面向汽车轻量化的车身激光焊接热力学分析

发布时间：2018-03-27 22:10

本文选题：汽车轻量化　切入点：激光焊接　出处：《武汉理工大学》2015年硕士论文

【摘要】：汽车轻量化是汽车工业未来发展的主要趋势,也是解决能源消耗过快、减少环境污染的重要手段之一。车身重量占汽车总重量的40%左右,对实现汽车整体结构的轻量化有很重要的意义。使用先进材料和先进的连接方式是实现车身轻量化的重要途径。因此,在车身材质方面采用高强度钢或轻质合金代替传统钢板,同时在车身成形工艺方面采用激光焊接代替点焊、电弧焊等传统焊接方式引起了广泛关注。本论文的主要目的是研究车身新型材料先进高强钢以及轻质铝合金的激光焊接过程,采用有限元方法对焊接温度场和应力场的分布特点与变化规律进行仿真分析,并进一步讨论工艺参数对焊接结果的影响规律,从而为激光焊接的实际应用提供理论依据和参考。本论文的主要内容包括:(1)建立了车身典型焊接部位车顶与侧围的几何模型,利用Hyper Mesh软件建立有限元分析模型导入到ANSYS软件中进行有限元分析;对不同的热源模型进行讨论和总结,根据激光深熔焊匙孔形状和焊缝熔合线热点,提出了采用高斯面热源和峰值递增式圆柱体热源作为热源模型,并利用ANSYS特有的编程语言和生死单元技术实现了热源不规则移动、焊缝有序生成和循环加载过程。(2)对材料分别为BH钢和DP600高强钢的车顶与侧围激光焊接过程进行仿真模拟,研究了焊接熔池、温度场及热应力场的分布特点和变化规律,并分析了焊接工艺参数对熔池、温度场和热应力场的影响规律。结果表明:熔池尺寸和焊缝的最高温度随功率升高而增大,随焊接速度升高而减小;焊缝热应力随功率升高而减小,随焊接速度升高而增大。(3)对材料为轻质6061铝合金的车顶与侧围激光焊接过程进行仿真模拟,研究了焊接熔池、温度场及热应力场的分布和变化规律,并分析了铝合金焊缝温度场的变化规律,发现铝合金焊接温度场具有冷却快且热应力沿焊缝中心线两侧集中的特点。(4)搭建了激光焊接热历程测量系统,对激光焊接过程中不同位置的温度变化进行全程测量和记录。通过测量结果与模拟结果对比,验证了有限元模型和热源模型的可靠性,从而为激光焊接的工艺制定以及数值仿真提供了依据。
[Abstract]:Automobile lightweight is the main trend in the future development of automobile industry, and it is also one of the important means to solve the problem of excessive energy consumption and reduce environmental pollution. Body weight accounts for about 40% of the total vehicle weight. It is very important to realize the lightweight of the whole automobile structure. The use of advanced materials and the advanced connection mode is an important way to realize the lightweight of the body. Therefore, in the body material aspect, the high strength steel or light alloy is used instead of the traditional steel plate, At the same time, laser welding instead of spot welding, arc welding and other traditional welding methods have attracted wide attention. The main purpose of this paper is to study the laser welding process of advanced high-strength steel and light aluminum alloy. The distribution and variation of welding temperature field and stress field are simulated by finite element method, and the influence of process parameters on welding results is discussed. The main contents of this paper include: (1) the geometric model of roof and side circumference in typical welding position of car body is established. The finite element analysis model is established by Hyper Mesh software and imported into ANSYS software for finite element analysis. Different heat source models are discussed and summarized. According to the shape of keyhole and the hot spot of weld fusion line in laser deep fusion welding, different heat source models are discussed and summarized. The Gao Si surface heat source and the cylinder heat source with increasing peak value are used as the heat source model, and the irregular movement of the heat source is realized by using the special programming language of ANSYS and the technology of birth and death unit. The process of laser welding on the roof and side of BH steel and DP600 high strength steel was simulated. The distribution and variation of weld pool, temperature field and thermal stress field were studied. The influence of welding process parameters on weld pool, temperature field and thermal stress field is analyzed. The results show that the size of weld pool and the maximum temperature of weld increase with the increase of power and decrease with the increase of welding speed. The thermal stress of weld decreases with the increase of power and increases with the increase of welding speed. The laser welding process of roof and side of 6061 aluminum alloy with light weight is simulated and the weld pool is studied. The distribution and variation law of temperature field and thermal stress field, and the variation law of temperature field of aluminum alloy weld are analyzed. It is found that the welding temperature field of aluminum alloy has the characteristics of fast cooling and thermal stress concentration along both sides of the center line of the weld. The temperature changes in different positions during laser welding were measured and recorded. The reliability of the finite element model and the heat source model were verified by comparing the measured results with the simulation results. Therefore, it provides the basis for laser welding process formulation and numerical simulation.
【学位授予单位】：武汉理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG456.7

【参考文献】