Potential of cold gas dynamic spray as additive manufacturing technology

In this paper, the application of cold spray (CS) coating deposition technology as additive manufacturing technique is discussed. Absence of material melting during CS deposition permits to obtain deposits with low value of residual stresses and to preserve the phase composition of source material which is a very important advantage. In this paper, the latest developments in the field of cold spray such as micronozzle device and new multimaterial deposition approach permitting to significantly enlarge the potential of cold spray as additive manufacturing technology is discussed.     

Thermal effect of high-velocity particle impingements on coating quality in cold gas dynamic spray operations

Journal of Mechanical Science and Technology - This investigation is aimed to evaluate thermal effects of the high-velocity particle impingement on the coating quality in CGDS (cold gas dynamic...     

On the process capability of the solid free-form fabrication: a case study of scaffold moulds for tissue engineering

This study applies the methodology and procedure of process capability to investigate a solid free-form fabrication technique as a manufacturing method to produce scaffold moulds for tissue engineering. The process capability Cpk and process performance Ppk of scaffold mould manufacture using a solid free-form fabrication technique has been analysed with respect to the dimension deviations. A solid free-form fabrication machine T66 was used to fabricate scaffold moulds in this study and is able to create features that ranged from 200 microm to 1000 microm. The analysis showed that the printing process under the normal cooling conditions of the printing chamber was in statistical control but gave low process capability indices, indicating that the process was 'inadequate' for production of 'dimension-consistent' scaffold moulds. The study demonstrates that, by lowering the temperature of the cooling conditions, the capability Cpk of the printing process can be improved (about threefold) sufficiently to ensure the consistent production of scaffold moulds with dimension characteristics within their specification limits.     

旋转式微发电机的设计与制造

为了实现旋转式微发电机对微系统的持续供电,研究了旋转式微发电机的设计、制造以及实验方法.首先,设计了具有单转子和单定子的三相、永磁同步微发电机模型.使用传统的磁路分析法得出了微发电机气隙磁密和感应电动势的表达式,确定了微发电机的主要设计参数.对模型进行有限元分析,得到了感应电动势波形.然后,利用精密加工技术加工了转子和...     

A feasibility study of microscale fabrication by ultrasonic-shoe centerless grinding

The present authors proposed a new centerless grinding technique, namely ultrasonic-shoe centerless grinding, which they validated experimentally in a previous study [Wu Y, Fan Y, Kato M, Wang J, Syoji K, Kuriyagawa T. A new centerless grinding technique without employing a regulating wheel. Key Eng Mater 2003;238–239:355–60]. Rather than a regulating wheel as in conventional centerless grinding, the new method uses a plate-shaped ultrasonic shoe, on the end face of which micro elliptic motion is generated, to support the workpiece and control its rotational motion. This enables the fabrication of a microscale cylindrical component less than 100 μm in diameter with an extremely large aspect ratio, which is extremely difficult to produce by conventional machining techniques. In the present study, in order to develop a novel technique for the fabrication of microscale cylindrical components, first an apparatus capable of microscale fabrication was designed and constructed based on the ultrasonic-shoe centerless grinding method. Following initial performance tests, the apparatus was tested by conducting a grinding run on a tungsten carbide test-piece, 0.6 mm in diameter and 15 mm in length. The result was a microscale cylindrical component, around 60 μm in diameter and 15 mm in length, with an aspect ratio of over 250, which validated the new technique proposed for microscale fabrication.     

Experimental study on spray etching process in micro fabrication of lead frame

The objective of this study is to obtain detailed information for the micro fabrication of lead frames by applying spray technology to wet etching process. Wet etching experiments were performed with different etching parameters such as injection pressure, distance from nozzle tip to etched substrate, nozzle pitch and etchant temperature. The characteristics of single and twin spray were measured to investigate the correlation between the spray characteristics and the etching characteristics. Drop size and velocity were measured by Phase-Doppler Anemometer (PDA). Four liquids of different viscosity were used to reveal the effects of viscosity on the spray characteristics. The results indicated that the shorter the distance from nozzle tip and the nozzle pitch, the larger etching factor became. The average etching factor had good positive correlation with average axial velocity and impact force. It was found that the etching characteristics depended strongly on the spray characteristics.     

Surface roughness and geometrical characterization of ultra-thick micro moulds for ceramic micro fabrication using soft lithography

Ceramic micro fabrication using soft lithography is a well-known technique used to pattern high-aspect-ratio microstructures. The quality of the pattern highly relies on the quality of the moulds. This paper describes the surface roughness and geometrical characterization of soft lithography technique for the fabrication of ceramic micro components. Effects of patterning materials and methods on the produced geometry, repeatability and surface roughness were studied and a comparative study was performed for the optimization process. UV lithography of BPR100 and SU-8 and deep reactive ion etching are the methods for fabricating the master mould. In addition, polydimethylsiloxane and Dragon Skin elastomeric have been used in the fabrication of the soft moulds. Mould geometry was inspected using SEM images while surface roughness was measured using stereo imaging. The results show that the maximum obtained thicknesses are 1,000, 250 and 500 μm for SU-8, BPR100 and DRIE moulds. In addition, their surface roughness values are higher than the SU-8. On the other hand, Dragon Skin shows demoulding problems despite it has smoother surface than PDMS mould.     

Development of a dynamic model and study of the dynamic characteristics of an end gas dynamic seal

A significant part of damages in end gas dynamic seals are caused by dangerous vibrations. To improve the reliability of these seals, it is necessary to develop adequate mathematical models and to perform integrated computational and experimental studies. In this article, the two-mass dynamic model for an end gas dynamic seal is considered, which is the most appropriate for practical cases. Theoretical and experimental analyses of the dynamic state of a seal have been performed. The scope of vibration amplitudes and frequencies has been determined for an end gas dynamic seal. The results can be used to design new seals and to implement seals in compressors with magnetic supports.     

A comparative study on CFD simulation of spray penetration between gas jet and standard KIVA-3V spray model over a wide range of ambient gas densities

CFD simulation of spray penetration with standard KIVA-3V were compared with those using both an ‘original gas jet model’ and a ‘normal gas jet profile model that features a new breakup length formula’ by implementing them in the standard KIVA-3V code. The effects of entrainment coefficient on the spray penetration simulated with the gas jet profile were compared to that simulated with the standard KIVA-3V spray model. The accuracy of the CFD simulation results was estimated by comparing them with available experimental data. Both the standard KIVA-3V spray model and the normal gas jet profile model with the breakup length formula predict well the spray tip penetration up to a gas density of 60 kg/m³. The CFD simulation of spray tip penetration with the standard KIVA-3V predicts better with the ‘original gas jet model’ when the ambient gas density is lower than 60 kg/m³. For higher densities, the normal gas jet profile model with breakup length formula predicts the spray penetration better.     

细胞三维动态培养微器件的设计与制作

细胞培养是进行细胞研究的基础,为了在细胞体外培养时提供一种近似于体内的微环境,设计了一种可供细胞三维动态培养的微器件。首先设计了用于输运流体的微通道网络,培养池对称布置于微通道网络中,通过一系列"多进多出"型微通道分别与进样口和出样口相连。利用Comsol软件中的层流物理场和多孔介质物理场耦合对培养池内的流场进行仿真,通过比较流场的均一性和稳定性优化微通道网络结构。然后,采用静电直写技术在培养池内集成聚己内酯(PCL)三维支架,构建细胞三维培养空间。最后,封合微器件,检测微器件培养池内的流体流动情况,并进行细胞实验。实验结果表明,"2×2"型微器件培养池内的流体稳定性和均一性较好;PCL三维支架的纤维间距400μm,纤维直径80μm,孔隙率64%,细胞存活率达到90%以上。该细胞三维动态培养微器件更好地模拟了生物体内细胞生存所需的微环境,培养池内的细胞生长良好,满足设计要求。     

A feasibility study on the design and walking operation of a biped locomotor via dynamic simulation

A feasibility study on the mechanical design and walking operation of a Cassino biped locomotor is presented in this paper. The biped locomotor consists of two identical 3 degrees-of-freedom tripod leg mechanisms with a parallel manipulator architecture. Planning of the biped walking gait is performed by coordinating the motions of the two leg mechanisms and waist. A threedimensional model is elaborated in SolidWorks® environment in order to characterize a feasible mechanical design. Dynamic simulation is carried out in MSC.ADAMS® environment with the aims of characterizing and evaluating the dynamic walking performance of the proposed design. Simulation results show that the proposed biped locomotor with proper input motions of linear actuators performs practical and feasible walking on flat surfaces with limited actuation and reaction forces between its feet and the ground. A preliminary prototype of the biped locomotor is built for the purpose of evaluating the operation performance of the biped walking gait of the proposed locomotor.     

Design of microstereolithography system based on dynamic image projection for fabrication of three-dimensional microstructures

As demands for complex microstructures with high aspect ratios have increased, the existing methods, MEMS and LIGA, have had difficulties coping with the number of masks and fabricable heights. A microstereolithography technology can meet these demands because it has no need of masks and is capable of fabricating high aspect ratio microstructures. In this technology, 3D part is fabricated by stacking layers, 2D sections, which are sliced from STL file, and the Dynamic Image Projection process enables the resin surface to be cured by a dynamic image generated with DMD™ (Digital Micromirror Device) and one irradiation. In this paper, we address optical design process for implementing this microstereolithography system that takes the light path based on DMD operation and image-formation on the resin surface using an optical design program into consideration. To verify the performance of this implemented microstereolithography system, complex 3D microstructures with high aspect ratios were fabricated.     

Novel method for fabrication of polyaniline-CdS sensor for H2S gas detection

In this paper, we report on the performance of a H₂S sensor based on polyaniline-CdS nanocomposites fabricated by a simple spin coating technique. The nanocomposites showed the sensitivity to H₂S gas at room temperature (300 K). The resistance of polyaniline-CdS nanocomposites showed a considerable change when exposed to various concentrations of H₂S. Maximum response up to 48% was achieved for 100 ppm H₂S for PANi-CdS sensor. Depending on the concentration of H₂S, the response time was in the range of 41 and 71 s, whereas the recovery time was in the range of 345-518 s.     

高炉煤气喷雾降温系统的研究和改进

机床的数控改造一般是指对某台普通机床的某些部位做一定的改装,配上经济型数控装置或标准型数控系统,从而使原机床具有数控加工能力。一般是对大型、中型机床以及精密、关键技术和生产中起重要作用的中小型机床进行改造。本文介绍了普通万能工具磨床的数控改造优点及方案。     

气体动压润滑轴承摩擦副材料的选择

论述了气动轴承的应用概况及其摩擦副材料应具备的性质 ,在此基础上提出了多种适用于气体动压润滑轴承的材料。     

气体传感器的动态高精度测试系统设计

目前气体传感动态配气方法已经广泛应用,但具体的配制精度还没有系统研究。设计并组建了以四级杆质谱仪、质量流量控制器和计算机程控系统为主的气体传感器测试系统,该系统根据质谱仪的测试数据利用线性最小二乘法实时调整质量流量控制器的输出电压,采用LabVIEW8.5编写上位机数据采集软件进行远程闭环控制。对目前工业领域使用量最大的12种危化品气体进行了气体配制,并对配制的部分气体利用Agilent6890气相色谱仪进行了测试分析,给出了该测试系统在常温常压下配制不同浓度混合气体的精度。实验数据表明:该系统配制的气体可以作为工业气体传感器的标定气体使用。     

多参数动态气体校准仪的设计与实现

为产生ppb～ppm级微量浓度的高精准校准气体,设计了MFC-2000多参数动态气体校准仪,采用了具有强大功能模块的嵌入式微处理器MC9S12XDT512,完成了气体校准仪的结构及软硬件设计,提出了将臭氧发生器及光度计嵌入在仪器内部,实现了高精度的各种浓度校准气体的产生。试验结果表明,该仪器运行稳定,可靠性好,可以产生100 ppb～6 ppm级的臭氧、二氧化硫等标准气体,并可将产生的臭氧标气直接与NO零气反应产生特定浓度的NO2标气,为监测仪器的校准提供了更为简便的手段。     

Methods of the gas concentration sinusoidal and step changes generation for dynamic properties of gas concentration meters testing

The generation methods of a gas concentration sinusoidal and step changes for dynamic properties assessment of the fast gas concentration meters are described. The need of such fast measurements occurs together with the rising scientists’ interest in contaminants and microorganisms dispersion in the air, especially during the tests of the risk of infection. While the laboratory tests are performed, the tracer gas instead of a infected air is used. Due to the high selectivity, good long-term stability and a wide measurement range, the infrared absorption method for measuring the gas concentration is used. The dynamic properties of this method are limited by the need of the exchange of the gas sample in the measuring chamber. Both constructed generators allow to obtain gas concentration changes with specified amplitude and frequency. The results of step and sinusoidal tests of selected CO₂ concentration meter were compared and they showed a good agreement.     

Analysis of point fabrication model for near-field photolithography with experimental study

For the Gaussian beam, the power density distribution of the aluminum-coated optical tapered fiber probe is discussed and a theoretical fixed-point fabrication model for near-field photolithography is established. The energy density theorem is used to explore the surface exposure of photoresist, which is divided into multiple grids to evaluate the changes in the concentration of photoactive compounds at specific nodes of the interior layer. The full width at half maximum (FWHM) and the contour of the photolithograph following development are then calculated. The fixed-point lithographic experiment and aperture verification of the optic fiber probe are performed to confirm the reliability of the present model, and Dill A, B, C parameters are first measured in this article. According to the experimental results, a better image of the probe aperture can be achieved by increasing the conductivity of the measured articles and reducing the electric charges during the image taken by field-emission scanning electron microscope. The FWHM measured is 166.6 nm, while the measured average probe aperture size is 317.4 nm and the FWHM simulated by the proposed model is 151.3 nm. The error between experiment and simulation is <-9.2%. It is thus concluded that the proposed theoretical model is reasonable and acceptable.