EPS快速成型变向分区域扫描路径的研究

针对目前市场对聚苯乙烯泡沫塑料(EPS)三维切割加工的需要,基于现有的快速成形技术路径扫描策略的特点,结合EPS快速成形的特点,提出一种基于柱坐标的EPS变向分区域扫描路径加工算法,可以有效避免直接扫描方式所造成的过多重复切割。解决了现有EPS快速成型设备不能加工复杂三维模型的能力,实验测试证明,变向分区扫描方式生成的加工算法使得模型加工路径得到优化,提高了系统的加工效率并且减少了加工模型的表面粗糙度。     

选择性激光烧结复合扫描路径的规划与实现

激光扫描路径是选择性激光烧结系统 (SLS)的关键技术之一。针对目前常用激光扫描路径的缺陷 ,提出了基于轮廓环偏移与分区变向填充相结合的一种复合激光扫描路径规划方法。文章给出了这种激光扫描路径的轨迹生成过程、轮廓环的修整、环分组以及环偏移扫描与分区扫描之间的厚度确定方案。并对其中图形运算算法进行了优化。从模拟制造结果可以看到这种激光扫描路径规划方法能够克服其它扫描路径中的一些缺陷     

激光金属沉积成形的扫描方式

扫描方式是激光金属沉积成形(Laser metal deposition shaping,LMDS)制造过程中的关键技术,在分析现有扫描方式及其对成形质量和成形效率影响的基础上,指出现有扫描方式的缺陷,并提出一种基于层面轮廓优化单调区分解的分区平行扫描方式。该方式基于极值顶点可见性原理,对分层后的断面轮廓进行去除内环、非单调多边形的单调剖分等处理,可最大限度地减少分区数量,获得若干个单调子区域。针对各单调子区域采用适应性变间距平行路径填充,可减小扫描线的长度,并保证均匀致密性填充。试验表明这种扫描方式能够提高成形效率和成形质量。     

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。     

基于SLS快速成形工艺的分区域扫描路径研究

在对现有的激光扫描方式进行实验研究和理论分析的基础上，找出了零件产生翘曲变形的原因，提出了一种新的扫描分区方法，从而有效地保证了零件的成形质量。     

激光选区烧结成形机的粉末预热研究

在激光选区烧结（ＳＬＳ）快速成形技术中，粉末的预热是影响成形件性能和成形件精度的重要因素之一，对成形机工作腔的一般预热方法的预热过程进行了分析，研究了辐射预热的热流密度对粉末预热温度的影响，提出了热流密度场模型，并与试验测得的预热温度场进行了比较，该模型对于预热装置设计、ＳＬＳ成形过程控制都具有重要的意义。     

一种基于DSP的数字合成正弦波发生器

介绍一种用新的数字方式发生高精度正弦波的方案，这种方案基于ＳＤＰ（Ｄｉｇｉｔａｌ Ｓｉｇｎａｌ Ｐｒｏｃｅｓｓｉｎｇ）技术，其工作原理和软硬件设计过程都在文中得到了详细叙述。     

基于温度分区的激光沉积成形扫描路径生成方法

现有金属激光沉积成形工件是根据几何模型按照设定扫描路径层层叠加而成,不可避免造成局部热量累积,导致成形工件内部温度梯度大,产生局部应力集中,易引起工件变形开裂。对成形过程温度进行实时检测并实现动态扫描路径规划是解决工件变形开裂的根本途径。在研究不同基体温度对熔宽、熔高影响规律基础上,提出基于层面温度分区的激光沉积成形扫描路径生成方法。采用红外热像仪对沉积层面温度进行实时采集,提取不同温度分区轮廓;提出温度分区轮廓规则化方法,消除局部轮廓尖角,避免过熔覆;改进Weiler-Atherton算法,快速实现分层轮廓与温度分区轮廓的求交运算;针对不同温度分区采用适应性间距生成扫描路径,实现激光沉积成形动态扫描路径规划。试验结果表明：该扫描路径可有效提高成形工件质量。     

非圆光斑对金属激光快速成形的影响及对策

当不同方向扫描成形时,采用相同的扫描间距而忽视非圆光斑各向异性的影响,是造成金属快速成形件内部缺陷的一个重要原因.在不更换或调整原有硬件设备的情况下,采用变扫描间距法(即在不同方向上采用不同的扫描间距)与层间正交变向往复扫描相结合,实验结果表明试件的表面质量、成形精度和内部质量都有显著提高.     

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。     

New kind of subarea-parallel scanning mode for laser metal deposition shaping

A scanning mode is the key technology in a laser metal deposition shaping (LMDS) fabrication process. On the basis of the analysis of existing scanning modes and their influences on the fabrication efficiency and the quality of parts, some disadvantages of them are pointed out. A new kind of subarea-parallel scanning mode for LMDS based on a subdividing profiled outline into monotonous polygon subareas is presented. First, based on the principle of point visibility, inner loops are eliminated, and simple polygons are subdivided into monotonous polygons with the minimal zones. Second, the parallel scanning paths of all monotonous polygon subareas are finished, which diminishes the length of the scanning line. The practical application shows that the scanning mode can enhance the fabrication efficiency and quality. __________ Translated from Chinese Journal of Mechanical Engineering, 2006, 42(10): 170–175 [译自: 机械工程学报]     

基于选择性激光烧结技术的雷达样件快速制造

针对雷达新产品需快速加工出物理样件的研制需求,选择性激光烧结技术作为一种代表性的增材制造技术提供了一条新路径。文中首先结合雷达产品的几类典型需求,分析了选择性激光烧结技术的具体应用情况,包括样件工艺过程分析、直接制造非金属验证件和间接制造金属功能验证件,应用结果表明在缩短样件研制周期方面效果显著。最后,为进一步推动该技术在雷达产品中的应用,提出了当前制约其应用的主要问题及发展方向。     

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.     

Densification of alumina components via indirect selective laser sintering combined with isostatic pressing

To improve the final density of ceramic parts via indirect selective laser sintering (SLS), cold/hot isostatic pressing (CIP/HIP) technologies were introduced into the process. The proposed approach in the present study combined spray drying with mechanical mixing by which we prepared a kind of compound powder consisting of polyvinyl alcohol (PVA, 1.5 wt%), epoxy resin E06 (8 wt%), and alumina so as to get a good fluidity for SLS. At the first step, SLS parts reached the highest relative density of about 32 % when the laser energy density was 0.094 J/mm², which facilitated the next operation and improvement of final density. Then, a soft polymer canning was prepared for CIP around the surface of SLS alumina ceramic parts using pre-vulcanized natural rubber latex RTV-2, gelation and film. Following that, we experimented on different CIP maximum pressure which had different effects on densification of SLS alumina parts, the whole process in CIP was divided into three stages of I, II, and III. Based on thermal gravity curve of epoxy resin E06, ignoring the impacts of the only 1.5 wt% PVA on degreasing, green bodies were degreased and furnace-sintered. Finally, the relative density of alumina parts reached 95.94 % after HIP process. Field emission scanning electron microscopy was used to analyze the densification evolvement in each stage of process and the fracture mechanism. The study showed a positive and practical approach to manufacture ceramic matrix and ceramic components with complex shape by indirect SLS technology.     

基于零件切片的选择性激光烧结预热温度控制方法

选择性激光烧结(Selective laser sintering,SLS)系统是通过加支撑或采用人工调节预热温度的方法来减少成形件的翘曲变形,它劳动强度大、SLS材料浪费多、成形效率低,且预热温度难以精确控制。基于以上情况,提出一种新的控制方法,使预热温度能随零件断面几何形状的变化而自动调节。以华中科技大学开发的SLS设备为研究对象,验证这种新型控制方法的可行性。试验结果和实际应用表明:与原有控制方式比较,根据文中所提出的方法成形的零件表面质量、尺寸精度和形状精度等都有较大幅度改善,并且真正实现了SLS成形过程的自动化。     

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。     

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.     

氧化锆零件激光选区烧结/冷等静压复合成形技术

氧化锆陶瓷材料以其优异的性能在工业生产中具有极大的应用前景,但由于脆性大、硬度高等原因,复杂形状氧化锆零件往往难以成形和加工。为了获得复杂形状氧化锆陶瓷零件,通过溶剂沉淀法将粘接剂尼龙12覆膜至纳米氧化锆粉末的表面,然后对覆膜后的粉体进行激光选区烧结(Selective laser sintering, SLS)成形,并通过传统的冷等静压(Cold isostatic pressing, CIP)技术对SLS零件进行致密化处理,同时满足氧化锆初坯成形时形状复杂度和密度的要求。通过试验得出在激光能量密度为0.415 J/mm2时,获得的SLS陶瓷件密度较大,对不同激光能量密度制备的SLS陶瓷件进行保压压力为200 MPa的冷等静压致密化处理,根据热脱脂机理以及粘接剂的TG曲线,分别制定了SLS/CIP试样的热脱脂工艺,最后对脱脂试样进行高温烧结,在后续处理的各环节,氧化锆零件的密度仍受SLS成形的影响,但该影响逐渐减弱,SLS/CIP/FS成形件最大相对密度和维氏硬度分别达到了97%和1180 HV1,已接近“模压-烧结”的致密氧化锆陶瓷的性能,在试样断口的扫描电子显微镜(SEM)分析基础上,对氧化锆复合成形的微观演变进行了研究。虽然最终烧结件密度和硬度仍有待提高,但是提出了一种极具潜力的氧化锆零件近净成形工艺方法,为制造高性能复杂形状的陶瓷零件奠定了基础。