Vacuum 3D printing of highly filled polymeric matrix composites

In this contribution, we have investigated how polymeric matrix composites for aerospace applications are affected, when fabricated at low pressure, by the additive manufacturing process. Commercial filaments have been selected based on their representativeness of materials derived from lunar resources. Standard samples of thermoplastic polymers reinforced by organic fibers and inorganic fillers have been printed inside a vacuum chamber, and their mechanical and thermal properties have been characterized and discussed based on the printing conditions. The reported study represents a preliminary investigation of the potential applicability of the 3D printing technology on highly filled polymers for extraterrestrial applications

Tailoring 3D printed cellulose acetate properties produced via direct ink writing: Densification through over-extrusion and evaporation rate control

In this study, we conducted a comprehensive experimental campaign aimed at controlling the final properties of 3D printed cellulose acetate. We equipped a commercial printer with a peristaltic pump to be able to print in a continuous fashion by means of the Direct Ink Writing technique. We investigated the effect of ink concentration and printing parameters on the density, mechanical and functional properties of printed objects. Furthermore, water absorption tests demonstrated the hygroscopic behavior of cellulose acetate, with higher water content in samples with lower densities. The diffusion of water within the polymer network followed Fickian diffusion, with the diffusion coefficient influenced by the density of samples. Overall, this study highlights the importance of printing conditions in achieving desired properties in 3D printed cellulose acetate. The ability to fine-tune the mechanical properties and water absorbance of 3D printed cellulose acetate makes it promising for applications in plant science and bioengineering. Highlights: Cellulose acetate has been 3D printed via Direct Ink Writing. The shear-thinning behavior allows for shape retention during printing. Density of printed samples is strongly controlled by printing parameters. Density of printed parts influences mechanical properties and water absorption

Design and testing of a 5-degrees-of-freedom, large working range micropositioning stage

This paper discloses the design principles of a compact 5-degrees of freedom piezoelectric micropositioning stage. The presented system exhibits the capability of generating large displacements, while maintaining a simple and modular structure. Due to a double-stage mechanical amplification strategy of the displacements generated by the piezoelectric actuators, the driving voltages can be kept low while reaching the desired performances in terms of amplitude of the working volume, thus allowing for the use of low-cost electronics. Experiments conducted to assess the static performances of a prototype device are in good agreement with the theoretical models. Possible applications include micromachining, micromanipulation and other positioning tasks in scientific instrumentation

A non-time based force control system for CNC applications

In this work, an innovative force control module is presented, which can be employed in CNC end milling machines in order to maintain a constant cutting force in the presence of parametric uncertainty for a time varying end milling process. The controller is a non-time based one; in fact, the desired tool position reference is delayed according to the integral of a proper function related to the on-line cutting force measurement. Such a controller, which is referred to as delayed reference control (DRC), consists in a outer force feedback loop around an inner position feedback loop. Two main advantages make this controller suitable for a commercial diffusion: it avoids complicate and time consuming algorithms for re-planning the path in response to cutting force and it does not require to design a new position feedback loop. Good experimental results are obtained by implementing the controller on a wood milling machine prototype. The system has shown a remarkable robustness in terms of immunity to the mechanical and electrical noise, working properly also with unfiltered control signals

\u201cFrattura delle frese in chirurgia orale\u201d

Obiettivo. Questo lavoro sperimentale nasce da una osservazione clinica. Lo scopo \ue8 quello di individuare eventuali fattori che possono contribuire a provocare la frattura delle frese pi\uf9 comunemente usate in chirurgia orale e quindi evitare eventuali rischi correlati a questa evenienza. Inoltre, si \ue8 voluto procedere anche alla caratterizzazione delle superfici di frattura al fine di ottenere dati su possibili difetti di fabbricazione o di stoccaggio, che possono alterare in qualche modo la struttura e quindi indebolirla. Metodi. Sono stati esaminati quattro gruppi di frese chirurgiche tipo Lindemann, nuove, per un totale di 40 frese. Il primo gruppo \ue8 stato preso come controllo, gli altri tre sono stati sottoposti rispettivamente a 5, 10 e 20 cicli di sterilizzazione, preceduti da un lavaggio con disinfettante. Le frese di ciascun gruppo sono state poi sottoposte alla prova meccanica a flessione a quattro punti per provocarne la rottura. Le superfici di frattura sono state poi studiate al SEM, comparandole alle frese rotte durante gli interventi chirurgici. Risultati. Le frese nuove non presentavano alcun difetto di lavorazione. Non \ue8 stato evidenziato alcun attacco corrosivo ad opera dei processi dei lavaggio e sterilizzazione. Conclusioni. Le prove meccaniche e micrografiche non hanno messo in evidenza differenze significative tra i diversi gruppi