【作者】 钱波；

【导师】 史玉升； 张李超；

【作者基本信息】 华中科技大学 ， 材料加工工程， 2009， 博士

【摘要】 快速成形制造(Rapid Prototyping & Manufacturing)技术是由CAD、激光、精密机械、数控及新材料相结合的一种复合技术，是先进制造领域的发展前沿。在快速成形制造工艺中，普遍存在零件变形、翘曲、坍塌等问题，易导致成形失败，即使加工成功也会对成形后零件质量产生很大的影响。开展快速成形制造关键工艺的研究对于解决上述问题，提高快速成形制造研究水平有重要的意义。为此，本文分别从快速成形制造工艺中的支撑工艺、扫描方式以及扫描系统数据处理三个关键部分进行重点研究，其主要研究内容及结论如下：在支撑工艺研究方面，针对基于STL格式的实体模型支撑区域拾取算法速度慢、效率低且不易识别裂缝等问题。本文提出采用递归方式搜索模型表面来快速拾取支撑区域。具体为利用模型中所有三角面片数据构造拓扑信息，通过面片相邻和边重合关系递归搜索，对每个满足条件的三角面片只搜索一次，因此提高了生成速度，其算法效率达到O(n)，效率高。并能够轻易的识别出STL文件的裂缝，搜索完成后自动生成三维区域轮廓边界环。对于复杂形状的STL模型，针对支撑生成时支撑线与实体模型的相交计算复杂的问题，采用标识计算的原理，实现每条支撑线与其对应三角面片作一次三维相交计算，优化后的算法大幅度提高效率，并在实际中得到检验。以上算法为基础，应用在网格支撑的生成算法中，降低了支撑生成算法的时间复杂度，提高了支撑的生成效率。在扫描方式研究方面，针对逐行或分块变向扫描方式加工复杂零件容易产生应力集中引起翘曲变形的问题，通过采用“基于Voronoi图的螺旋扫描”方式，减少扫描矢量方向和垂直扫描矢量方向上的应力，降低翘曲变形的趋势，然后应用在复杂零件的选择性激光熔化工艺中，解决逐行或分块变向扫描方式加工复杂零件容易引起翘曲变形等关键问题，加工出零部件。针对圆盘型具有内部空腔特征的零件的选择性激光熔化工艺，提出“基于复合环形算法的扫描”方式，该扫描方式能够在每一层熔化成形同时进行预热扫描，解决了逐行或分块变向扫描方式加工圆盘型零件的翘曲变形问题。在快速成形扫描系统数据处理方面，通过对扫描过程中扫描行程和空行程之间的连接过渡进行优化、二维振镜几何校正快速算法、对激光扫描进行延迟处理以及扫描体系采用双线程传送扫描数据等四个方面进行了研究，优化并完善了扫描系统。在选择性激光熔化工艺研究方面：针对加工复杂零部件时易翘曲变形的问题分析，提出了一系列的新型子工艺以及工艺的优化：针对变形累积效应，提出在加工过程中动态改变层厚工艺；针对选择性激光熔化工艺中零件底部添加支撑的问题，研究了体支撑的应用方式和算法；加工方向上，即垂直方向(Z向)和水平方向的摆放问题，对加工方向进行了实验研究，提出在Z向上应保持底部面积大，顶部面积小的正金字塔方向，在水平摆放上应使零件的长边与铺粉辊的运动方向平行；针对复杂零件Z向上有空腔时导致一些层面直接在粉床上熔化易翘曲变形的问题，作者提出一种新型的反变形支架结构来抑制这种变形；最后对于减少零件内应力的退火工艺也进行了简单的研究。通过对上述加工子工艺的实验与应用表明，在加工复杂零部件时能够抑制翘曲变形，保证顺利加工。通过分析上述问题的产生机理，采用对扫描数据进行优化处理、优化支撑工艺、采用上述提出的两种新型扫描方式来解决零件变形、翘曲、坍塌等问题，并在此基础上对金属零件的选择性激光熔化工艺进行研究，提出了若干子工艺，减少选择性激光熔化工艺中的翘曲变形问题，提高选择性激光熔化的研究水平。通过本论文的系统研究，解决了快速成形制造工艺中的一些关键工艺问题，为快速成形制造工艺的完善奠定了基础。更多还原

【Abstract】 Rapid Prototyping is a kind of complex technology which combines CAD, laser, precision machine, CNC with new materials, which belongs to the frontier field of advanced manufacturing technology. In the rapid prototyping production technics, some issues are immanent such as deformation, warping, collapsing and so on which lead to failure. Even if the parts have been manufactured successfully, it will have the big influences on the quality of shaped parts. The research of the rapid prototyping production technics is carried out which plays an important role in solving the above issues and improve the research level of rapid prototyping. In order to solve the above issues, this paper is mainly focused on research of the three key parts including scanning system data processing, scanning strategy and support technics. The main research contents and results are as follows:In rapid prototyping scanning system data processing, two-dimensional scanner geometry correction fast algorithm is proposed, and do the research on deferred processing of laser scanning and so on, meanwhile, scanning system is optimized and completed by optimizing velocity and acceleration in scanning process, optimizing connected transition between scanning stroke and idle stroke, and using pipeline organization in scanning system.On the research of scanning strategy, concerning the problem of producing stress concentration in processing complex parts by progressive scan or changing directon scanning strategy which causes the deformation warping, the helix scanning strategy on the basis of Voronoi diagram is used to reduce the stress in scanning vector direction and vertical scanning vector direction, lower the trend of deformation warping, and then be applied in SLM, meanwhile, solve the crucial issues such as the warping deformation which are easily produced in processing complex parts by progressive scan or changing direction scanning strategy, and produce the complex aviation parts and components. Concerning SLM of the round parts with cavity inside, complex ring algorithm scanning strategy is proposed to preheat and scan when every layer has melted and formed, and solve the warping deformation on processing round parts by progressive scan or changing direction scanning strategy.In the research of support technic, it puts forward many types of support generation algorithm, has analyzed the application characteristics of various types of support, and puts forward rapid recursion area gleaned algorithm through constructing the topology relation among the triangles and edges in STL model, and applies to the generation algorithm of region support. For STL model in complex shape, the generation algorithm of suspension support is presented. Through the analysis of suspension points and geometrical characteristics of the overhang lines, it puts forward a method which can automatically extract the overhang points needing support, support-waiting plane of the overhang lines and the to-support position, consequently, aiming at the complex situation of intersection calculation between support line and STL model when the generation of the regional support, the traditional algorithm is optimized and then the algorithm improve efficiency greatly, finally it is tested in practice.In selective laser melting (SLM) production technic research, based on the analysis of some existing serious problems, especially on the analysis of easily warping deformation problem in the process of processing complex components in SLM, a series of new production sub technic and the technic optimization have been put forward: according to deformation cumulative effects, it puts forward changing the layer thickness of technic dynamically in the process of production; according to the problem of adding support at the bottom of the parts in SLM technic as needed in SLA technic, has studied the application mode and algorithm of body support; according to different production directions in SLM technic, especially on the laid problem in Z direction and horizontal direction, has been studied by the experiment in forming direction, and puts forward keeping large area at the bottom in Z direction and small area on the top which can form into position pyramid direction, and in the level location should make the long side of the parts and the movement direction of powder roller parallelize; according to some layers arising melting and warping deformation in powder bed directly when the complex components have cavity in Z direction, the author puts forward a new kind of backward deformation support production structure to suppress this deformation; finally also has some simple research on annealing technology of reducing the internal stress of the parts.By analyzing mechanism of production of the above issues, optimization process on the scanning data, optimization support technics and two new type scanning strategy are use to solve the above issues which can reduce the deformation of the parts, warping and collapsing. On the basis of the research on selective laser melting (SLM) production technics, some sub-technics are proposed to reduce the warping deformation in SLM, and improve the research level of SLM.Through above-mentioned the experiment of processing sub technic and application, it indicates that it will not cause failure because of warping deformation in the process of making complex components, which can ensure smooth production and improve the surface precision of the parts after production.更多还原