【作者】 梁钰；

【导师】 陈培锋；

【作者基本信息】 华中科技大学 ， 物理电子学， 2009， 硕士

【摘要】 近年来,随着汽车与家电工业的迅速发展,人们对采用毛化技术轧制的冷轧薄钢板的深冲、涂镀性能的需求与日俱增。然而目前人们对激光毛化的研究还不是很充分,特别是对激光毛化工艺技术的研究距离生产实际的需求还有很大距离。因此,为了深入理解激光毛化的机理,进而优化加工参数,对激光毛化进行理论研究与数值仿真是很有必要的。本论文通过由浅入深建立理论模型并做相应的仿真分析的方式,对激光毛化的技术参数及其对激光毛化效果的影响进行了研究。本论文的主要工作如下:(1)从激光与材料相互作用时的热传导、熔质对流以及汽化作用等多个角度,详细阐述了激光毛化的机理,建立了激光毛化的数学模型。(2)以不考虑流体流动为基本假设,建立传统毛化光路系统的热传导模型,并进行了仿真研究,得出了扫描方式下只能得到形状不规则的椭圆形毛化坑的结论。(3)以改进光路为基础,在模型中考虑热传导过程中的相变潜热,通过有限元仿真展现了相变潜热的影响;得出激光功率和光斑半径分别与熔池宽度和深度近似呈线性关系,熔池中的最高温度近似与功率密度呈线性关系的结论,并初步确立了加工参数的大致范围。(4)建立了描述激光毛化的计算流体动力学模型,首先不考虑自由表面,只对自然对流做模拟,得出自然对流对熔池微形貌影响甚微的结论;然后对熔质表面张力梯度引起的Marangoni对流进行了模拟,并追踪了熔池自由表面的形成过程,得出毛化坑微形貌为中间凹陷、周围凸起的火山口状;并且得出在激光脉冲后半段,Marangoni对流的作用超过了热传导的结论,并进一步精选出了加工参数的范围。本论文的研究对激光毛化加工实践有一定的指导作用。更多还原

【Abstract】 In recent years, with the rapid development of automobile and electrical appliances industry, the need for the good stamping performance and fine brightness after painting of the cold-rolled sheet productions, which is rolled by the texturing technology, is growing faster day by day. However, the present studies on laser-texturing are not very sufficient, especially the studies on the craft technology of laser-texturing have a large distance from the demand of production practical. Therefore the theoretical study and numerical simulation is needed to help for understanding the physical mechanism of laser-texturing and choosing processing parameters.The theoretical models that from simple to complex are established and corresponding numerical simulation analysis is carried on in this thesis, and the laser-texturing processing parameters and their influence of texturing effect is studied to learn the laser-texturing technology. And this thesis concentrates these works such as followings:At first, the mechanism of laser-texturing is elaborated in detail by all these aspects such as the heat-conduction, convection of melt material, and vaporization during the laser-material interaction, and the mathematical model which is used for describing laser-texturing is established.Second, take the basic supposition that the fluid doesn’t flow, the heat-conduction model based on the traditional unimproved laser-texturing optics system, then the conclusion that it can only acquire ellipse and anomalous texturing-pit by the way of laser-scanning, through the corresponding simulation.Third, a model based on the improvement optics system, considering the phase-change latent heat during the heat-conduction process, and the influence of the latent heat is shown through Finite Element simulation. It gets a conclusion that the power of laser, and the radius of the laser facula has a approximate linearity relationship of the melt-pool’s width and depth respectively, and the simulation to this model also obtains a conclusion that the highest temperature in the melt-pool has a approximate linearity relationship of power-density. Then the scope of processing parameters is selected preliminarily.Fourth, based on the above works, the Computational Fluid Dynamics(CFD) model is established. At first the free-surface is unconsidered, and the function of free-convection is simulated, and it gets a conclusion that the free-convection has little influence on the microstructure of the melt-pool. Then, the function of Marangoni-convection, which is cause by the gradient of the surface tension, is simulated, and the free-surface’s formation- processing is traced, and the calculated microstructure of the texturing-pit is like a crater——there is a hollow in the middle, and the bulge surrounded the hollow. At last it gets a conclusion that the influence of Marangoni-convection may has bigger effect than the heat-conduction on the later time of laser-material interaction, then a more precise scope of processing parameter has been selected.This thesis have a certain instruction of the laser-texturing practical.更多还原