The increase in accessibility of fused filament fabrication (FFF) machines has inspired the scientific community to work towards the understanding of the structural performance of components fabricated with this technology. Numerous attempts to characterize and to estimate the mechanical properties of structures fabricated with FFF have been reported in the literature. Experimental characterization of printed components has been reported extensively. However, few attempts have been made to predict properties of printed structures with computational models, and a lot less work with analytical approximations. As a result, a thorough review of reported experimental characterization and predictive models is presented with the aim of summarizing applicability and limitations of those approaches. Finally, recommendations on practices for characterizing printed materials are given and areas that deserve further research are proposed.
Hard roller burnishing is a cost-effective finishing and surface enhancement process where a ceramic ball rolls on the machined surface to flatten the roughness peaks. The ball is supported and lubricated by hydrostatic fluid in a special tool holder. The process not only improves surface finish but also imposes favorable compressive residual stresses in functional surfaces, which can lead to long fatigue life. Most research in the past focused on experimental studies. There is still a special need for a reliable finite element method (FEM) model that provides a fundamental understanding of the process mechanics. In this study, two-dimensional (2D) and three-dimensional FEM models for hard roller burnishing were established. The developed 2D FEM model was used to study the effects of process parameters (i.e., burnishing pressure, feed rate) on surface finish and residual stresses. The simulation results were evaluated and compared to the experimental data. Results show that the established FEM model could predict the residual stresses and provided useful information for the effect of process parameters. Both FEM and experiments show that burnishing pressure is the most influence, where high burnishing pressure produces less roughness and more compressive residual stress at the surface.
The circular economy (CE) model has become highly relevant in recent years, with the electronics industry being one of the sectors that has considered its application. Despite only a limited amount of literature being available on waste electric and electronic equipment (e-waste) in Mexico, the Mexican Government, academic institutions, and electronics industry have coordinated efforts to implement the CE in the country. This study evaluates the current technical and economic situation of cellphone e-waste generated in Mexico by surveying and analyzing the main actors that influence the management of this waste and using a material flow analysis. Extensive fieldwork was conducted in order to quantify the extent of cellphone e-waste processing in both formal and informal channels. The study of printed circuit boards in cellphones shows that the total value of cellphone e-waste materials ranges between $11.277 and $12.444 million USD per year in Mexico. However, a value of only $0.677 million USD is recycled through formal channels. After characterizing the remanufacturing and recycling CE loops, we conclude that the potential for improvement and advancing towards a CE model is significant
We used continuous flow micro-devices as bioreactors for the production of a glycosylated pharmaceutical product (a monoclonal antibody). We cultured CHO cells on the surface of PMMA/PDMS micro-channels that had been textured by micromachining and coated with fibronectin. Three different micro-channel geometries (a wavy channel, a zigzag channel, and a series of donut-shape reservoirs) were tested in a continuous flow regime in the range of 3 to 6 μL min(-1). Both the geometry of the micro-device and the flow rate had a significant effect on cell adhesion, cell proliferation, and monoclonal antibody production. The most efficient configuration was a series of donut-shaped reservoirs, which yielded mAb concentrations of 7.2 mg L(-1) at residence times lower than one minute and steady-state productivities above 9 mg mL(-1) min(-1). These rates are at about 3 orders of magnitude higher than those observed in suspended-cell stirred tank fed-batch bioreactors.
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