基于微滴喷射3D打印的纳米颗粒悬浮墨水稳定喷射研究

微滴喷射3D打印工艺中,墨水以单一液滴形式稳定喷射是保证喷墨打印质量的必要条件。但在微滴喷射瞬间,纳米颗粒悬浮墨水的流变学性能会随着剪切速率发生明显变化,对实现墨滴稳定喷射具有重要影响。通过测量墨水黏度与剪切速率之间的关系,建立变黏度喷墨打印有限元模型,并对微滴喷墨打印过程中墨滴黏度、墨滴速度、墨滴形貌的变化规律及影响机理进行研究。得出毛细管力是导致墨滴失稳的重要因素,最后对墨滴稳定喷射进行了数值模拟和物理试验验证,证明毛细管数-奥内佐格倒数(Capillary-ohnesorge reciprocal,CA-Z)纳米颗粒悬浮墨水稳定喷射评价方法的可行性。CA-Z纳米颗粒悬浮墨水稳定喷射评价方法为微滴喷射3D打印墨水的制备及其打印参数的优化提供了理论和试验依据。     

SU-8干膜喷墨腔室的制作工艺研究

描述了一种基于干膜层压技术和光刻技术的制作SU-8干膜喷墨腔室的工艺方法:光刻SU-8胶得到开放腔室并使用氧等离子体处理,将PDMS(Polydimethylsiloxane)上的SU-8干膜层压在开放腔室上,使用光刻技术在干膜层上制作出喷孔,从而得到完整的喷墨腔室。该技术简化了喷墨腔室的制作工艺、缩短了制作周期并且只需要常规设备。文章建立了喷墨腔室结构模型,数值仿真模拟了喷墨过程,优化确定了SU-8干膜喷孔板的厚度。分析了层压参数如层压温度和干膜厚度对键合率和通孔率的影响。使用氧等离子体处理工艺提高干膜的键合强度,优化了等离子体射频功率和处理时间。最后对制作的喷墨腔室进行了键合强度测试。     

压电喷墨打印头聚合物喷孔制作工艺研究

描述了一种压电喷墨打印头SU-8光刻胶锥形喷孔的制作方法。该方法基于接近式曝光工艺和键合工艺,首先在PDMS基底上旋涂SU-8光刻胶,通过控制曝光量、曝光间隙、后烘、显影等工艺参数,得到带有微小锥形喷孔的SU-8光刻胶喷孔板,再将喷孔板与SU-8光刻胶开放腔室层键合,形成压电喷墨打印头腔室。采用耦合压电物理场和层流流场的方法,数值模拟了喷孔形状对喷墨速度的影响,确定了最佳喷孔形状。通过实验,确定了制作SU-8锥形喷孔的工艺参数为:曝光量110 m J/cm2,曝光间隙110μm,后烘60℃、15 min和显影时间3.5 min;并采用30μm孔径的掩模,制作出了大孔孔径30μm、小孔孔径20μm、孔高45μm的SU-8光刻胶微小锥形喷孔。     

压电喷墨腔室键合工艺的研究

描述了一种结合光刻和热键合工艺制作压电喷墨腔室的工艺方法,并对喷墨腔室的键合质量进行研究.首先在Si基底上制作完全交联的SU-8开放腔室,然后在PDMS基底上采用邻近式紫外曝光得到带有锥形喷孔的喷孔板,最后将喷孔板与开放腔室热键合得到一体化的喷墨腔室.通过控制曝光量来得到不同交联程度的喷孔板,测量不同交联程度下喷墨腔室的键合强度;通过优化氧等离子体处理工艺参数,提高了喷墨腔室的键合强度;此外,优化了热键合温度和键合时间,获得最小的腔室变形量.     

基于二氧化硅溅射的PMMA和PDMS亲水改性

为了提高以聚甲基丙烯酸甲酯(PMMA)和聚二甲基硅氧烷(PDMS)为材料的微流体通道的浸润性,通过溅射SiO2对PMMA和PDMS进行了表面亲水改性处理。首先,对PMMA和PDMS进行氧等离子刻蚀,改变其表面形貌;然后,溅射SiO2进行表面亲水改性处理,由不同溅射时间得到不同厚度的SiO2薄膜。在亲水处理后一段时间之内对PMMA和PDMS表面分别进行接触角测量,评价不同条件下的改性效果,并对改性后的样片进行黏接性测试。结果表明:氧等离子刻蚀后,溅射时间10min以上的PMMA表面可在10天内保持极亲水的状态;溅射时间15min后的PMMA在35天之内接触角不超过10°;PDMS的亲水性可保持10天,接触角不超过60°;高温老化处理能延缓PDMS表面疏水性的恢复。实验结果显示:氧等离子刻蚀之后,溅射SiO2的方法可使PMMA和PDMS获得较长时间的表面亲水改性效果。另外,亲水改性处理后的PDMS之间仍可实现有效黏接,改性PMMA与未改性PDMS也能有效黏接。     

激光诱导等离子体加工蓝宝石微结构及其润湿性

激光诱导等离子体刻蚀技术在蓝宝石表面微结构制作方面具有独特的优势。通过控制变量法研究了激光能量密度、靶材和蓝宝石之间的距离和扫描速度对激光诱导等离子体加工蓝宝石微槽的微观形貌和几何尺寸的影响规律。通过正交试验研究了激光诱导等离子体工艺参数对蓝宝石表面微结构接触角的影响,发现扫描线间距对接触角的影响最大,靶材和蓝宝石之间的距离和激光能量密度次之,扫描速度的影响最小。当激光能量密度为6.3 J/cm²,扫描线间距为200μm,靶材和蓝宝石之间的距离为150μm,扫描速度为10 mm/s时,蓝宝石表面微结构的接触角为136°,表现出良好的疏水性;当激光能量密度为7.4 J/cm²,扫描线间距为50μm,靶材和蓝宝石之间的距离为100μm,扫描速度为5 mm/s时,蓝宝石表面微结构的接触角为29°,具有较好的亲水性,并且长时间放置后表面接触角基本保持不变。通过扫描电镜观察发现,蓝宝石表面的微结构上分布着许多纳米颗粒,这些微纳结构共同影响蓝宝石的润湿性。     

水溶性氧化钙陶瓷型芯的挤出式3D打印参数优化与表面精度控制研究

挤出式3D打印成形水溶性氧化钙陶瓷型芯可高质高效成形复杂内腔铸造构件,铸件内腔的残留型芯用水溶解即可快速清理,在复杂内腔构件精密铸造领域具有较大的应用潜力。以针头内径、层高/内径比值、打印速度和内部填充方向四个关键工艺参数进行四因素三水平正交试验,通过对不同工艺参数的3D打印成型坯体进行表面粗糙度测量与统计,采用极差分析确定各个打印参数对坯体表面质量影响的主次顺序,并得到挤出式3D打印氧化钙陶瓷型芯的最优打印参数。结果表明,内部填充方向对型芯坯体表面成形质量有显著的影响,当内部填充方向与外轮廓呈45°和90°时,内部填充浆料与外轮廓层有较多的拐点,拐点处的成形方向发生突变,进而造成挤出压力方向发生突变并作用于外轮廓层,外轮廓层变得凹凸不平,层层堆积成形的坯体表面粗糙度较大、表面质量较差。当针头内径为0.41 mm、层高/内径比值为70%、打印速度为20 mm/s、内部填充方向与外轮廓层平行时,坯体表面粗糙度最小,型芯坯体表面质量最好。通过增加外轮廓层数来可以有效地减小甚至消除填充方向对坯体表面粗糙度的影响,当外轮廓增加至两层时型芯坯体表面粗糙度降低了近22%,这对水溶性陶瓷型芯的快速精...     

自然对流条件下新型亲水涂料的抑霜实验研究

在用自行研制的一种亲水性抑霜涂料制成的亲水表面上进行了不同条件下的抑霜实验研究,同时与以往的抑霜亲水涂料进行了比较,发现在较高环境湿度及较低壁温条件下新型亲水涂料的抑霜效果较以往亲水涂料有明显改善,且成膜更薄,仅为0.06mm;同时研究了环境湿度和冷面温度对新型亲水涂料抑霜效果的影响;另外把这种涂料实际应用于冰箱内壁,长时间运行后,发现抑霜效果相当明显;最后给出了新型亲水涂料抑霜的理论分析.     

离子后处理对TiO2光学薄膜及损伤特性的影响

为了进一步提高TiO_2薄膜的光学特性和激光损伤阈值,采用电子束蒸发技术在K9玻璃上沉积了单层TiO_2薄膜,并用Ar/O混合等离子体对样品进行后处理。通过研究薄膜光谱特性、表面缺陷密度、薄膜表面形貌、薄膜损伤阈值以及薄膜损伤形貌,分析了等离子体后处理时间对TiO_2薄膜激光损伤特性的影响。实验结果表明,随着等离子体后处理时间的增加,薄膜折射率及致密度提高,物理厚度减少,表面粗糙度下降,表面缺陷密度先减少后增加;在1 064nm激光辐射下,TiO_2薄膜的激光损伤阈值从未经等离子后处理的5.6J/cm~2提升至后处理20min的9.65J/cm~2,提升幅度高达72.3%,因此能够更广泛更稳定地应用在激光器中。     

改进跟踪微分器在喷头墨点补偿中的应用

3D打印封装技术是电子封装保护领域的新型工艺，双向打印过程中喷头平移和墨滴喷射之间的相对运动使墨滴实际位置与期望位置产生偏差，影响封装效果。在喷头到达打印位置前一段时间(墨滴飞行时间T_f)喷射可以消除偏差，因此准确获取墨点具体喷射时间至关重要。提出一种改进跟踪微分器估计喷头速度，通过估计的速度值计算采样点到打印位置的移动时间进而得到各墨点喷射时刻，实现喷头墨点补偿。该方法基于位移信息可快速估计速度，有效滤除位置测量时带有的噪声，速度估计比较准确，无需基于对象模型，易于实现。仿真与实验验证该速度估计方法可较准确估计喷头速度值，响应速度较快，有效减小喷头双向打印过程中的墨点偏差，双向打印对准精度在23μm以内。     

Development and ejection behavior of different material-based electrostatic ink-jet heads

There has been growing interests in direct patterning of metallic contents on the surface of the substrate without including complex steps of the microfabrication lithography process. The direct fabrication process using electrostatic ink-jet printing can be expected to be a powerful tool for both nanotechnology research and applications such as microelectronics. The droplet ejection voltage, meniscus, cone-jet behavior, and counter electrode distance depends on the ink properties such as surface tension, viscosity, and percentage of metallic pigments. In this paper, 2-μm level needle-type electrostatic head designs for contact-less fabrication of printed electronics, composed of differently treated surface materials, have been studied and analyzed. The electrostatically actuated ink-jet heads were tested and compared for low power and high resolution on ink containing metallic nano-particle particles as pigments. The two laboratory-fabricated discrete and electrostatically actuated ink-jet heads, one made by poly di-methyl siloxane modeling process and other through micro-electrical discharge machine techniques, were compared, and their orifice outlet surface (hydrophobic and hydrophilic) condition influence has been discussed. The paper also investigates different dripping behaviors of metallic ink under the influence of counter electrode distance, voltages, and materials. The observation of droplet ejection with high-speed camera revealed that in the case of hydrophobic head, better meniscus shape and ejection was achieved even at low voltage compared to the hydrophilic head. It was also found that the less flow rate is required in hydrophobic head. Printing characteristic of the hydrophilic nozzle head was also compared with the hydrophobic head on PET substrate.     

The evaluation of critical pressure ratios of sonic nozzles at low Reynolds numbers

A sonic nozzle is presently used as a reference flow-meter in the area of gas flow-rate measurement. The critical pressure ratio of the sonic nozzle is an important factor in maintaining its operating condition. ISO 9300 suggested that the critical ratio of a sonic nozzle should be a function of area ratio. In this study, 13 nozzles designed according to ISO 9300, with diffuser half angles of 2°–8° and throat diameters of 0.28 to 4.48 mm were tested. The testing result for the angles of 2°–6° are similar to that of ISO 9300. But the critical ratio for the nozzle of 8° decreases by 5.5% in comparison with ISO 9300. However, ISO 9300 does not predict the critical pressure ratio at Reynolds numbers lower than 10⁵. To express the critical pressure ratio of sonic nozzles at low Reynolds numbers, it is found that the critical pressure ratio should be related as a function of Reynolds number rather than area ratio, as used by ISO 9300. A correlated relation of critical pressure ratios and low Reynolds numbers for small sonic nozzles is suggested in this investigation, with an uncertainty of ±3.2% at 95% confidence level.     

Numerical and experimental comparisons of mass transport rate in a piezoelectric drop-on-demand inkjet print head

The analysis of oscillatory fluid flow in a piezoelectric drop-on-demand cylindrical inkjet print head has traditionally been implemented by computationally expensive numerical methods although the print head itself consists of simple shaped components such as a cylindrical tube surrounded by a piezoelectric actuator, and a conical tube for the nozzle part. In a preliminary design stage, it is strongly desirable to save time and effort when simulating the impact of the design on the drop generation. For this purpose, approximate analytic solutions, which describe the fluid motion in an inkjet print head, are developed. Axial velocity history is fed back to a further drop formation simulation with a simplified 1D FDM model. The strengths and weaknesses of the 1D approach are identified. Despite the compactness of the present approach, the results show encouraging agreement of mass transport rate with experimental data.     

基于柔性MEMS皮肤技术温度传感器阵列的研究

采用MEMS皮肤技术,在聚酰亚胺柔性衬底上成功研制出8×8阵列铂薄膜热敏电阻温度传感器。实验采用热氧化硅片为机械载体,以便于旋涂液态聚酰亚胺柔性衬底上器件的加工。最后用湿法腐蚀方法将柔性器件从载体上释放下来。试验表明聚酰亚胺衬底上的铂薄膜热敏电阻与温度的变化具有良好的线性,其电阻温度系数达0.0023/℃。与固态聚酰亚胺膜衬底相比,采用旋涂液态聚酰亚胺解决了制备中遇到的两大主要困难:其一,消除了涂聚酰亚胺衬底与载体界面之间的气泡,聚酰亚胺衬底表面能保持良好平整度;其二,制备过程中由于热循环而使柔性衬底产生的热膨胀明显减小。这种柔性温度传感器阵列易贴于高曲率物体表面以探测小面积温度场分布。     

Free surface transition and momentum augmentation of liquid flow in Micro/Nano-scale channels with hydrophobic and hydrophilic surfaces

We propose a novel micro/nano-scale nozzle structure, featuring an interfacial line between the hydrophilic and the hydrophobic surfaces for a jetting system, such as an inkjet head or electrospray devices. This research will investigate the impact of the interfacial line on flow instability and momentum augmentation as the liquid meniscus moves across the line. The research methods used in this paper, in respect to micro-and nano-scale channels, are computational fluid dynamics (CFD) and non-equilibrium molecular dynamics (MD), respectively. With the growing interest in micro/nano electromechanical systems (MEMS/NEMS), many studies have been conducted to develop an advanced micro/nanofluidic system. However, until now, there have been few in-depth studies on passive flow control in micro and nano nozzles using the hydrophilic and hydrophobic surface characteristics. In this research, the sequential arrangement of hydrophilic and hydrophobic surfaces in the nozzle is presented along with an investigation into how flow instability and momentum augmentation are going to be applied to an efficient micro/nano jetting system. When a liquid meniscus arrives at the interfacial line between hydrophilic and hydrophobic surfaces, the meniscus shape changes from concave to convex and the fluid motion near the wall stops until the concave shape is fully converted. Because the momentum should be conserved, the lost momentum near the wall transfers to the center region, and therefore the liquid at the center region is accelerated as it crosses the line. If we use this nozzle structure and the augmentation of the momentum near the center, a tiny droplet can be easily generated. This paper was recommended for publication in revised form by Associate Editor Haecheon Choi Doyoung Byun received the B.S., M.S, and Ph.D. degrees in school of mechanical and aerospace engineering from the Korea Advanced Institute of Science and Technology (KAIST), Taejon, Korea, in 1994, 1996, and 2000, respectively. From 2000 to 2002, he was in the Korea Institute of Science and Technology Evaluation and Planning as a Senior Researcher. In 2003, he joined the faculty of the School of Mechanical and Aerospace Engineering, Konkuk University, Seoul, Korea. His current research topics are development of electrohydrodynamic inkjet head, microfluidic devices, and biomimetic robot systems. His research interests include microfluidics, MEMS, and biomimetics.     

具有电磁阀微喷功能的3D打印机构建及应用

3D打印技术已经在生物医学、传感器制造等领域得到广泛应用。然而,传统3D打印机由于自身工作方式的不同,适用范围不同,难以同时兼容生物制备和传感器制备。因此,以电磁阀作为3D打印机的喷头,自主设计并构建具有独特工作方式的3D打印机,将高精度液滴分配方式应用于3D结构打印。研究料筒气压、电磁阀开关时间、喷头高度对打印液滴直径的影响,并对点、线、网、面图案的打印质量进行评估;利用所构建的打印机制备具有真皮乳头结构的组织工程皮肤和阵列式柔性压力传感器,测试组织工程皮肤的细胞活性及压力传感器的压-阻转换特性。结果表明,打印液滴直径尺寸与料筒气压、喷头开启时间、喷头高度均成正相关;3D打印机对点、线、网、面图案的打印效果较为理想;可成功应用于具有真皮乳头结构的组织工程皮肤和柔性压力传感器的制备。所构建的3D打印机融合喷墨式打印机和挤出式打印机的优势,对打印墨水有较好的兼容性,具有打印方式简单、打印速度快、成型质量高的优点,对组织工程皮肤及柔性压力传感器的研究具有重要意义,为实现具有感知功能仿生皮肤的制备奠定基础。     

核电封头五轴数控加工刀具路径规划研究

核电封头机械加工余量大,并且球面上非对称的分布这若干管嘴端面,这给高效刀具路径规划造成了极大的难度。在NURBS方法基础上,针对核电水室封头等形状复杂大型工件,从加工效率和稳定性的角度,建立环形铣刀加工曲面的运动几何学模型并应用加工域规划法进行刀具路径规划。合理的刀具路径规划可以有效的避免刀具干涉,缩短刀具路径,提高加工精度。     

圆管式压电喷头的液体分配

针对用于喷墨打印的圆管式压电喷头建立了计算模型,并且根据它的驱动特点选择了合适的边界条件。介绍了仿真软件针对自由表面流动问题的计算原理。然后,以乙二醇水溶液为例,计算了压电喷头分配该溶液的分配过程;利用液滴成像系统获取了不同时刻的液滴图像,验证了建立的模型和数值算法的正确性。最后,计算了压电喷头在不同输入位移、不同黏度以及不同表面张力下的液体分配过程。仿真结果显示:液体分配性能与激励位移密切相关,在72.5mN/m的表面张力作用下,10nm的输入位移很难分配黏度为4.0mPa·s的液体,而15nm的输入位移在分配黏度为4.0mPa·s液体时却能够产生卫星液滴。因此,对于某种液体寻找一个合适的激励条件非常重要,过小的激励产生不了液滴,过大的激励则会产生较大甚至多个卫星液滴;增大黏度会延缓或阻滞液滴形成过程,增大表面张力却能加快液滴形成过程。本文的计算方法对于研制新式喷头或者研究喷头的喷射能力均具有指导意义。     

Adaptive rapid prototyping/manufacturing for functionally graded material-based biomedical models

In this paper, research on developing adaptive rapid prototyping/manufacturing (RP/M) algorithms for functionally graded material (FGM)-based biomedical models is reported. Non-uniform rational B-spline and FGM-based features have been proposed to present the models. Innovative algorithms for tool path optimization in RP/M have been developed, including: (1) a mixed tool path algorithm to generate contour/offset tool paths to represent varying material composition along the boundary of each sliced layer of a model and zigzag tool paths to present the internal area of a single material to simplify computing and processing and (2) adaptive algorithms to control the RP/M nozzle/print head to minimize the build time of each sliced layer according to the geometrical characteristics of the model. Case studies of FGM-based biomedical models have been used to verify and demonstrate the performance of the research in terms of algorithm effectiveness.     

The use of post‐mortem Raman spectroscopy in explaining friction and wear behaviour of sintered polyimide at high temperature

Due to their thermal stability and high strength, polyimides are an aromatic type of polymer that is used in sliding equipment functioning under high loads and elevated temperature. However, its tribological behaviour under high temperature and atmospheric conditions is not fully understood. It has been reported that a transition from high towards lower friction occurs ‘somewhere’ in the temperature region between 100°C and 200°C; however, a correlation with changes in the polyimide molecular structure remains difficult to illustrate and it is not certain whether or not this transition is correlated to lower wear. In the present work sliding experiments under controlled bulk temperatures between 100°C and 260°C are performed. A transition is observed in both friction and wear at 180°C which is further explained by microscopic analysis of the transfer film on the steel counterface and Raman spectroscopy of the worn polymer surfaces. A close examination of the spectra reveals transitions in relative intensity of certain absorption bands, pointing to different orientation effects of the molecular conformation at the polymer sliding surface at 180°C. Copyright © 2006 John Wiley & Sons, Ltd.