板料激光曲线弯曲成形温度场的数值研究

板料激光弯曲成形是一种利用激光成形构件的柔性成形技术。以矩形板激光单次扫描成形的过程为研究对象，通过对有限元分析软件ANSYS进行二次开发，建立了基于扫描路径的动热源模型，并系统研究了各技术参数下激光弯曲温度场的动态变化。分析发现：（1）曲线扫描准稳态过程的温度峰值要小于同工况下直线扫描情况，且持续时间短暂，温度峰值不断跳跃；（2）相同工艺参数下，随着扫描路径曲率的增大，温度峰值及加热区温度梯度均减小，当扫描路径曲率继续增大时，温度峰值及加热区温度梯度却随之增大；（3）提高激光功率，降低扫描速度以及在恒定线能量密度下增大扫描速度，均使板料温度梯度增大，而增大光斑直径，温度梯度减小。     

激光分形烧结快速成形装置的研制

根据激光分形烧结快速成形要求其扫描过程中无反向间隙和高分辨率的要求,设计并研制出了由钢丝绳牵引驱动的二维扫描工作台,铺粉装置,激光器,计算机控制系统组成的激光分形扫描快速成形系统。     

板料激光正弦扫描成形研究

板料激光弯曲成形是一种利用激光成形工件的柔性成形技术。研究激光成形过程中板料变形与扫描路径之间的关系对该技术的应用尤为重要。文章以板料激光扫描成形过程为研究对象,对激光曲线扫描中较为普遍的正弦路径进行了有限元模拟分析。结果表明,在相同工艺参数下,正弦扫描时,光斑在板料边缘停留时间相对较长,温度峰值攀升更为迅速;由于板料成形中只受热应力作用,变形区域的形状、大小与扫描路径有关。由于约束的影响,正弦扫描成形时,板料加热区表现为一个半径较大的圆弧状区域,并且由于板料中间部位受到的刚端抑制作用相对较大,使两端产生翘曲。随着弦高的减小,翘曲现象减轻,渐呈准直线。     

激光立体成形TC4钛合金的热力场演化

激光立体成形能够实现高性能复杂零件的精确成形,但成形过程中的高温度梯度极易导致残余应力和变形,最终影响构件的几何精度和力学性能。通过搭建基板单边夹持原位热变形测量系统,探究了多道多层TC4钛合金成形件在激光立体成形过程中基板温度、变形的演化规律,分析了不同扫描策略对构件热应力场的影响。研究结果表明,构件的变形发展受其热历史驱使,扫描策略对成形件的热变形具有显著影响。     

尼龙材料的选区激光烧结性能试验研究

选取国产PA1212材料，采用选区激光烧结(Selective Laser Sintering，即SLS)快速成形技术快速制作尼龙材料原型，分析了烧结过程中激光与尼龙材料作用的物理过程，重点阐述了预热温度、激光功率、扫描速度、扫描间距与铺粉参数等因素对尼龙材料烧结成形质量的影响，确定了合适的SLS工艺参数。     

选择性激光烧结新型扫描方式的研究及实现

选择性激光烧结（Ｓｅｌｅｃｔｉｖｅ　ｌａｓｅｒ　ｓｉｎｔｅｒｉｎｇ，ＳＬＳ）快速成形技术是近１０年来发展起来的一种先进制造技术，采用此项技术可以显著地缩短产品投放市场的周期，降低成本，提高产品质量，增强企业的竞争能力。而扫描方式是ＳＬＳ成形过程中的一项关键技术，在分析了现有扫描方式及其对ＳＬＳ制件精度、强度以及成形速度影响的基础上，指出了现有扫描方式的缺陷。为了克服这种缺陷，特提出并实现了一种新的分区变向扫描方式及其分区算法，它通过将扫描线段进行分组，以避开截面内孔和凹槽。这种新的分区变向扫描方式及其算法已经成功地应用到华中科技大学开发的ＨＲＰＳ系列ＳＬＳ系统中。实际应用表明：这种新型扫描方式能大幅度地提高烧结成形效率和减小烧结体的翘曲变形量。     

快速成形自适应扫描路径的研究与实现

结合激光金属沉积成形工艺和现有平行扫描路径生成方法分析了局部过熔覆或欠熔覆问题的根本成因.提出了一种自适应扫描路径生成方法,首先采用特征点和特征边识别的适应性扫描间距生成扫描填充线;然后提出基于待定过渡线中点和特征边位置关系判断来优化连接填充矢量生成扫描路径.应用表明,自适应扫描路径有利于成形质量的提高.     

薄壁件激光熔覆增材制造扫描策略试验研究

激光熔覆增材制造技术可以加工更复杂的零部件,具有广阔的应用前景。环形薄壁件是典型的复杂零部件,激光扫描策略对此类零部件成形质量具有重要影响。以Fe313为熔覆材料,设计了4种激光扫描策略。结合试验研究,分别从环形薄壁件顶端平整性、显微组织性能以及显微硬度三个方面研究了激光扫描策略对环形薄壁件成形质量的影响规律。研究结果表明:激光同向扫描策略优于激光反向扫描策略,而激光变点同向扫描策略优于激光定点同向扫描策略。     

金属粉末激光成形扫描方式

将扫描线断面轮廓形状近似看作一段圆弧、以相邻扫描线重叠面积与凹沟面积相等为原则确定扫描线间距。对分区扫描和环形扫描两种扫描方式进行分析和比较,环形扫描方式明显减少激光光闸开关次数、系统稳定性和零件成形精度提高,但是相邻扫描线间浸润性差、沟壑较深,而分区扫描方式扫描间距稳定单一、浸润性好、沟壑较浅,但是激光光闸开关频繁、空跳次数较多。改进扫描方式,将变向分区扫描方式与环形扫描方式相结合加工出无缺陷、全密度金属功能零件。     

厚钢板激光多次扫描弯曲成形的研究

采用数值模拟和实验研究分析了厚钢板激光多次扫描弯曲成形过程中弯曲角度与激光扫描次数之间的关系。建立三维热力耦合有限元模型计算了成形过程的温度场、应力场和弯曲角度的变化,对不同厚度钢板的激光多次扫描弯曲成形过程进行了实验研究,模拟结果与实验结果符合较好。在相同的工艺参数条件下,钢板越厚,弯曲角度越小。钢板弯曲角度随激光扫描次数的增加而增大,但对不同厚度钢板,它们的变化规律不同。钢板下表面的应变强化是多次扫描过程中随扫描次数增加而弯曲角度增量减小的主要原因。     

Influence of process parameters on part shrinkage in SLS

Shrinkage, one of the typical phenomena in the selective laser sintering (SLS) process, affects the final dimensional accuracy of SLS products. We investigated the relationship between the shrinkage and the process parameters of SLS in order to improve dimensional accuracy. According to the characteristic of SLS, the following process parameters are considered: layer thickness, hatch spacing, laser power, scanning speed, temperature of working environment, interval time and scanning mode. A neural network model on the relationship between the processing parameters and shrinkage was built on the basis of a series of experiments. The experimental investigation results show that the neural network model is possible to be used to predict the effects of the process parameters on the shrinkage with reasonable accuracy and to analyze the relationship between the shrinkage and the process parameters of SLS quantitatively. So it is suitable to apply neural networks approach to study the SLS process. This model will allow us to produce the SLS parts with the desired quality attributed by selecting the appropriate parameter values prior the processing. This paper proposes a promising approach to improve the accuracy of the SLS part.     

Optimizing process parameters for selective laser sintering based on neural network and genetic algorithm

Selective laser sintering (SLS) is an attractive rapid prototyping (RP) technology capable of manufacturing parts from a variety of materials. However, the wider application of SLS has been limited, due to their accuracy. This paper presents an optimal method to determine the best processing parameter for SLS by minimizing the shrinkage. According to the nonlinear and multitudinous processing parameter feature of SLS, the theory and the algorithms of the neural network are applied for studying SLS process parameters. The process is modeled and described by neural network based on experiment. Moreover, the optimum process parameters, such as layer thickness, hatch spacing, laser power, scanning speed, work surroundings temperature, interval time, and scanning mode are obtained by adopting the genetic algorithm based on the neural network model. The optimum process parameters will be benefit for RP users in creating RP parts with a higher level of accuracy.     

SLS翘曲变形计算与扫描方式优化

选择性激光烧结工艺(selective laser sintering,SLS)加工中所产生的翘曲变形严重影响了成型件的加工精度和SLS技术的应用与推广。本文在研究SLS成型误差的基础上,分析造成SLS成型件翘曲的主要原因与产生的机理,构建了一种新的翘曲变形的力学模型。并以此模型为基础,分析了现有SLS扫描方式存在的不足,提出一种新的间隔式激光光栅扫描方式。通过实验验证,该扫描方式可以有效地降低SLS成型件的翘曲变形,提高SLS成型件的加工精度,而且能大大提高加工速度,降低加工能耗。     

选择性激光烧结方法加工仿生支架的工艺研究

在利用选择性激光烧结技术加工仿生支架过程中,加工参数(包括激光功率、扫描速度、扫描间距)是影响成形质量的重要因素,通过调整加工参数可以使成形零件内部保持一定的孔隙,从而产生支架内部微孔结构。正交试验方法可以科学地安排和分析多种因素的影响,从而优化加工参数,最终获得具有较高孔隙率的仿生支架。     

SLS快速成形技术中激光加工参数对制件性能的影响

以AFS--320MZ快速成形机为例，研究了基于选择性激光烧结(SLS)快速成形制造中激光功率密度、扫描速度、扫描间距、扫描方式和铺粉密度等加工参数对制件性能的影响。     

Three-Dimensional imaging of fertilization and early development

The field of biological microscopy has recently enjoyed major technical advances, exemplified by the development of field-emission low-voltage scanning electron microscopes and laser scanning confocal light microscopes. In addition, computer processing of microscopical data is revolutionizing the way morphological information is imaged. In this paper, we illustrate methods by which this new technology can be used to examine events in fertilization and early development in three dimensions. Different types of specimen preparation protocols, using both echinoderm and mammalian gametes and embryos, are evaluated for their ability to preserve accurately the threedimensional organization of these specimens for imaging by both low-voltage scanning electron microscopy and laser scanning confocal light microscopy.     

Building Porous Biopolymeric Microstructures for Controlled Drug Delivery Devices Using Selective Laser Sintering

The capability to build parts with predetermined porous microstructure and dense walls using powdered biomaterials makes selective laser sintering (SLS), one of the more flexible rapid prototyping (RP) process, a strong candidate for building biodegradable controlled release drug delivery devices (DDD). The objective is to design a varying-porosity circular disc with outer region being denser acting as diffusion barrier region and inner more porous region acting as drug encapsulation region. This is to achieve a zero-order of release over a desired duration of time in drug administration.A key study in this paper was to determine the influence of critical SLS process parameters namely, laser power, laser scan speed and part bed temperature on dense wall formation and control of the porous microstructure of SLS-fabricated parts built with biomaterials. The physical characteristics of the fabricated devices were investigated through microstructure examination using the scanning electron microscope (SEM). Two biodegradable polymers, namely Polycaprolactone (PCL) and Poly (-L) Lactic Acid (PLLA), were investigated. For PCL varying-porosity disc, the laser power is set at 3 W (inner region) - 4 W (outer region), the scan speed at 5080 mm/s and the part bed temperature at 40°C. For Poly(-L) Lactic Acid (PLLA), the laser power is set at 12 W, the scan speed at 1270 mm/s and the part bed temperature at 60°C. With the set of SLS parameters tabulated for specific polymers, polymeric matrix with specific porosity can be fabricated as drug delivery devices.     

Positional correction algorithm of a laser galvanometric scanning system used in rapid prototyping manufacturing

The laser galvanometric scanning technique has brought rapid prototyping manufacturing into a new era. However, a number of errors severely affect the prototyping accuracy of the work piece. This paper gives a detailed analysis of the errors involved in the galvanometric scanning system used in rapid prototyping manufacturing. A positional correction algorithm has been developed to rectify the errors to meet the precision requirements of the processing. Experimental results based on a selective laser stinting (SLS) machine prove the efficiency of the positional correction algorithm.     

激光选区烧结超高分子量聚乙烯工艺及性能

研究了激光选区烧结(SLS)成型工艺中不同工艺参数以及后续热处理工艺对超高分子量聚乙烯(UHMWPE)材料成型性能的影响。通过调整扫描间距、激光功率、扫描速度等不同工艺参数,描述了SLS成型UHMWPE零件的致密度、拉伸强度以及断裂伸长率,并对热处理前后的SLS成型UHMWPE零件的力学性能进行了比较。结果显示,致密度、拉伸强度、断裂伸长率总体上与激光功率呈正相关关系,与扫描间距、扫描速度呈负相关关系。经热处理后,SLS成型UHMWPE零件的力学性能有明显提高,致密度达到95.12%,抗拉强度达到24.08 MPa,断裂伸长率达到334.82 MPa。实验结果表明:SLS成型UHMWPE零件与模塑成型UHMWPE零件性能尚有差距,仅优化成型工艺不足以得到理想性能,但经热处理后,零件性能基本满足使用要求。