losses having a major effect on the electrical performance of additively manufactured all-metal WGs. To improve and decrease the surface roughness of circuits fabricated using PBF, glass microbeads as an abrasive medium are proposed to be used in combination with a rotary tumbler. This technique allows the abrasive medium to efficiently penetrate internal long channels and cavities, having cross section dimensions in the range of sub-to a few millimeters. An experimental study was carried out on an example of WG sections and bandpass filters fabricated using PBF through selective laser melting (SLM), operating within the 8.2 to 40 GHz range. Polishing impact on both mechanical and electrical properties was studied showing surface roughness reduction by 18% and sixth order filter’s insertion loss reduction at 23 GHz by 40% after 24 h of tumbling with 300–400 $\mu$ m large glass microbeads.

In this paper, a low-cost method of 3D printed all-metal waveguide effective conductivity improvement is proposed and studied. The approach is a combination of internal surface polishing to reduce the roughness followed by coating a high-conductivity layer through electroplating. Both methods allow to reduce total power losses within the waveguide which are impacted by the conductivity of the metal. A set of mm-wave test vehicles was developed in WR-28 geometry (26.5 GHz to 40 GHz) being a straight and twisted transmission line section along with a narrowband filter to experimentally validate the approach. The models were 3D printed using Powder Bed Fusion out of stainless-steel powder, dry polished using glass microbeads, and then coated with copper. Up to 40% power loss reduction was obtained with respect to raw prints proving the performance of the approach.

Multilayer pantographic metamaterials, in short, pantographic blocks, have shown peculiar mechanical behavior, especially when their constitutive hinges are revolving (i.e., perfect) joints. The pantographic block, which is the subject of the present paper, has been printed using a Powder Bed Fusion technology and its hinges may be modeled as perfect ones. In the reported in situ 3-point flexural test, the predictions obtained by second gradient models for its mechanical response are shown to be experimentally consistent thanks to measurements via Digital Volume Correlation. The deformation applied by the upper central support is almost entirely shielded by the pantographic block, namely, the specimen barely crosses through the reference bottom plane defined by the lower lateral supports, even when subjected to very large deformations. The mathematical model employed herein captures this observation in terms of a nonlinear ‘arching’ effect activated in the beams of the pantographic structure, provided elastic locking is introduced to prevent pantographic zero-energy modes.

Laser Powder Bed Fusion (L-PBF) is a well-known Additive Manufacturing (AM) technology with a wide range of industrial applications. Potential occupational exposures to metal nanoparticles (NP) as by-products could occur in these processes, and no cogent occupational exposure limits are available. To contribute to this assessment, a monitoring campaign to measure the NP release pattern in two metal L-PBF facilities was carried out in two academic laboratories adopting L-PBF technology for research purposes. The monitored processes deal with two devices and three feedstock types, namely stainless steel (AISI 316L), aluminium-silicon alloy (A357) and pure copper, which are associated with different levels of industrial maturity. Prolonged environmental and personal real-time monitoring of NP concentration and size were performed, temperature and relative humidity were also measured during environmental monitoring. The measurements reveal a controlled NP release of the monitored processes, resulting in an average reduced exposure of the operators during the whole working shift, in compliance with proposed limit values (20 000 n cm-3 for density >6000 kg m-3 or 40 000 n cm-3 for density <6000 kg m-3). Nonetheless, the monitoring results show release events with an increase in NP concentration and a decrease in NP size corresponding with several actions usually performed during warm-up and cleaning, leading to exposures over 40-50 000 n cm-3 during a considerable time interval, especially during the manufacturing of pure copper powder. The results show that the actions of the operators, boundary conditions (relative humidity) and set-up of the L-PBF device have an impact on the amount of NP released and their size. Several release events (significant increase in NP concentration and decrease in NP size) are identified and associated with specific job tasks of the workers as well as building conditions. These results contribute to the definition of NP release benchmarks in AM processes and provide information to improve the operational conditions of L-PBF processes as well as safety guidelines for operators.

The present work aims at describing the workflow applied for the use of AM technologies during the worst phase of Covid-19 emergency. AM technologies have proved to be effective for the production in short time of many components to be used within ventilation systems, and which rapidly run out of stock due to unprecedent high demand. Moreover, many systems required modifications to prevent personnel’s infection. We report the workflow applied to face production needs, in terms of materials and technologies selection according to the specific requirements (disinfection, device criticality) and some practical examples.

Additive manufacturing (or three-dimensional (3D) printing) is constantly growing as an innovative process for the production of complex-shape components. Among the seven recognized 3D printing technologies, fused deposition modeling (FDM) covers a very important role, not only for producing representative 3D models, but, mainly due to the development of innovative material like Peek and Ultem, also for realizing structurally functional components. However, being FDM a production process involving high thermal gradients, non-negligible deformations and residual stresses may affect the 3D printed component. In this work we focus on meso/macroscopic simulations of the FDM process using abaqus software. After describing in detail the methodological process, we investigate the impact of several parameters and modeling choices (e.g., mesh size, material model, time-step size) on simulation outcomes and we validate the obtained results with experimental measurements.

Additive manufacturing (or 3D printing) is constantly growing as an innovative process for the production of complex-shape components. Among the seven recognized 3D printing technologies, powder bed fusion (PBF) covers a very important role for the production of structurally functional components starting from different metal powder. However, being PBF a production process involving very high thermal gradients, non-negligible deformations and residual stresses may affect the 3D printed component. One of the characterizing aspects of PBF is the evolution of the melt pool and the heat exchange with the surrounding solid powder. In literature many attempts to simulate melt pool evolution have been carried out, however the only approaches leading to interesting results rely on the lattice Boltzmann method. In this work, starting from the Boltzmann’s equation, we derive the lattice Boltzmann equation and we introduce the needed assumptions in order to recover the lattice Boltzmann method. Finally, we apply the lattice Boltzmann method to study some interesting problems related to powder bed fusion process, including droplets wetting, thermal convection and solid–liquid phase change.