Multifunctional HDPE/Cu biocidal nanocomposites for MEX additive manufactured parts: Perspectives for the defense industry

In this study, we investigated the performance improvement caused by the addition of copper(Cu)nanoparticles to high-density polyethylene(HDPE) matrix material. Composite materials, with filler percentages of 0.0, 2.0, 4.0, 6.0, 8.0, and 10.0 wt% were synthesized through the material extrusion(MEX)3D printing technique. The synthesized nanocomposite filaments were utilized for the manufacturing of specimens suitable for the experimental procedure that followed. Hence, we were able to systematically investigate their tensile, flexural, impact, and microhardness properties through various mechanical tests that were conducted according to the corresponding standards. Broadband Dielectric Spectroscopy was used to investigate the electrical/dielectric properties of the composites. Moreover, by employing means of Raman spectroscopy and thermogravimetric analysis(TGA) we were also able to further investigate their vibrational, structural, and thermal properties. Concomitantly, means of scanning electron microscopy(SEM), as well as atomic force microscopy(AFM), were used for the examination of the morphological and structural characteristics of the synthesized specimens, while energy-dispersive Xray spectroscopy(EDS) was also performed in order to receive a more detailed picture on the structural characteristics of the various synthesized composites. The corresponding nanomaterials were also assessed for their antibacterial properties regarding Staphylococcus aureus(S. aureus) and Escherichia coli(E. coli) with the assistance of a method named screening agar well diffusion. The results showed that the mechanical properties of HDPE benefited from the utilization of Cu as a filler, as they showed a notable improvement. The specimen of HDPE/Cu 4.0 wt% was the one that presented the highest levels of reinforcement in four out of the seven tested mechanical properties(for example, it exhibited a 36.7%improvement in the flexural strength, compared to the pure matrix). At the same time, the nanocomposites were efficient against the S. aureus bacterium and less efficient against the E. coli bacterium.The use of such multi-functional, robust nanocomposites in MEX 3D printing is positively impacting applications in various fields, most notably in the defense and security sectors. The latter becomes increasingly important if one takes into account that most firearms encompass various polymeric parts that require robustness and improved mechanical properties, while at the same time keeping the risk of spreading various infectious microorganisms at a bare minimum.

Extrusion-based additive manufacturing of Mg-Zn alloy scaffolds

Porous biodegradable Mg and its alloys are considered to have a great potential to serve as ideal bone substitutes.The recent progress in additive manufacturing(AM) has prompted its application to fabricate Mg scaffolds with geometrically ordered porous structures.Extrusionbased AM,followed by debinding and sintering,has been recently demonstrated as a powerful approach to fabricating such Mg scaffolds,which can avoid some crucial problems encountered when applying powder bed fusion AM techniques.However,such pure Mg scaffolds exhibit a too high rate of in vitro biodegradation.In the present research,alloying through a pre-alloyed Mg-Zn powder was ultilized to enhance the corrosion resistance and mechanical properties of AM geometrically ordered Mg-Zn scaffolds simultaneously.The in vitro biodegradation behavior,mechanical properties,and electrochemical response of the fabricated Mg-Zn scaffolds were evaluated.Moreover,the response of preosteoblasts to these scaffolds was systematically evaluated and compared with their response to pure Mg scaffolds.The Mg-Zn scaffolds with a porosity of 50.3% and strut density of 93.1% were composed of the Mg matrix and MgZn2second phase particles.The in vitro biodegradation rate of the Mg-Zn scaffolds decreased by 81% at day 1,as compared to pure Mg scaffolds.Over 28 days of static immersion in modified simulated body fluid,the corrosion rate of the Mg-Zn scaffolds decreased from 2.3± 0.9 mm/y to 0.7±0.1 mm/y.The yield strength and Young’s modulus of the Mg-Zn scaffolds were about 3 times as high as those of pure Mg scaffolds and remained within the range of those of trabecular bone throughout the biodegradation tests.Indirect culture of MC3T3-E1 preosteoblasts in Mg-Zn extracts indicated favorable cytocompatibility.In direct cell culture,some cells could spread and form filopodia on the surface of the Mg-Zn scaffolds.Overall,this study demonstrates the great potential of the extrusion-based AM Mg-Zn scaffolds to be further developed as biodegradable bone-substituting biomaterials.

Product Drawing Management System Based on Group Technology

With the development and widely used of the compute r technology, the CAD has been more and more used in the process of designing prod uct. The number of the engineering drawings will greatly increase because of the continually appearance of the new products. As a result, it has become a badly needed to be solved problem for us that how to rapidly and efficiently search an d appropriately preserve and manage the drawings. In this paper, a method of bui lding the product drawing management system for extrusion aluminum-type materia ls is discussed. This system is designed for the profile graphic of the aluminou s section material management by using Group Technology (GT) principle. Accordin g to the GT, we developed a classifying-coding system and drawing management sy stem about the extrusion aluminum-type materials through analyzing a large numb er of extrusion aluminum-type materials section drawings. The coding system has realized the flexible coding and hidden coding of the extrusion aluminum-type materials and then enhanced the flexibility and the expansible of the system. By supplying the designer with the human-computer interaction interface the drawi ng management system has been able to resolve many difficult problems such as se arch and manage the existed drawings about the extrusion aluminum-type material s very well. At the same time, it also helps the developing work enhance the abi lity of inheriting by applying this kind of variant method. In a word, with the help of this system we can not only shorten the designing time greatly and reduc e the cost of the product but also research the designing drawings rapidly. In o rder to output the data information related to the part drawing, the system uses the data-exchange standard to which the drawing support-software adapted as d ata-exchange interface. The system is advantageous to building a standard of dr awing design and increasing the efficiency of searching drawing and enhancing th e information management, which have had a base for building the best management system in the future. In addition, the paper has a detailed analysis about the principle of flexible classification code and data structure.

Characteristics of metal flow in cold extrusion under electric-hydraulic chattering

An experimental setup for cold extrusion process with electric-hydraulic chattering was developed and its working principle was introduced. The finite element （FE） model for a kind of cup part （material： 20Cr） was built by using the software Deform-3D. FE simulation experiments with and without electric-hydraulic chattering were carried out to analyze the velocity fields and the metal grid flow lines. The extrusion ex- periments of the cup part were also performed under different conditions. The difference of metal flow lines with and without electric-hydraulic chattering was discussed via a scanning electron microscope （SEM） and the Keyence super-depth three-dimensional microscopic system. The results showed that with the electric-hydraulic chattering, the velocity of material flow increases, whereas deformation resistance decreases. Electric hydraulic chattering results in easy metal flow, small bending degree of metal flow lines, slender and dense metal grains, and thereby an improved quality of the deformed parts.

Biochar filler in MEX and VPP additive manufacturing:characterization and reinforcement effects in polylactic acid and standard grade resin matrices

The development of sustainable and functional biocomposites remains a robust research and industrial claim.Herein,the efficiency of using eco-friendly biochar as reinforcement in Additive Manufacturing(AM)was investigated.Two AM technologies were applied,i.e.,vat photopolymerization(VPP)and material extrusion(MEX).A standard-grade resin in VPP and the also eco-friendly biodegradable Polylactic Acid(PLA)in the MEX process were selected as polymeric matrices.Biochar was prepared in the study from olive trees.Composites were developed for both 3D printing processes at different biochar loadings.Samples were 3D-printed and mechanically tested after international test standards.Thermogravimetric Analysis and Raman revealed the thermal and structural characteristics of the composites.Morphological and fractographic features were derived,among others,with Scanning Electron Microscopy(SEM)and Atomic Force Microscopy(AFM).Biochar was proven to be sufficient reinforcement agent,especially in the filament MEX process,reaching more than 20%improvement at 4 wt.%loading in tensile strength compared to the pure PLA control samples.In the VPP process,results were not as satisfactory,still,a 5%improvement was achieved in the flexural strength with 0.5 wt.%biochar loading.The findings prove the strong potential of biochar-based composites in AM applications,too.