RESUMO
This investigation analyzes the main contributions that additive manufacturing (AM) technology provides to the world in fighting against the pandemic COVID-19 from a materials and applications perspective. With this aim, different sources, which include academic reports, initiatives, and industrial companies, have been systematically analyzed. The AM technology applications include protective masks, mechanical ventilator parts, social distancing signage, and parts for detection and disinfection equipment (Ju, 2020). There is a substantially increased number of contributions from AM technology to this global issue, which is expected to continuously increase until a sound solution is found. The materials and manufacturing technologies in addition to the current challenges and opportunities were analyzed as well. These contributions came from a lot of countries, which can be used as a future model to work in massive collaboration, technology networking, and adaptability, all lined up to provide potential solutions for some of the biggest challenges the human society might face in the future.
RESUMO
In this study, a novel finishing method, entitled clustered magnetorheological finish (CMRF), was proposed to improve surface finish of the silicon nitride ( Si 3 N 4 ) balls with ultra fine precision. The effects of different polishing parameters including rotation speeds, eccentricities and the machining gaps on surface finish of Si 3 N 4 balls were investigated by analyzing the roughness, sphericity and the micro morphology of the machined surface. The experimental results showed that the polishing parameters significantly influenced the surface finish. The best surface finish was obtained by using the polishing parameters: the machining gap of 0.8 mm, the eccentricity of 10 mm and the rotation ratio of 3/4. To further investigate the influence of the polishing parameters on the surface finish, an analytical model was also developed to analyze the kinematics of the ceramic ball during CMRF process. The resulting surface finish, as a function of different polishing parameters employed, was evaluated by analyzing the visualized finishing trace and the distribution of the contact points. The simulative results showed that the distribution and trace of the contact points changed with different polishing parameters, which was in accordance with the results of experiments.
RESUMO
The structural and/or functional design of multiphase ceramics, along with their processing, are timely research topics in the area of field-assisted sintering techniques, such as spark plasma sintering, especially for systems containing both electrically insulating and conductive phases. In the present study, spark plasma sintering of Si3N4-TiN composites was investigated by changing the TiN particle size and electrical current waveform. Their combined effects on both the densification behavior and α-to-ß phase conversion of the Si3N4 matrix was studied and compared by means of a thermodynamic approach and dilatometric measurements. Through the control of TiN phase characteristics and heating mode, double-layered Si3N4-based components were also prepared using a one-step spark plasma sintering process, which was compared with conventional hot-pressing. It was shown that the size of the conductive TiN phase has a significant influence on the particle rearrangement, with the formation of a liquid phase, and the solution-diffusion-precipitation process, through the field-induced local heating and electrowetting mechanisms. Moreover, the contribution of current pulsing to the densification and α-to-ß conversion of the layered Si3N4-based components was mostly dependent upon the particle size distribution and content of the TiN phase, indicating that the electric-field effect is dependent upon current path.