Direct and Indirect Laser Sintering of Metals

Manufacturing functional prototypes and tools using conventional methods usually is a time consuming procedure with multiple steps. The pressure to get products to market faster has resulted in the creation of several Rapid Prototyping (RP) techniques. However, potentially one of the most important areas of Rapid Manufacturing (RM) technology lies in the field of Rapid Tooling (RT). Layer manufacture technologies are gaining increasing attention in the manufacturing sector for the production of polymer mould tooling. Layer manufacture techniques can be used in this potential manufacturing area to produce tooling either indirectly or directly, and powder metal based layer manufacture systems are considered an effective way of producing rapid tooling. Selective Laser Sintering (SLS) is one of available layer manufacture technologies. SLS is a sintering process in which shaped parts are built up layer by layer from bottom to top of powder material. A laser beam scans the powder layer, filling in the outline of each layers CAD-image, and heats the selected powder to fuse it. This work reports the results of an experimental study examining the potential of layer manufacturing processes to deliver production metal tooling for manufacture of polymer components. Characterisation of indirect selective laser sintering and direct selective laser sintering to provide the metal tooling is reported. Three main areas were addressed during the study: mechanical strength, accuracy, and build rate. Overviews of the results from the studies are presented. Two materials (RapidSteel 2.0 and special grade of highspeed steel) and also two generations of SLS machines Sinterstation 2000 and sinterstation research machine, which was constructed in Leeds) were used during this work

Biocorrosion behavior and cell viability of adhesive polymer coated magnesium based alloys for medical implants

The present study was ultimately aimed to design novel adhesive biodegradable polymer, poly(vinyl acetate) (PVAc), coatings onto Mg based alloys by the dip-coating technique in order to control the degradation rate and enhance the biocompatibility of magnesium alloys. The influence of various solvents on PVAc surface topography and their protection of Mg alloys were dramatically studied in vitro. Electrochemical polarization, degradation, and PVAc film cytocompatibility were also tested. Our results showed that the solvent had a significant effect on coating quality. PVAc/dichloromethane solution showed a porous structure and solution concentration could control the porous size. The coatings prepared using tetrahydrofuran and dimethylformamide solvents are exceptional in their ability to generate porous morphology even at low polymer concentration. In general, the corrosion performance appears to be different on different PVAc-solvent system. Immersion tests illustrated that the porous morphology on PVAc stabilized corrosion rates. A uniform corrosion attack in artificial simulation body fluid was also exhibited. The cytocompatibility of osteoblast cells (MC3T3) revealed high adherence, proliferation, and survival on the porous structure of PVAc coated Mg alloy, which was not observed for the uncoated samples. This novel PVAc coating is a promising candidate for biodegradable implant materials, which might widen the use of Mg based implants. Crown Copyright (C) 2012 Published by Elsevier B. V. All rights reserved

Enhanced biocorrosion resistance of surface modified magnesium alloys using inorganic/organic composite layer for biomedical applications

Magnesium (Mg) is a very active element with low surface stability. Thus, the biocorrosion resistance of Mg and its alloys in electrolytic physiological environments is extremely poor, which is the main limitation preventing their use in biomedical applications. In addition, generating an appropriate protective layer to coat the surface of such materials is a challenge due to the low level of surface stability. The aim of this study was to prepare thin Ti-O films on Mg substrates using electron beam physical vapor deposition (EB-PVD) in order to improve the surface stability of Mg. To provide further corrosion resistance and facilitate improved bioactivity and biocompatibility, Ti-O thin films were subsequently coated with PLA as a top layer by dip-coating. The surface properties of the coated layers were characterized by AFM, X-RD, FTIR, SEM, and EDS. Furthermore, the biocorrosion characteristics of samples were measured by electrochemical corrosion and hydrogen evaluation tests in standard simulation body fluid (SBF) at 37.5 degrees C. Our results showed that incorporation of a composite layer significantly reduced the rate of degradation of Mg alloys, particularly during the initial immersion stages. The rates of hydrogen evolution of Mg bars with and without a Ti-O/PLA composite coating after 18 days was approximately 4.86 and 13.4 ml cm(-2), respectively. Together, these results demonstrated that surface treatment of Mg substrates with Ti-O and PLA, together with the associated changes of surface reactivity and chemistry, provide a viable strategy to facilitate cell survival on otherwise non-biocompatible Mg surfaces. (C) 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved

Mechanical Properties and Wear Behavior of a Novel Composite of Acrylonitrile–Butadiene–Styrene Strengthened by Short Basalt Fiber

Polymer matrix composites (PMC) have a competitive and dominant role in a lot of industries, like aerospace and automobiles. Short basalt fiber (SBF) is used to strengthen acrylonitrile–butadiene–styrene (ABS) polymers as a composite. The composite material is fabricated using injection molding with a new technique to obtain a uniform distribution for the ABS matrix at an elevated temperature range from 140 °C to 240 °C. Four types of specimen were produced according to the mechanically mixed amounts of SBF, which were (5, 10, 15, 20) wt %. The produced material was tested for tension, hardness and impact to measure the enhancement of the mechanical properties of the ABS only and the ABS reinforced by SBF composite. Wear tests were carried out using a pin on disc at a velocity of 57.5 m/s at three normal loads of 5, 10 and 15 kN. Tensile strength increased with up to 5 wt % of SBF, then decreased with an increasing amount of SBF reinforcement, while surface hardness increased with increasing SBF. The impact strength was found to degrade with the whole increment of SBF. Wear resistance increased with the increasing SBF reinforcement amount at all applied normal loads

Engineering of electrically-conductive poly(ε-caprolactone)/ multi-walled carbon nanotubes composite nanofibers for tissue engineering applications

In this communication, air jet spinning (AJS)was used to successfully fabricate nanofibers of poly (ε-caprolactone)(PCL)onto which Multi-Walled Carbon Nanotubes (MWCNTs)were loaded at 0.5 to 1.0 wt % using a cost-effective fabrication technique. SEM images indicated that the incorporation of MWCNTs resulted in the production of larger fiber sizes with a more uniform size distribution than plain PCL. TEM observation showed the MWCNTs were parallel and oriented along the axes of the nanofibers. Specific interfacial interactions between the PCL and the MWCNTs enhanced the mechanical properties of the nanofibers in terms of tensile modulus and tensile strength. The electrical conductivity improved at the higher (1.0%)MWCNT concentration, alongside improved hydrophilicity, demonstrated through decreases in contact angle measurements. Moreover, in vitro studies with human bone osteosarcoma cells (Saos-2)revealed that MWCNT scaffolds displayed desired cell attachment and spreading. These high performance MWCNT-PCL nanocomposite fiber mats have been demonstrated as good candidates for modern microelectronics and tissue engineering applications

Enhancing mechanical and biodegradation properties of polyvinyl alcohol/silk fibroin nanofibers composite patches for cardiac tissue engineering

A biodegradable polyvinyl alcohol/silk fibroin (PVA/SF) nanofibrous heart patch with unique tensile properties was fabricated by an electrospinning technique based on a water-solvent system. The fabricated heart patches were exposed to 2% Glutaraldehyde vapor to provide a cross-linkage and tune the degradation behavior. Numerous characterizations of the modified PVA/SF patches such as surface morphology, chemical bonding, mechanical behavior, biodegradation, and biological assessment of the crosslinked PVA/SF patches were performed. It was found that pronounced and interconnected PVA/SF composite fibrous patches had an average nanofiber diameter of 228 ± 49 nm. In addition, incorporation of SF into PVA nanofibers enhanced the mechanical properties (i.e. tensile strength and tensile modulus) and tuning the degradation rate of the PVA/SF patch. Human cardiac fibroblast cells (HCFC) were cultured on the cross-linked composite patches and the results showed good cell proliferation and attachment on the patches bio-interface