Conventional Manufacturing Techniques Research Articles

Processing of Materials for Regenerative Medicine Using Supercritical Fluid Technology.

The increase in the world demand of bone and cartilage replacement therapies urges the development of advanced synthetic scaffolds for regenerative purposes, not only providing mechanical support for tissue formation, but also promoting and guiding the tissue growth. Conventional manufacturing techniques have severe restrictions for designing these upgraded scaffolds, namely, regarding the use of organic solvents, shearing forces, and high operating temperatures. In this context, the use of supercritical fluid technology has emerged as an attractive solution to design solvent-free scaffolds and ingredients for scaffolds under mild processing conditions. The state-of-the-art on the technological endeavors for scaffold production using supercritical fluids is presented in this work with a critical review on the key processing parameters as well as the main advantages and limitations of each technique. A special stress is focused on the strategies suitable for the incorporation of bioactive agents (drugs, bioactive glasses, and growth factors) and the in vitro and in vivo performance of supercritical CO2-processed scaffolds.

Temperature measurement and theoretical analysis in high-speed grinding of hardened cold work die steel 9CrWMn

Cold work die steel 9CrWMn is one kind of high tensile strength steel which is used to manufacture stamping mold, shearing mold, roller die, cold heading, and cold extrusion die mold. Because of its high hardness and toughness, 9CrWMn is difficult to be machined by conventional manufacturing techniques. A series of high-speed grinding experiments were conducted for cold work die steel 9CrWMn using cBN wheel to assess the grinding characteristics in terms of grinding temperature. The grinding temperatures were measured by using a grindable thermocouple technique. 9CrWMn-constantan is not a kind of standard thermocouple, calibrating the thermocouple from the comparison method field of vision was done in this work. A series of temperature field simulations of high speed grinding of cold work die steel 9CrWMn with abrasive grains were conducted in Deform-3D and mesh adaptive technology was adopted to get optimized results. This paper gives theoretical analyses that contribute to the temperature phenomena. The simulation results were consistent with the experimental temperature measurements.

Curved fiber paths optimization of a composite cylindrical shell via Kriging-based approach

While conventional design and manufacturing techniques of fiber-reinforced laminates keep the fiber orientation angle constant within a layer, automated tow-placement technology allows fabricating laminates with curved fibers. This offers more flexibility to tailor the mechanical properties and improve the performance of laminated structures. Exploiting this flexibility requires an efficient method for finding optimal or near-optimal fiber configurations. In this paper, laminated cylindrical shells are studied. Curvilinear variations for the fiber orientations are adopted in the circumferential and longitudinal directions. The computational burden, typical in numerical optimization of complex structures, is reduced using a Kriging model, which substitutes for direct finite element simulation. A sequential quadratic programming algorithm is employed as local optimizer, coupled with a restart strategy to search for the global optimum in the entire design space. Some numerical cases are presented: the maximization of the fundamental frequency of the shell considering different boundary conditions and the minimization of the maximum displacement with a constraint on the buckling load.

Structural characterization of biomedical Co-Cr-Mo components produced by direct metal laser sintering.

Direct metal laser sintering (DMLS) is a technique to manufacture complex functional mechanical parts from a computer-aided design (CAD) model. Usually, the mechanical components produced by this procedure show higher residual porosity and poorer mechanical properties than those obtained by conventional manufacturing techniques. In this work, a Co-Cr-Mo alloy produced by DMLS with a composition suitable for biomedical applications was submitted to hardness measurements and structural characterization. The alloy showed a hardness value remarkably higher than those commonly obtained for the same cast or wrought alloys. In order to clarify the origin of this unexpected result, the sample microstructure was investigated by X-ray diffraction (XRD), electron microscopy (SEM and TEM) and energy dispersive microanalysis (EDX). For the first time, a homogeneous microstructure comprised of an intricate network of thin ε (hcp)-lamellae distributed inside a γ (fcc) phase was observed. The ε-lamellae grown on the {111}γ planes limit the dislocation slip inside the γ (fcc) phase, causing the measured hardness increase. The results suggest possible innovative applications of the DMLS technique to the production of mechanical parts in the medical and dental fields.

Influencia del volumen de fibras y curado posterior sobre el comportamiento post - fisura de un concreto de ultra alto desempeño

En el presente articulo se evalua el desempeno de un concreto de ultra alto desempeno reforzado con diferentes contenidos de fibras metalicas, el cual fue elaborado utilizando materiales accesibles en Colombia y con tecnicas de fabricacion convencional, es decir no se utilizaron presiones o temperaturas elevadas en la fabricacion de los diferentes especimenes. A este concreto de ultra alto desempeno se le realizaron pruebas de resistencia a la compresion uniaxial, resistencia a la flexion y de igual forma se evaluo el comportamiento de viguetas fisuradas a diferentes edades, las cuales fueron sometidas a diferentes tiempos de curado, con el fin de determinar la resistencia residual a flexion de las mismas. Se ha observado que el contenido en fibras y la adherencia que se genere entre las mismas y la matriz de concreto son aspectos de gran importancia, con el fin de garantizar que no haya perdida de la resistencia a la flexion, independientemente de la edad de fisuracion. Rev. ing. constr. [online]. 2014, vol.29, n.3, pp. 220-233. ISSN 0718-5073 http://dx.doi.org/10.4067/S0718-50732014000300001

Low-cost bandpass filter for terahertz applications

Compared to the visible and infrared regions of the electromagnetic spectrum, development of optical components in the terahertz region has progressed slowly even though the feature size of structures makes many of them easily attainable by many conventional manufacturing techniques. Of these, the performance of components with machined metal surfaces, such as filters, typically has suffered from the errors and inconsistencies in the manufacturing which has led many to manufacture these using more expensive deposition and processing tools. Here we show that by using a novel, high power Yb:doped pulsed nanosecond fiber laser system with exceptional beam quality, aluminum metal surfaces can be machined with high precision leading to a high quality band pass filter working in the terahertz frequency range. The filter was laser machined on a 0.05 mm thick aluminum substrate over a 1 cm $$^2$$ area where the unit cell in the pattern had an equilateral triangular geometry in which the base length between the holes and the diameters were machined with better than 4 % accuracy. The produced structures are modeled by utilizing the obtained structural parameters in a waveguide configuration and then characterized by the existing home-built time-domain terahertz spectrometers in our laboratories. The results show a near 100 % power transmission at the desired terahertz frequency range which suggests that these manufacturing techniques can be used to produce low-cost THz filters.

All-Inkjet-Printed Bottom-Gate Thin-Film Transistors Using UV Curable Dielectric for Well-Defined Source-Drain Electrodes

Technological restrictions of the inkjet printing technology for printed electronics can hinder its application potential, mainly due to the limited resolution and layer homogeneity in comparison to conventional manufacturing techniques for electronics. The manufacturing of active devices such as thin-film transistors with appropriate performance using printing technologies is still one of the current challenges towards industrial applications. This work demonstrates the application of an ultraviolet (UV) curable ink as insulating material for the gate dielectric. The advantage of the UV curable ink is its fast curing and the smooth surface enabling high resolution patterns on top of it. In this way, all-inkjet-printed organic thin-film transistors (OTFTs) were fabricated with silver electrodes, UV curable gate dielectric, and 6,13-bis(triisopropylsilylethynyl)pentacene for the active semiconductor layer. By fine tuning of processing parameters and pattern geometries, a stable channel length of about 10 μm was obtained in the bottom-gate configuration without the need of additional steps, suggesting a way to build low-cost all-inkjet-printed OTFTs with well-defined source-drain electrodes and fast UV curable dielectric without any additional steps. The inkjet-printed device is characterized by an electron mobility of 0.012 cm2 V−1 s−1 and on/off ratio of 103.

Plasmonic hollow-core photonic band gap fiber for efficient sensing of biofluids

We report a new family of hollow-core photonic crystal fibers with embedded metal wires for sensitive refractive index measurement of fluids. These fibers operate on the principle of resonant coupling of the guided core mode with the surface plasmon mode generated at the surface of metal wires embedded in the photonic crystal structure. A maximum sensitivity of 2151 nm RIU−1 (nanometer per refractive index unit) can be achieved even for refractive index values lower than 1.26. The fiber is simple in design and can be fabricated with a certain modification to the conventional hollow-core photonic band gap fiber manufacturing technique. The proposed design is useful for detecting a small change in refractive index of the sample and may be implemented to estimate the bulk permittivity of the core fluid.

Few mode Er^3+-doped fiber with micro-structured core for mode division multiplexing in the C-band

Design and experimental characterization of Er(3+)-doped fiber amplifiers supporting 6 spatial modes in wavelength division multiplexing regime are reported. The study is first focused on Er(3+)-doped circular ring-structured profiles accessible with conventional fiber manufacturing techniques. However, these fiber designs, optimized for gain equalization, prove to be difficult to obtain experimentally. So as to go beyond these limits, an alternative approach based on a "pixelated" Er(3+)-doped core is proposed. Several possible designs are theoretically investigated and a first fabrication of micro-structured fiber is presented.

Mouth Dissolving Tablets – A Review

Conventional dosage form such as tablets and capsules are the most popular among all dosage forms existing today because of its convenience of self administration, compactness and easy manufacturing. However these dosage forms are facing problems like hand tremors, dysphasia in case of geriatric patients, the underdeveloped muscular and nervous systems in young individuals and in case of uncooperative patients, the problem of swallowing is common phenomenon which leads to poor patient compliance. To overcome these problems, mouth dissolving tablets have been developed, which having good hardness, dose uniformity, easy administration and serves as the first choice of dosage form for pediatrics, geriatrics and travelling patients. This report summarizes the details of ingredients used in preparation of mouth dissolving tablets; conventional manufacturing techniques for mouth dissolving tablets; patented technologies for preparation of mouth dissolving tablets; evaluation of mouth dissolving tablet; and mechanism of action of mouth dissolving tablets.

Auxetic oesophageal stents: structure and mechanical properties

Oesophageal cancer is the ninth leading cause of malignant cancer death and its prognosis remains poor, ranking as the sixth most frequent cause of death in the world. This research work aims to adopt an Auxetic (rotating-squares) geometry device, that had previously been examined theoretically and analysed by Grima and Evans (J Mater Sci Lett 19(17):1563-1565, 2000), to produce a novel Auxetic oesophageal stent and stent-grafts relevant to the palliative treatment of oesophageal cancer and also for the prevention of dysphagia. This paper discusses the manufacture of a small diameter Auxetic oesophageal stent and stent-graft. The oral deployment of such an Auxetic stent would be simplest if a commercial balloon dilatational catheter was used as this obviates the need for an expensive dedicated delivery system. A novel manufacturing route was employed in this research to develop both Auxetic films and Auxetic oesophageal stents, which ranged from conventional subtractive techniques to a new additive manufacturing method. Polyurethane was selected as a material for the fabrication of Auxetic films and Auxetic oesophageal stents because of its good biocompatibility and non-toxicological properties. The Auxetic films were later used for the fabrication of seamed Auxetic oesophageal stents. The flexible polyurethane tubular grafts were also attached to the inner luminal side of the seamless Auxetic oesophageal stents, in order to prevent tumour in-growth. Scanning electron microscopy was used to conduct surface morphology study by using different Auxetic specimens developed from different conventional and new additive manufacturing techniques. Tensile testing of the Auxetic films was performed to characterise their mechanical properties. The stent expansion tests of the Auxetic stents were done to analyse the longitudinal extension and radial expansion of the Auxetic stent at a range of radial pressures applied by the balloon catheter, and to also identify the pressure values where the Auxetic stent fails. Finite element models of both Auxetic film and Auxetic stent were developed, and the results were compared with experimental results with a good agreement. The tensile testing of the Auxetic polyurethane films revealed that the Poisson's ratio of the sample ranged between -0.87 and -0.963 at different uniaxial tensile load values. From the stent expansion test, it was found that the Auxetic oesophageal stent radially expanded from 0.5 to 5.73mm and longitudinally extended from 0.15 to 1.83mm at a range of applied pressure increments (0.5-2.7bar) from the balloon catheter.

3D printing for CO2 capture and chemical engineering design

Three-dimensional printing is a form of additive manufacturing that allows the fabrication of items directly from digital files, allowing the user to virtually produce any solid object on demand. Three-dimensional printing is already a frequently discussed topic in the mainstream media and is beginning to find a number of applications in research laboratories. The authors have recognized that 3D printing can have many roles in the design of chemical engineering processes as a means of fabricating parts or perhaps entire unit operations. The authors foresee many opportunities for 3D printing as a means of producing novel and advanced components and entire devices for gas treating. Gas treating (i.e. the removal of one or more contaminants from a gaseous mixture) plays a crucial role in many existing and emerging energy-related processes including natural gas sweetening, flue gas desulfurization and pre- and post-combustion carbon dioxide capture. These processes are typically carried out in absorption columns containing trays or packing that provide interfaces for gas–liquid contacting. New devices such as membrane contactors are also emerging as alternative mechanisms for achieving separation of gases with potential cost and energy-saving benefits derived from having smaller footprints, being of lighter weight and having much larger interfacial areas. Yet in all cases, the design, cost and ability to optimize gas–liquid contactors may be limited by conventional manufacturing techniques. In this respect, 3D printing could be a mechanism by which to achieve improvements on existing technologies and more rapidly deploy novel devices. Here, the authors describe their efforts to date in the application of 3D printing for the fabrication of components and devices for carbon dioxide–capture applications and provide perspective on design strategies, opportunities and challenges.

A comparison of 3D poly(ε-caprolactone) tissue engineering scaffolds produced with conventional and additive manufacturing techniques by means of quantitative analysis of SR μ-CT images

The technique used to produce a 3D tissue engineering (TE) scaffold is of fundamental importance in order to guarantee its proper morphological characteristics. An accurate assessment of the resulting structural properties is therefore crucial in order to evaluate the effectiveness of the produced scaffold. Synchrotron radiation (SR) computed microtomography (μ-CT) combined with further image analysis seems to be one of the most effective techniques to this aim. However, a quantitative assessment of the morphological parameters directly from the reconstructed images is a non trivial task. This study considers two different poly(ε-caprolactone) (PCL) scaffolds fabricated with a conventional technique (Solvent Casting Particulate Leaching, SCPL) and an additive manufacturing (AM) technique (BioCell Printing), respectively. With the first technique it is possible to produce scaffolds with random, non-regular, rounded pore geometry. The AM technique instead is able to produce scaffolds with square-shaped interconnected pores of regular dimension. Therefore, the final morphology of the AM scaffolds can be predicted and the resulting model can be used for the validation of the applied imaging and image analysis protocols. It is here reported a SR μ-CT image analysis approach that is able to effectively and accurately reveal the differences in the pore- and throat-size distributions as well as connectivity of both AM and SCPL scaffolds.

Inverse Jet Electrochemical Machining for Functional Edge Shaping of Micro Bores

Micro bores are used for several high-precision applications, especially in hydraulic systems and fuel injectors. In this case the shape, particularly the edge rounding of the injection spray hole, has a significant influence on the atomization of fluids and therefore also on the combustion process [1]. From the present knowledge about the relationship between bore geometry and hydraulic properties requirements were derived which are not feasible applying conventional manufacturing techniques. In particular, it is currently not possible to adjust the flow coefficient and the cavitation point independent of each other. The flow coefficient significantly influences the atomization, while the cavitation is necessary to prevent coking of the injection holes. One way to decouple the flow coefficient and cavitation behavior is a functional edge rounding of the borehole. This cannot be represented by the previous ly applied hydroerosive rounding. Therefore inverse Jet Electrochemical Machining (inverse Jet -ECM) opens up new possibilities, as the erosion area is localised by the jet. In Jet -ECM the electrolyte is supplied through a nozzle at an average speed of about 20 m/s and adjusted perpendicular to the work piece surface. Forming a free jet leads to a high localization of the current density resulting in a much localized machining area direct below the nozzle [2]. In this study an edge rounding of the micro nozzle bore is realized by an inversion of the Jet-ECM principle.

Nano carbon containing MgO-C refractory: Effect of graphite content

Development of low carbon containing MgO-C refractories has been studied containing a fixed 0.9wt% of nano carbon and 1–9wt% of flake graphite. Refractory compositions were prepared and processed as per the conventional manufacturing techniques of MgO-C refractory. Properties of the different compositions were evaluated and also compared against the conventional MgO-C refractory containing 10wt% graphite prepared under exactly similar conditions. Addition of 3wt% of flake graphite in combination with 0.9wt% of nano carbon black was found to be optimum and resulted in better/comparable properties to that of conventional MgO-C refractory.

The Modeling and Simulation of Mirostrip Bandpass Filter Using ADS

Microstrip filter is used widely in wireless communication area, especially in WLAN. Compared to the conventional manufacturing techniques using lumped element, we can get extremely better characters in high frequency wave band using microstrip lines. ADS2008 (Agilent Advanced Design System 2008) is an excellent software platform for high frequency and high speed EDA manufacturing. In this letter, the modeling of microstrip filter which works at appointed frequency is got by transforming the lumped elements to microstrip elements. Finally, the microstrip filter simulated, optimized by ADS2008.

Study on low carbon containing MgO-C refractory: Use of nano carbon

Development of nano carbon containing magnesia carbon refractories has been studied to reduce the total carbon content, thereby reducing the heat loss from the metallurgical process and producing more eco-friendly refractories. The carbon contamination from refractory to liquid metal will be minimized using low amount of nano carbon. Different percentages of nano carbon are used in combination with graphite as carbon source and the total carbon is maintained below the half of the total carbon of the conventional MgO-C refractories. The compositions were processed as per the conventional manufacturing techniques and the properties were evaluated and compared against the conventional refractory prepared under exactly similar conditions. Also elemental mapping of carbon was done to study the distribution of the nano carbon in the matrix.

Manufacture of Aluminum Nanocomposites: <i>A Critical Review</i>

In the last two decades, metal matrix nanocomposites have witnessed tremendous growth. Particulate-reinforced nanocomposites have been extensively employed in the automotive industry for their capability to withstand high temperature and pressure conditions. Several manufacturing approaches have been used to fabricate them. Non-homogeneous particle dispersion and poor interface bonding are the main drawbacks of conventional manufacturing techniques. A critical review of nanocomposite manufacturing processes is presented; the distinction between ex-situ and in-situ processes is discussed in some detail. Moreover, in-situ gas/liquid processes are elaborated and their advantages are discussed. The thermodynamics and kinetics of the reaction between the precursor gas and the liquid metal have been analyzed and their role on particle formation studied. This critical review will provide the reader with an overview of nanocomposite manufacturing methods along with a clear understanding of advantages and disadvantages.

3D Elastomeric Scaffolds Fabricated by Casting in Micro End Milled Moulds

It is known that conventional scaffold manufacturing techniques have low reproducibility and control of the micro-architecture features. Although there have been advances in bone tissue engineering fabrication, there is no consensus on the optimized parameter designs or clear understanding of the microfluidic interactions required for tissue regeneration. In this work, we introduce a new inexpensive fabrication method of producing pore designs of 3D-elastomeric structures with high controlled geometry of orthogonal arrays. The present fabrication method utilizes a permanent and reusable micro-machined mould along with a micro-casted process to efficiently fabricate diverse 3D feature directly. This fabrication method, without multiple process steps, would be suitable to support experiments of controlled environment for flow effects in 3D bone scaffolds.

Micromachined Ultrasonic Print-Head for Deposition of High-Viscosity Materials

The recent application of inkjet printing to fabrication of three-dimensional, multilayer and multimaterial parts has tested the limits of conventional printing-based additive manufacturing techniques. The novel method presented here, termed as additive manufacturing via microarray deposition (AMMD), expands the allowable range of physical properties of printed fluids to include important, high-viscosity production materials (e.g., polyurethane resins). AMMD relies on a piezoelectrically driven ultrasonic print-head that generates continuous streams of droplets from 45 μm orifices while operating in the 0.5–3.0 MHz frequency range. The device is composed of a bulk ceramic piezoelectric transducer for ultrasound generation, a reservoir for the material to be printed, and a silicon micromachined array of liquid horn structures, which make up the ejection nozzles. Unique to this new printing technique are the high frequency of operation, use of fluid cavity resonances to assist ejection, and acoustic wave focusing to generate the pressure gradient required to form and eject droplets. We present the initial characterization of a micromachined print-head for deposition of fluids that cannot be used with conventional printing-based rapid prototyping techniques. Glycerol-water mixtures with a range of properties (surface tensions of ∼58–73 mN/m and viscosities of 0.7–380 mN s/m2) were used as representative printing fluids for most investigations. Sustained ejection was observed in all cases. In addition, successful ejection of a urethane-based photopolymer resin (surface tension of ∼25–30 mN/m and viscosity of 900–3000 mN s/m2) was achieved in short duration bursts. Peaks in the ejection quality were found to correspond to predicted device resonances. Based on these results, we have demonstrated the printing of fluids that fall well outside of the accepted range for the previously introduced printing indicator. The micromachined ultrasonic print-head achieves sustained printing of fluids up to 380 mN s/m2, far above the typical printable range.