【作者】 刘会霞；

【导师】 蔡兰；

【作者基本信息】 江苏大学 ， 机械制造及其自动化， 2011， 博士

【摘要】 随着微纳米科学与技术的不断发展,微小机电系统及其微结构器件的制作是近年来微制造研究的热点。微塑成形工艺因其在规模化批量生产方面的优势,在金属微结构的制作方面得到日益广泛的应用,已成为当前制造科学领域国内外学者研究学科前沿。本文在剖析国内外有关微塑成形技术,特别是激光冲击微成形技术研究的基础上,结合激光驱动飞片技术,提出了激光驱动飞片加载金属箔板间接冲击微成形的新方法。基于对激光驱动飞片加载方式及箔板成形机理的理论分析,开展激光驱动飞片间接冲击金属箔板的变形特性实验和有限元数值模拟研究。主要工作有以下几个方面：探讨了激光驱动飞片加载及其金属箔板成形的机理。包括激光诱导等离子体产生冲击波压力的数学模型、激光驱动飞片靶的结构及其影响因素、激光驱动飞片的解析过程、飞片高速碰撞靶材的冲击动力学行为、冲击波导致的温升和靶材高应变率的塑性变形,这些研究为微成形工艺参数的合理选取及成形过程的数值模拟奠定了基础。构建了激光驱动飞片加载下箔板间接冲击微成形的实验系统,初步揭示了激光间接冲击微成形能力与规律。通过对基于大面积阵列特征模具、单个圆孔模具和圆环模具的微成形实验,研究了激光能量、箔板厚度、离焦量对成形的影响,并对成形件的形貌和表面粗糙度的变化进行了分析,同时对典型成形件的应变分布进行了理论研究。研究发现：激光驱动飞片具有良好的加载功能,在合理的工艺参数下,可获得良好的成形效果,不但成形特征明显,而且成形表面质量好,可实现金属箔板的微成形要求；提高激光能量,可以增加成形深度,但是当激光能量大于某一特定值时成形件就会沿着模具边缘产生开裂现象,甚至是完全开裂,进一步研究发现激光驱动飞片加载技术也非常适合微冲裁工艺。基于ANSYS/LS-DYNA软件平台,采用显式动态分析模型,建立了激光间接冲击微成形的有限元分析模型,有效地解决了激光间接冲击微成形中载荷高、结构响应变化快的问题。模拟分析了激光间接冲击微成形中的瞬态响应过程、成形过程中的内能的变化、飞片加载后成形件的残余应力分布；研究了激光能量、微模具圆角半径和箔板与微模具的摩擦系数对于成形形貌和减薄率的影响。为成形工艺参数的优化和成形形状的预测和控制提供了手段。利用透射电子显微镜(TEM)对成形后的成形件微观组织演变情况进行了观察与分析。表明在飞片的高速加载作用下材料内部组织晶粒超细化,其达到纳米级别,在晶粒内部还存在一些纳米孪晶片层,其尺寸只有几个到十几纳米。提出了两种解释微成形过程中微观形貌的演化和晶粒细化机制：动态再结晶超细化和形变孪晶超细化机制。本文采用的激光驱动飞片的加载方式为材料超细晶的获取提供了一种新的途径。采用光滑粒子流体动力学方法(Smoothed Particle Hydrodynamics-SPH),以JohnSon-cook可拉伸积累损伤破坏模型为本构模型,对激光驱动飞片加载靶材产生层裂损伤现象进行了数值模拟研究,得到了靶材内部应力的变化规律以及飞片加载下靶材的层裂极值。研究成果为激光间接冲击微成形失效准则及控制提供参考和指导。更多还原

【Abstract】 With the continuous development of micro and nanotechnology, the manufacture of MEMS (Micro-Electro-Mechanism System) and its micro parts have become present research hotspot in micro manufacturing field. Because micro plastic forming technology has special advantages in large scale batch production, it has an increasingly extensive application on the manufacture of metallic microstructure. And it has already become the subject frontier of modern manufacturing field both at home and abroad. Based on the analysis of micro forming both at home and abroad, combining laser-driven flyer technology, a novel laser indirect shock micro forming is presented, which uses laser-driven flyer to load the sheet metal. Based on the theory analysis of the mechanism of laser-driven flyer and metal foil forming, a systematical study on the deformation property of metal foil indirect shock micro forming under laser-driven flyer were carried out from experiment and numerical simulation in this article. The main contents are as following:The mechanism of laser-driven flyer loading and metal foil forming were investigated, involving laser induced shockwave, shock force mathematical model, flyer target structures, influencing factors of laser-driven flyer, analytic representation of laser-driven flyer, impact dynamics of laser indirect shock forming, temperature rise of collision process and high strain rate plastic forming. This study laid a foundation for reasonable selection of the micro forming process parameters and numerical simulation of forming process.An experimental system for metal foil indirect shock micro forming under laser-driven flyer was developed. Through the research of micro forming based on micro channel networks mould, circular hole mould and circularity micro-channel mould, it analyses the effect of laser energy, workpiece thickness and defocusing on the deformation. The surface topography and roughness of the workpiece was investigated experimentally. And the theoretical strain distributions on typical formed parts were analyzed. It is found that the work piece has a high spatial resolution at the micron-level and the good surface quality is accomplished when process parameters are reasonable. The research results have shown the possibility of realizing sheet metal micro forming. The research on laser indirect shock micro forming showed that increasing the laser energy could increase the deformation depth, but may induce fracture when the laser energy is too high. Further studies proved that laser-driven flyer is also very suitable for micro punching technology.This paper also reports an investigation into laser indirect shock micro forming process through finite element simulation. ANSYS/LS-DYNA is an explicit dynamic analysis program, which is used to simulate the forming process. Comparing the simulated results with experiments, the precision and reliability are validated. The energy history, the displacement history and residual stresses field of the model are analyzed. The effect of laser energy, the die radius and the frictional coefficient on the deformation was numerically studied. The numerical simulation research provides means for optimization of process parameters, prediction and control of deformation shape.The microstructures of the treated samples were examined by transmission electron microscopy (TEM). The microstructures of the workpiece under laser-driven flyer loading are characterized by nano-sized grains and a small fraction of mechanical twins. And multiple mechanical twins appeared inside many grains. In the grain, twin boundaries are parallel to each other and they subdivide the grain into a thin twin-matrix (T-M) lamellar structure, of which the thickness varies from several to several tens of nanometers. The two structural refinement mechanisms are introduced: the dynamic recrystallization and the twin-matrix (T-M) lamellar refinement mechanism. Laser-driven flyer loading provides a new way for grain refinement.This paper uses the method of smoothed particle hydrodynamics and the model of Johnson-Cook tensile cumulative damage to simulate the spall induced by the laser-driven flyer loading. The change law of internal stress distribution and the extreme value of spall under laser-driven flyer are obtained. These results could offer some useful messages for the study on the failure criterion and controlling of laser indirect shock micro forming.更多还原