【作者】 苏旭彬；

【导师】 杨永强；

【作者基本信息】 华南理工大学 ， 机械电子工程， 2011， 博士

【摘要】 选区激光熔化(SelectiveLaserMelting,SLM)成型技术是当前主要的可以直接制造金属功能件的快速成型(RapidPrototyping,RP)技术之一。SLM可以获得冶金结合、致密组织、高尺寸精度和良好力学性能的功能件,是近年来RP的研究热点和发展趋势。目前对SLM的研究主要集中在材料工艺、设备和应用,对成型件设计的研究相对较少,并且多用于单零件的直接制造,鲜有涉及机构件的直接制造。据此,本文研究基于选区激光熔化的功能件数字化设计与直接制造,主要内容及结果如下:(1)研究了功能件的自由结构设计。构建了功能件的结构设计框架,在此基础上分析了结构元素之间的设计时序关系。从激光深穿透、模型分层和光斑尺寸三个方面研究了自由结构设计的原理约束,进而建立了功能件自由结构设计的规则,规则包括原理约束和基本自由结构。在规则指导下,功能件可进行具有非标准原材料形状、无刀具特征、无装夹结构、自由孔结构或自由表面等特点的结构设计。(2)根据热力学原理和粉末堆积体的几何特性,推导了SLM成型过程的能量利用率公式及其修正系数;根据层间互错扫描方式下熔道之间的几何关系,提出了层内搭接机制、层间搭接机制和混合搭接机制三种熔道搭接机制。研究了扫描间距和扫描速度对成型件致密度的影响,并测试了SLM成型件的力学性能,结果表明,SLM成型件的抗拉强度和屈服强度均高于铸造件。通过改进铺粉装置,改善了成型设备的铺粉效果。(3)提出了免装配机构的数字化设计与选区激光熔化直接制造理念。通过引入间隙特征,建立了免装配机构的设计技巧,利用设计技巧优化了免装配机构的形状和结构,提高了其可加工性。分析选区激光熔化直接制造免装配机构的关键问题并提出了解决方法,包括:采用鼓形销和鼓形孔的形式优化间隙特征;通过装配角度的调整和摆放方式的合理选择改善机构的表面成型质量;采用倾斜摆放方式减少间隙特征的支撑数量;提高扫描速度以改善间隙特征的成型质量。通过若干机构样品的设计与直接制造,验证了免装配机构的数字化设计与直接制造方法是可行的。(4)研究了个性化零件的数字化设计。通过将个性化零件的结构元素分解为常规结构和个性化几何形状,提高了个性化零件的设计效率。在此基础上,提出了个性化托槽的组装式设计方法,采用结构特征组装的方式实现个性化托槽的快速设计。采用Typodont模拟矫治试验测试所设计和SLM直接制造的个性化托槽,结果表明,托槽能正确表达出预期的矫正力。(5)通过将复杂内腔零件的结构分解为基体结构和内腔结构,建立了复杂内腔零件的两个结构优化准则,即内腔结构中的粉末可以清除和内腔结构中的支撑不能影响功能实现。在此基础上,针对目前孔式喷嘴的冷却效果不明显和密封效果不好的缺点,基于SLM,对喷嘴结构进行了优化。更多还原

【Abstract】 Selective Laser Melting (SLM) is one of the major Rapid Prototyping (RP) technologiesthat can directly fabricate metal functional parts. SLM is the research focus and thedevelopment trend of RP since the SLM part is metallurgical bonded and has high relativedensity, high dimensional accuracy and good mechanical properties. The current research onSLM has been focused on material, process, equipment, application and fabrication of singlepart. The design of SLM part and the direct fabrication of mechanisms have been seldomstudied.Due to the research status, this paper investigates the digital design and direct fabricationof functional parts based on SLM. The main contents and results are as follows:(1) Freeform design of functional parts was studied. The design frame for functional partswas established, then the timing relationship between structure elements was analyzed. Theprinciple constraints of freeform design were studied, considering the aspects of laser deeppenetration, slic ing of model and focus diameter. The design guidelines for functional partswith freeform structure were proposed, which included the principle constraints and thegeneric freeform structures. Functional parts could be designed according to the genericfreeform structures, which had the advantages of nonstandard form of raw materials, nonetool feature, none fixture feature, freeform hole and freeform surface.(2) The expression of utilization rate of energy during SLM process and its correctionfactor were obtained according to the principle of themodynamics and the geometry ofpowder packing. Three types of overlapping mechanism, intra-layer overlapping mechanism,inter-layer overlapping mechanism and mix overlapping mechanism, were introducedaccording to the geometrical relationship between tracks under interlayer-staggered scanningstrategy. Some experiments have been carried out to study the relationships between scanningspace, scanning speed and relative density and to test the mechanical properties of parts.Result showed that the tensile strength and the yield strength of part by SLM werecomparable to the counterparts from casting. The powder laying device of the SLMequipment was also improved to obtain better powder laying effect.(3) A new concept was proposed that non-assembly mechanisms was digitally assembledand subsequently directly fabricated by SLM as assembled. After introduction of clearancefeature, the design skills for non-assembly mechanisms were proposed that the mechanismcomplexity could be reduced by reducing the part count and simplifying the part shape andthe processability could be improved by adjusting the clearance feature. The major factors in direct fabrication of non-assembly mechanism were studied and some solutions werepresented: (a) Using drum shaped pin and drum shaped hole to optimiz e the clearance feature;(b) Adjusting the assembly angle and display to improve the surface quality of mechanism; (c)Using tilting display to reduce the number of supports within the clearance feature; (d)Increasing scanning speed to improve the fabrication quality of clearance feature. Forexperimental verification, a number of mechanisms have been designed and directlyfabricated.(4) The digital design of customized parts was studied. The design efficiency wasimproved by classifying the structure elements of customized part as common structure andcustomized geometry. Then, a method was proposed to quickly design customized bracket,which was assembled using structure features. For experimental verification, a mouth ofcustomized brackets has been designed and directly fabricated by SLM, then been testedusing Typodont simulative experiment. Result showed that the brackets could express theexpected orthodontic force accurately.(5) Two design guidelines for optimization of parts with complicated cavity was proposedthat the powders within the cavity could be cleared and the supports within the cavity couldnot affect the performance by classifying the structure elements as base structure and cavitystructure. Then, the Hole coaxial nozzle has been optimized using the design guidelines basedon SLM since the current one had several defects such as unwell cooling effect and unwellseal.更多还原