面曝光快速成形系统中涂层技术的研究

针对面曝光快速成形系统对涂层工艺的要求,设计了一种浸入式涂层系统。该系统由步进电动机、丝杠、刮刀、导轨等组成。为了研究涂层参数对涂层性能的影响,建立了涂层厚度模型,通过试验比较同一涂层参数取不同值时涂层厚度的变化规律。试验结果表明:涂层厚度随刮刀间隙及刮削次数的增大而增大;涂层厚度随刮削速度的增大而减小。为了观察涂层厚度是否随制件高度的增加而变化,制作了高40 mm的台阶制件并测量其涂层厚度。测量结果表明:在所设计的浸入式涂层系统中,涂层厚度不随制件高度的增加呈现明显的变化趋势。     

光固化快速成形中树脂涂层技术研究

分析光固化快速成形对树脂涂层技术的要求及对成形工艺,制件精度,成形效率的影响。并根据液态树脂的物性,分析现有激光快速成形机中各种树脂再涂层方法的特点,提出一种瀑布式树脂再涂层方法。     

高分辨率激光快速成形系统研究与开发

开发了一种新型激光快速成形系统。利用该系统可制作尺寸范围为65 mm×65 mm×150mm的制件原型。 该系统由He-Cd单模激光器、小光斑扫描系统、新型树脂涂层系统及控制系统组成。由扩束镜、高精度扫描振镜 及f-θ透镜构成扫描系统,扫描面上的激光光斑直径达到0.012 mm。由蠕动泵、高精度工作台、树脂槽及刮刀组 成新型精密树脂涂层系统,树脂涂层厚度达到0.02 mm。利用该系统制作了具有微流道的滴灌器件及其他微型零 件的原型。     

光固化快速成形技术中的精度研究

结合激光快速成形ＬＰＳ－６００Ａ系统论述光固化法快速成形技术中的精度概念，分析影响度的各种因素及改善制件精度的途径，讨论原型制件精度的评价标准问题。     

光固化快速成形精度影响因子的优化

为提高快速成形工艺的精度，利用Taguchi方法对影响扫描平面内成形精度的主要因子（扫描速度、线宽补偿、树脂收缩补偿系数及扫描间距），进行了优化实验研究。通过对实验结果的信号干扰比进行方差分析，发现扫描间隔、线性收缩补偿系数以及扫描速度与扫描间隔的交互作用对扫描平面内制作精度有显著影响，扫描速度与线宽补偿的交互作用及扫描速度与线性收缩补偿的交互作用对制作精度有一定的影响。针对高分辨率激光快速成形系统，得出了以扫描平面内制作精度为优化目标的制作参数的最佳组合。验证实验结果表明，最佳制作条件下制件的误差已减小到3μm，表明最佳因子组合方案是合理可行的，该参数的最佳组合可显著提高制作精度。     

对SLS覆膜砂制件抗压强度的研究

主要对覆膜砂的激光烧结快速成形进行了实验研究.系统分析了激光功率、扫描速度、扫描间距、铺粉厚度对成形制件抗压强度的影响.最后得出了最佳成形工艺参数.实验结果对于提高制件的抗压强度有指导意义.     

对SLS覆膜砂制件抗压强度的研究

主要对覆膜砂的激光烧结快速成形进行了实验研究。系统分析了激光功率、扫描速度、扫描间距、铺粉厚度对成形制件抗压强度的影响。最后得出了最佳成形工艺参数。实验结果对于提高制件的抗压强度有指导意义。     

熔融沉积快速成型工艺参数对阶梯效应的影响

目前快速成型制件的成形精度制约着该技术的推广和发展,对于给定的设备,设置不同的工艺参数将会对最终模型的成形性能、制件精度和质量等构成较大差异。分析了FDM快速成型技术的成型原理和特点,研究了分层厚度和成形角度对阶梯效应的影响。     

尼龙6/铜复合粉末选区激光烧结制件翘曲研究

通过大量的对尼龙6/铜复合尼龙粉末烧结试验,研究不同工艺参数,如激光功率、铺粉厚度以及扫描速度对制件翘曲程度的影响,并采用翘曲高度法来表征翘曲程度。根据试验数据绘出了尼龙制件翘曲程度随各工艺参数的变化曲线,总结出了制件翘曲程度随各工艺参数变化的趋势。     

尼龙6/硅灰石混合粉末选区激光烧结成型精度研究

收缩是尼龙材料选区激光烧结成型的常见问题,不均匀的收缩将导致翘曲变形。影响成型精度的因素很多,包括材料本身的特性,烧结工艺参数等。本文通过添加硅灰石来提高尼龙材料的成型精度,用翘曲高度法分析了制件翘曲高度随硅灰石用量和烧结工艺参数,如激光功率、预热温度变化的规律。     

树脂超声处理的新型涂层技术研究

为提高快速成形系统中堆积方向的制作分辨率,研究了光敏树脂的黏度、表面张力及固液两相接触角随超声处理时间和功率的变化规律。试验结果表明:LPR2001型光敏树脂在超声处理开始的2~5min,树脂的黏度、表面张力及接触角迅速减小;随处理时间延长,以上树脂特性值随之回升;超声功率在40~50W时,树脂的黏度、表面张力及接触角减小幅度最大。对光敏树脂超声处理前后能实现的最小涂层厚度进行了实验对比,结果表明:超声处理的树脂能将最小涂层厚度由原来的0.02mm降低到0.01mm。     

Development of a high–resolution rapid prototyping system for small size objects

A high-resolution stereolithography (SL) system for fabricating small objects with complex microstructures has been developed. This novel SL system consists of a single mode He-Cd laser, an improved optical scanning system, a novel recoating system and a control system. A laser light spot with the diameter of 12.89 μm on the focal plane is obtained with the improved optical scanning system, and resin layers with the thickness of 20 μm can be built with the novel recoating system. Experimental studies were carried out to investigate the influences of the build parameters on the cured line width and depth with this novel SL system. The experimental results showed that the cured depth and width increase with the increasing ratio of laser power to scanning speed. And it is found that the cured line built using the high-resolution SL system is smaller in width and deeper in depth compared with the cured line fabricated in conventional SL system under the same scanning conditions. Based on the cured line width and depth obtained in the experiment, empirical equations predicting the cured line width and depth according to the ratio of laser power to scanning speed are established using a least-square fitting. The cured line width and depth predicted by the empirical equations provide a foundation to set up accurate line width compensation and appropriate layer thickness in the high-resolution SL system. Some small objects with microstructures have been fabricated with the new SL system.     

Determination of process parameters in stereolithography using neural network

For stereolithography process, accuracy of prototypes is related to laser power, scan speed, scan width, scan pattern, layer thickness, resin characteristics and etc. An accurate prototype is obtained by using appropriate process parameters. In order to determine these parameters, the stereolithography (SLA) machine using neural network was developed and efficiency of the developed SLA machine was compared with that of the traditional SLA. Optimum values for scan speed, hatching spacing and layer thickness improved the surface roughness and build time for the developed SLA.     

用于高精度小尺寸零件制作的光固化快速成型技术的现状与发展

用于高精度小尺寸零件制作的光固化快速成型技术源于快速原型技术 ,利用光诱导树脂固化 ,实现逐层堆积的原理制作零件原型。本文回顾了近年来该领域中开发出的主要工艺方法、原理及系统构成 ;本文还提出了以变形反射镜器件为核心构建新型动态视图发生器 ,采用整层曝光固化工艺实现原型快速制作的新方法。和其它方法使用的动态视图发生器相比 ,本文提出的新型动态视图发生器具有更高的分辨率和更高的对比度 (可达 10 0 0∶1)。     

Mass production of 3-D microstructures using projection microstereolithography

Microstereolithography (MSL) technology is derived from the conventional stereolithography process and can meet the demands for fabricating complex 3-D microstructures with high resolution. This technology can be divided into scanning and projection methods, which have different levels of precision and fabrication speeds. Scanning MSL fabricates very fine 3-D microstructures by controlling the position of the laser spot on the resin surface. Projection MSL quickly fabricates one layer with one exposure using a mask. In this paper, we propose a projection MSL system with uniform illumination and image formation based on optical design for fabricating microstructure arrays. This system can realize mass production of 3-D microstructures in the meso-range, which falls between micro-and macro-ranges, with a resolution of a few microns. Microstructure arrays were fabricated to verify the performance of the proposed system.     

Control of melt pool temperature and deposition height during direct metal deposition process

This paper presents a hybrid control system that is able to improve dimensional accuracy of geometrically complex parts manufactured by direct metal deposition process. The melt pool height is monitored by three high-speed charged couple device cameras in a triangulation setup. The melt pool temperature is monitored by a dual-color pyrometer. A two-input single-output hybrid control system including a master height controller and a slave temperature controller is used to control both height growth and melt pool temperature at each deposition layer. The height controller is a rule-based controller and the temperature controller uses a generalized predictive control algorithm with input constraints. When the melt pool height is above a prescribed layer thickness, the master height controller blocks control actions from the temperature controller and decreases laser power to avoid over-building. When the melt pool height is below the prescribed layer thickness, the temperature controller bypasses the height controller and dynamically adjusts laser power to control the melt pool temperature. This hybrid controller is able to achieve stable layer growth by avoiding both over-building and under-building through heat input control. A complex 3-D turbine blade with improved geometrical accuracy is demonstrated using the hybrid control system.     

Improving Stereolithography Part Accuracy for Industrial Applications

High dimensional accuracy and part stability are significant elements of the end product in rapid prototyping technology (RPT) processes whether it is a component or a tool. However, in most cases, models built in acrylic-based resin in the stereolithography (SL) process have not been of the desired quality and this has led to the use of more expensive resins that have a longer build time. An experimental investigation has been carried out to determine statistically the optimum build parameters to be used in the Taguchi method, to improve the SLA product quality. The two new hatch styles developed in this study have resulted in an overall improvement of the part accuracy, and a new layer thickness for part building in stereolithography has been proposed.     

Multiple fabrications of sacrificial layers to enhance the dimensional accuracy of microstructures in maskless projection microstereolithography

Microstereolithography (MSL) is a promising technology for producing fully three-dimensional microstructures with overhanging features and high-aspect ratios. In conventional stereolithography (SL), a layer thickness of ≈50–100 μm is obtained by using a recoater. However, a recoater cannot be used in MSL, where the layer thickness is typically ≈10 μm or less, since resin flow may break or distort the pre-fabricated layers. In most MSL systems, the resin surface (or layer thickness) is controlled by a free surface technique that employs resin gravity to refresh the resin surface over a given settling time. In addition, a sacrificial layer must be fabricated in MSL to create a flat initial surface and provide support, just as in SL. In this paper, the fabrication methodology and functionality of the sacrificial layer is investigated for microstereolithography microstructures fabricated using the free surface technique. Experimental data are presented that indicate the greater the number of sacrificial layers, the sharper the dimensional accuracy of the microstructures in the building direction. This is because multiple fabrications of the sacrificial layer affect the resin ‘wetting’ status on the substrate or pre-cured surfaces. Several microstructures were fabricated to verify the effect of multiple fabrications of the sacrificial layer on dimensional accuracy in the building direction.     

Accelerating fabrication speed in two-laser beam stereolithography system using adaptive crosshatch technique

The aim of this research is to develop a novel two-laser beam stereolithography system. The wavelengths of the two semiconductor laser beams are determined to be 405 nm (blue light) and 532 nm (green light), respectively, according to the relative absorbance rate of used visible light curable resin. The blue light laser is suitable for scanning contour of objects because of its fast absorbance, thus giving a narrow cured depth. The green light laser is better suited for scanning the internal crosshatch for condensing the fabrication time because its high power results in a wide cured width and deep penetration. The influence of the photoabsorber, carbon powder with average diameter of 0.1 µm, is discussed and an optimal weight percentage of 1.5 is specified for controlling cured thickness. An adaptive crosshatch technique is introduced and applied to the fabrication process. In addition, a turbine is fabricated using the proposed approach for comparison with the E-DARTS system in terms of fabrication capability. Results show that the developed system can fabricate objects quickly with high accuracy.