Manufacturing by combining Selective Laser Melting and Selective Laser Erosion/laser re-melting

This study presents an experimental investigation to improve Selective Laser Melting (SLM) regarding aspects such as surface roughness, density, precision and micro machining capability by employing secondary processes such as Selective Laser Erosion (SLE) and laser re-melting. SLM is a layered additive manufacturing technique for the direct fabrication of functional parts by fusing together metal powder particles. Laser re-melting, applied after each layer or only on the top surfaces, is used to improve the roughness and density while SLE, a subtractive process, is combined with SLM to improve the precision and micro machining capability.     

艾哈迈德·阿德南·萨伊贡艺术中心,伊兹密尔,土耳其

<正>一座建筑的性能应当如何来衡量?除了通过统治当代建筑舆论的美学、技术以及经济价值来进行描述之外,我们还能够如何来阐释一座建筑,尤其是一座致力于庇护那些渴望展现自己的艺术家的建筑?有人会问成功的表演是如何实现的,表演者是如何进行伪装的、又是如何展现自己的?根据海德格尔的理论,当我们看不到钉子的时候,铁锤的表现才是成功的;钉子本身的出现通常表明出现了问题。     

Investigation of laser and process parameters for Selective Laser Erosion

The process of Selective Laser Erosion (SLE) was investigated to study the effects of different process and laser parameters on the process outputs such as surface quality and erosion rate. The SLE process is a direct method to remove material in a layer-by-layer fashion due to high energy densities provided by the laser beam. In addition to its direct use as a subtractive manufacturing method, SLE may be used in combination with layer-additive techniques such as Selective Laser Melting (SLM). Such combination mainly makes sense when both processes can be performed with the same laser. However, one of the major problems involved in SLE process is the high number of the laser and process parameters (laser power, pulse frequency, scan speed, scan spacing, ambient atmosphere, etc.) and the complexity of the relations between them which has not yet been investigated completely.This paper presents an overview of the laser erosion process with nano-second Nd:YAG laser pulses and the results of several single-factor experiments that were carried out to determine the influence of the major parameters on the depth of erosion per layer and surface roughness. Additionally, the relations between the parameters are studied to investigate the interactions between them. The results from single-factor experiments showed that some relations were highly governed by the power intensity of the laser beam and also that cross interactions between the parameters play an important role on the output characteristics. The paper explains how multiple parameters (spot size, pulse frequency, scan speed, scan spacing) can be combined to define two indirectly controlled geometrical parameters, namely the scan and pulse overlap factors. Those two parameters allow calculating the number of hits of the laser beam on a same location on the workpiece possible which is the first step in physical modeling the topography of the surface left behind.     

Fractional In Situ Pad Conditioning in Chemical Mechanical Planarization

Material removal rate, shear force and variance of shear force during copper polishing are studied as a function of pad conditioning scheme: 0% in situ conditioning (i.e., basically the equivalent of ex situ conditioning) and fractional in situ conditioning variants (i.e., conditioning during the first 25, 50, 75 or 100% of the total polish time). Spectral analysis of raw shear force data is employed to help elucidate the fundamental physical phenomena during copper chemical mechanical planarization. Fast Fourier transform is performed to convert the shear force data from time domain into frequency domain. The energy distribution of copper polishing is quantified which sheds light on the effect of fractional in situ pad conditioning. Variance of shear force and spectral analysis indicate that pad micro-texture evolution ceases after 50% fractional conditioning, thereby indicating that in situ conditioning time can be reduced during a given polishing process thus extending pad life. This study shows that a combination of unique spectral fingerprinting and analysis of force variance can be used to monitor the effect of pad conditioning in real time. This work also underscores the importance of real-time detection and non-destructive method to extend pad life and consumable usage during CMP by optimizing the pad conditioning time.     

Thermal effects of two immiscible fluids through a permeable stenosed artery having nanofluid in the core region

A theoretical investigation of two-layered fluid flow in a stenosed tube having permeable walls is studied. The fluid (blood with nanoparticles) within the core region behaves as a non-Newtonian fluid (nanofluid) and the fluid within the peripheral layer behaves as a Newtonian fluid. Flow equations are linearized considering mild stenoses. The closed form mathematical expressions for flow resistance and wall shear stress are computed. The problem is solved using HPM (homotopy perturbation method). The numerical calculations of flow parameters (like flow resistance, wall shear stress) are performed and are discussed graphically. A novel result is found that with increased permeability and viscosity, the resistance of the fluid flow and shear at the wall is found to decrease. Moreover, the velocity profiles are increasing in the radial direction with the enhancement of viscosity of the fluid in the peripheral layer but decrease with permeability. Streamlines are drawn to examine the flow pattern.     

Can we restore the colour of long-term discoloured resin composites by noninvasive methods?

The aim of this study is to investigate the effect of toothbrushing and paste repolishing on the colour restitution of long-term coffee discoloured prefabricated and direct resin composites. One prefabricated (Componeer-Coltène) and three direct resin composites (Brilliant Ever Glow-Coltène, Essentia-GC, Harmonize-Kerr) were tested. Componeer samples were prepared with and without polishing while the other groups were all polished. After baseline colour-measurement, the specimens were immersed in coffee for 3-month and colour-measurement was repeated, then a simulation of 1-year of toothbrushing (Toothbrush Simulation ZM-3.4-SD Mechatronics) with Pro-Expert Professional Protection-Ipana, 3D White Luxe Perfection-Ipana, and White Ruscello-GC toothpaste was performed. Colour-changes (ΔE) after toothbrushing and repolishing with polishing paste (Enamelize, Cosmodent) were calculated. The discolouration occurred after prolonged exposure to a coffee solution was above the clinically acceptable level of ΔE = 2 in all groups, except Componeer polished group. The lowest discoloured group was Componeer polished (ΔE = 1.66 ± 0.32) while the highest was Essentia group (ΔE = 4.30 ± 0.48). The samples toothbrushed with White Ruscello exhibited the greatest colour restitution (ΔE = 2.06 ± 0.75) (P < .05). After paste repolishing, slight colour restitution was observed among all the groups, but the differences between them remained the same as after the toothbrushing procedure. Prolonged exposure to coffee solution affects the colour of the resin composites and noninvasive methods can provide colour restitution below the critical value for visual perception (ΔE = 3.3). Noninvasive procedures such as toothbrushing with a whitening toothpaste or repolishing with a polishing paste may ensure the colour restitution of direct resin composite restorations until a clinically acceptable level.     

Pattern evolution in shallow trench isolation chemical mechanical planarization via real-time shear and down forces spectral analyses

This study explores the transition of force spectral fingerprints of shallow trench isolation chemical mechanical planarization during early evolution of wafer topography and layer transition from silicon dioxide to silicon nitride. Polishing was done on a polisher and tribometer capable of measuring shear force and down force in real-time. Fast Fourier Transformation is performed to convert the force data from time domain to frequency domain and to illustrate the spectral amplitude distribution of the force. Such frequency spectra provide in-depth insights into the interactions among abrasive particles, pad and wafer. Shallow trench isolation patterned wafers are over-polished using cerium oxide slurry. Results show that shear force increases during polishing when the silicon dioxide layer is removed thus exposing the silicon nitride layer. Unique and consistent spectral fingerprints are generated showing significant changes in several fundamental peaks during the early evolution of wafer topography and subsequent layer transition to silicon nitride polishing. Variance of force is also plotted to show the progression of pattern evolution. Results show that a combination of unique spectral fingerprinting, coefficient of friction as well as analyses of force and its variance (based on shear and down force) can be used as to monitor in real-time the polishing progress during shallow trench isolation chemical mechanical planarization.     

Preliminary characterisation of cornelian cherry (Cornusmas L.) genotypes for their physico-chemical properties

Fruit weight, antioxidant capacity, total anthocyanins, total phenolics, ascorbic acid, soluble solid content (SSC), reducing sugar and acidity of a number of selected cornelian cherry (Cornusmas L.) genotypes of varied pigmentation were investigated. Two methods, namely β-carotene bleaching and ferric reducing antioxidant power (FRAP) were used to determine total antioxidant capacity, while Folin–Ciocalteu reagent was used to determine total phenols. Fruit weight, SSC and ascorbic acid content of genotypes were 2.09–9.17; 12.53–21.17% and 29–112 mg/100 g, respectively. Antioxidant activity and total phenolic content varied among genotypes and 44-18 genotype had the highest antioxidant capacity using both methods. This genotype also had the highest total phenolic (74.8 mg GAE/g DW) and total anthocyanin (115 mg cyanidin-3-glucoside equivalents /100 g FW) content. There are linear relationships between antioxidant capacities and total phenols. The present study demonstrates the potential of certain cornelian cherry genotypes, notably 44-18, for improvement of nutritional value through germplasm enhancement programmes.     

3D‐Printed Microrobotic Transporters with Recapitulated Stem Cell Niche for Programmable and Active Cell Delivery

Poor retention rate, low targeting accuracy, and spontaneous transformation of stem cells present major clinical barriers to the success of therapies based on stem cell transplantation. To improve the clinical outcome, efforts should focus on the active delivery of stem cells to the target tissue site within a controlled environment, increasing survival, and fate for effective tissue regeneration. Here, a remotely steerable microrobotic cell transporter is presented with a biophysically and biochemically recapitulated stem cell niche for directing stem cells towards a pre‐destined cell lineage. The magnetically actuated double‐helical cell microtransporters of 76 µm length and 20 µm inner cavity diameter are 3D printed where biological and mechanical information regarding the stem cell niche are encoded at the single‐cell level. Cell‐loaded microtransporters are mobilized inside confined microchannels along computer‐controlled trajectories under rotating magnetic fields. The mesenchymal stem cells are shown retaining their differentiation capacities to commit to the osteogenic lineage when stimulated inside the microswimmers in vitro. Such a microrobotic approach has the potential to enable the development of active microcarriers with embedded functionalities for controlled and precisely localized therapeutic cell delivery.     

Selenophene-bearing low-band-gap conjugated polymers: tuning optoelectronic properties via fluorene and carbazole as donor moieties

Polymer Bulletin - In this study, two donor–acceptor (D–A)-type conjugated polymers, namely PQSeCz and PQSeFl, were designed and synthesized. Selenophene was incorporated as the...