西 南 交 通 大 学
本科毕业设计（论文）
中英文摘要
年 级: 2011级
学 号: 20111337
姓 名: 赵智堂
专 业: 热能与动力工程
指导老师: 卢耀辉
2015年6 月
摘 要
焊接结构具有生产率高、便于自动化、工作环境好等优点，因而被广泛应用到工程生产领域的各个方面。由于焊接是一个局部受热温度急剧升高，然后逐步冷却的过程，在焊接过程中还伴随着相变，因此焊接结构会引起较大的焊接变形和焊接残余应力。其中，过大的焊接变形会影响焊接件的外观、表面质量和装配精度，而焊接残余应力则会影响焊接件的各种强度指标，引起热裂纹、冷裂纹等结构缺陷，严重的情况下，会使得零件的稳定性下降，从而导致结构的静载能力下降。对上述缺陷的校正会花费大量的人力物力，造成零件成本攀升。因此，在焊接过程中，充分了解焊接的基本规律、对焊接结构焊接变形进行预测、焊接方式进行优化、对于实际生产过程有很重要的意义。由于焊接结构的复杂性，焊接变形预测在实际操作中比较困难，目前主要有数值计算和实验预测两种方法，实验预测对于大型焊接件应用并不经济，随着计算机的发展，数值计算方法得到越来越多的应用。
本文采用热弹塑性有限元理论，利用ANSYS 软件对铝合金焊接常见的对接和角接接头进行数值模拟，并得出相应的结论。首先，将实际的焊接模型分为若干部分，在preo 中以组件的方式建立各个部分的模型再组装成一个整体；然后将建好的模型导入ANSYS ，在定义材料参数之后将模型离散化，为了保证网格的质量，采用先在面上生成网格，在扫略到体上的方法，在焊缝处网格的尺寸为2mm ，远离焊缝的区域为3mm ；在划分完网格之后，进行温度场的计算，为了实现焊接热源的移动效果，需要使用生死单元技术，具体做法是：将焊缝所在的体在焊缝方向上等分为等分若干个体，在焊接之前将体上的所有单元都杀死，在焊接过程中依次激活，随着热源的移动，热量以内部生热率的方式加载到每一个等分的体上，在计算下一个体的温度场是，将上一个体的生热率删除，同时将上一个体的结果作为该体的初始条件；最后计算焊接残余应力和焊接变形，在计算过程中首先在相应的线上施加约束，然后添加所需的材料参数，最后江温度场计算结果读入计算焊接残余应力和焊接变形。在计算温度场和应力场时，都是由相应的命令流完成，此外，为了使结果收敛更快，要采用牛顿-拉普森法进行迭代，同时激活自适应下降功能，打开大变形和自动时间步长预测。
通过计算结果可以得出以下结论：采用热弹塑性有限元法能够实现焊接过程的再现。由温度场结果可以发现，对接接头模型焊接温度最高可以达到1600℃，温度场具有明显的对称性，在冷却过程温度场呈波浪形扩散；角接接头焊接最高焊接温度可以达到1400℃，温
第1页
度场没有明显的对称性，在冷却过程中温度场扩散也没有明显的规律。对比两者可以发现，铝合金散热能力强，冷却很快，温度变化较为剧烈。由焊接残余应力的计算结果发现，对于两种接头，在焊缝处都会形成较大的拉应力，使得焊接件容易在焊缝处发生应力开裂；角接接头在焊接之后或形成较大的拉应力区域，将会对焊接件的承载能力造成不利影响。由焊接变形计算结果发现，对于两种接头，焊接变形都是由起弧端开始逐渐增大，在焊缝中点附近达到最大值，之后逐渐减小，收弧端的焊接变形要大于起弧端，经过对比，角接接头焊缝处的焊接变形明显比对接接头小；在对接接头中，焊缝左侧的焊接变形明显小于焊缝右侧，说明在焊接过程中可以用夹具对焊接件进行固定以减小焊接变形。
关键词：铝合金焊接，焊接接头，焊接温度场，焊接残余应力和焊接变形，有限元
Abstract
Student ：ZHAO zhi-tang,Teacher:LU yao-hui
(Dept.of Thermal Energy and Power Engineering,2011)
第2页
Welded structure with high productivity, easy to good automation, work environment, etc., which are widely applied to all aspects of production in the field of engineering. Because welding is a sharp increase in local heating temperature, and then gradually cooling process, the welding process is accompanied by a phase change, it will cause a large welded structure welding deformation and welding residual stress. Which is too large welding deformation will affect the appearance, surface quality and assembly precision weldments, and welding residual stress can affect a variety of strength index weldments, causing structural defects hot cracking, cold cracking, etc., in severe cases, decreased stability will make the parts, resulting in static load capacity of the structure decreases. Correction of the defect will spend a lot of manpower and resources, resulting in rising component costs. Thus, in the welding process, welding fully understand the basic laws of the welded structure welding deformation prediction, welding is optimized for the actual production process has very important significance. Because of the complexity, welding deformation prediction in the actual operation of welded structures is difficult, there are mainly two kinds of numerical prediction and experimental methods, experimental prediction for large welded applications are not economic, with the development of computer numerical methods more and more applications.
In this paper, using thermal elastic plastic finite element theory, the use of ANSYS software, the common butt welding of aluminum corner joints and numerical simulation, and draw the appropriate conclusions. First, the actual welding model is divided into several parts, in preo by way of the component parts of each model and then assembled into a whole; and built a good model into ANSYS, after defining discrete material model parameters, in order to ensure the quality of the grid, using the first in the region to generate the mesh surface, in the process of sweeping onto the body, in the weld mesh size of 2mm, away from the weld to 3mm; after the division completed the grid, calculate the temperature field in order to achieve the effect of welding heat source movement, the need to use the death cell technology, which would be: the weld seam is located in the direction of the upper body is divided into a number of individual aliquots before welding on the body All units are killed in order to activate the welding process, with the heat source movement, heat to internal heat generation rate loadable into an aliquot of each body, in the calculation of the temperature field next individual that will last Remove body
第3页
heat rate, while a member of the result as an initial condition of the body; the final calculation of welding residual stress and distortion, first applied in the calculation process constraints in the corresponding line, then add the required material parameters Finally, the river temperature field calculation results read into the welding residual stresses and weld distortion. In calculating the temperature field and the stress field is completed by the corresponding order flow, in addition, in order to make the results faster convergence to Newton - Raphson iteration method, while activating the adaptive decline in function, open the large deformation and automatic forecast time step.
By calculating the results the following conclusions: using thermal elastic plastic finite element method enables the reproduction of the welding process. The temperature field results can be found, the highest butt joint welding temperature model can reach 1600 ℃, the temperature field has obvious symmetry, wavy diffusion temperature field during cooling; fillet weld joint welding highest temperature can reach 1400 ℃, temperature field no obvious symmetry, temperature field during cooling diffusion no obvious pattern. Compare the two can be found aluminum cooling capacity, cooling quickly, more severe temperature changes. From the results of welding residual stress was found two joints in the weld will form a large tensile stress, making weldments susceptible to stress cracking in the weld; corner joints after soldering or form larger pull stress areas will adversely affect the carrying capacity of the weldment. The results found by the welding deformation, for both joints, welding deformation is the beginning of the end of arcing increases, reaches a maximum near the midpoint of the weld, and then gradually decreased, welding deformation crater end is greater than the arc end After comparison, fillet weld joints of welding deformation is significantly smaller than the butt joints; butt joints in welding deformation of the weld seam on the left side is significantly smaller than the right side, indicating that the welding process can be carried out with a jig of weldment Fixed to reduce welding deformation.
Keywords ：Aluminum welding，Welded joints，Welding temperature field，Welding residual stress and the welding deformation，Finite element
第4页
西 南 交 通 大 学
本科毕业设计（论文）
中英文摘要
年 级: 2011级
学 号: 20111337
姓 名: 赵智堂
专 业: 热能与动力工程
指导老师: 卢耀辉
2015年6 月
摘 要
焊接结构具有生产率高、便于自动化、工作环境好等优点，因而被广泛应用到工程生产领域的各个方面。由于焊接是一个局部受热温度急剧升高，然后逐步冷却的过程，在焊接过程中还伴随着相变，因此焊接结构会引起较大的焊接变形和焊接残余应力。其中，过大的焊接变形会影响焊接件的外观、表面质量和装配精度，而焊接残余应力则会影响焊接件的各种强度指标，引起热裂纹、冷裂纹等结构缺陷，严重的情况下，会使得零件的稳定性下降，从而导致结构的静载能力下降。对上述缺陷的校正会花费大量的人力物力，造成零件成本攀升。因此，在焊接过程中，充分了解焊接的基本规律、对焊接结构焊接变形进行预测、焊接方式进行优化、对于实际生产过程有很重要的意义。由于焊接结构的复杂性，焊接变形预测在实际操作中比较困难，目前主要有数值计算和实验预测两种方法，实验预测对于大型焊接件应用并不经济，随着计算机的发展，数值计算方法得到越来越多的应用。
本文采用热弹塑性有限元理论，利用ANSYS 软件对铝合金焊接常见的对接和角接接头进行数值模拟，并得出相应的结论。首先，将实际的焊接模型分为若干部分，在preo 中以组件的方式建立各个部分的模型再组装成一个整体；然后将建好的模型导入ANSYS ，在定义材料参数之后将模型离散化，为了保证网格的质量，采用先在面上生成网格，在扫略到体上的方法，在焊缝处网格的尺寸为2mm ，远离焊缝的区域为3mm ；在划分完网格之后，进行温度场的计算，为了实现焊接热源的移动效果，需要使用生死单元技术，具体做法是：将焊缝所在的体在焊缝方向上等分为等分若干个体，在焊接之前将体上的所有单元都杀死，在焊接过程中依次激活，随着热源的移动，热量以内部生热率的方式加载到每一个等分的体上，在计算下一个体的温度场是，将上一个体的生热率删除，同时将上一个体的结果作为该体的初始条件；最后计算焊接残余应力和焊接变形，在计算过程中首先在相应的线上施加约束，然后添加所需的材料参数，最后江温度场计算结果读入计算焊接残余应力和焊接变形。在计算温度场和应力场时，都是由相应的命令流完成，此外，为了使结果收敛更快，要采用牛顿-拉普森法进行迭代，同时激活自适应下降功能，打开大变形和自动时间步长预测。
通过计算结果可以得出以下结论：采用热弹塑性有限元法能够实现焊接过程的再现。由温度场结果可以发现，对接接头模型焊接温度最高可以达到1600℃，温度场具有明显的对称性，在冷却过程温度场呈波浪形扩散；角接接头焊接最高焊接温度可以达到1400℃，温
第1页
度场没有明显的对称性，在冷却过程中温度场扩散也没有明显的规律。对比两者可以发现，铝合金散热能力强，冷却很快，温度变化较为剧烈。由焊接残余应力的计算结果发现，对于两种接头，在焊缝处都会形成较大的拉应力，使得焊接件容易在焊缝处发生应力开裂；角接接头在焊接之后或形成较大的拉应力区域，将会对焊接件的承载能力造成不利影响。由焊接变形计算结果发现，对于两种接头，焊接变形都是由起弧端开始逐渐增大，在焊缝中点附近达到最大值，之后逐渐减小，收弧端的焊接变形要大于起弧端，经过对比，角接接头焊缝处的焊接变形明显比对接接头小；在对接接头中，焊缝左侧的焊接变形明显小于焊缝右侧，说明在焊接过程中可以用夹具对焊接件进行固定以减小焊接变形。
关键词：铝合金焊接，焊接接头，焊接温度场，焊接残余应力和焊接变形，有限元
Abstract
Student ：ZHAO zhi-tang,Teacher:LU yao-hui
(Dept.of Thermal Energy and Power Engineering,2011)
第2页
Welded structure with high productivity, easy to good automation, work environment, etc., which are widely applied to all aspects of production in the field of engineering. Because welding is a sharp increase in local heating temperature, and then gradually cooling process, the welding process is accompanied by a phase change, it will cause a large welded structure welding deformation and welding residual stress. Which is too large welding deformation will affect the appearance, surface quality and assembly precision weldments, and welding residual stress can affect a variety of strength index weldments, causing structural defects hot cracking, cold cracking, etc., in severe cases, decreased stability will make the parts, resulting in static load capacity of the structure decreases. Correction of the defect will spend a lot of manpower and resources, resulting in rising component costs. Thus, in the welding process, welding fully understand the basic laws of the welded structure welding deformation prediction, welding is optimized for the actual production process has very important significance. Because of the complexity, welding deformation prediction in the actual operation of welded structures is difficult, there are mainly two kinds of numerical prediction and experimental methods, experimental prediction for large welded applications are not economic, with the development of computer numerical methods more and more applications.
In this paper, using thermal elastic plastic finite element theory, the use of ANSYS software, the common butt welding of aluminum corner joints and numerical simulation, and draw the appropriate conclusions. First, the actual welding model is divided into several parts, in preo by way of the component parts of each model and then assembled into a whole; and built a good model into ANSYS, after defining discrete material model parameters, in order to ensure the quality of the grid, using the first in the region to generate the mesh surface, in the process of sweeping onto the body, in the weld mesh size of 2mm, away from the weld to 3mm; after the division completed the grid, calculate the temperature field in order to achieve the effect of welding heat source movement, the need to use the death cell technology, which would be: the weld seam is located in the direction of the upper body is divided into a number of individual aliquots before welding on the body All units are killed in order to activate the welding process, with the heat source movement, heat to internal heat generation rate loadable into an aliquot of each body, in the calculation of the temperature field next individual that will last Remove body
第3页
heat rate, while a member of the result as an initial condition of the body; the final calculation of welding residual stress and distortion, first applied in the calculation process constraints in the corresponding line, then add the required material parameters Finally, the river temperature field calculation results read into the welding residual stresses and weld distortion. In calculating the temperature field and the stress field is completed by the corresponding order flow, in addition, in order to make the results faster convergence to Newton - Raphson iteration method, while activating the adaptive decline in function, open the large deformation and automatic forecast time step.
By calculating the results the following conclusions: using thermal elastic plastic finite element method enables the reproduction of the welding process. The temperature field results can be found, the highest butt joint welding temperature model can reach 1600 ℃, the temperature field has obvious symmetry, wavy diffusion temperature field during cooling; fillet weld joint welding highest temperature can reach 1400 ℃, temperature field no obvious symmetry, temperature field during cooling diffusion no obvious pattern. Compare the two can be found aluminum cooling capacity, cooling quickly, more severe temperature changes. From the results of welding residual stress was found two joints in the weld will form a large tensile stress, making weldments susceptible to stress cracking in the weld; corner joints after soldering or form larger pull stress areas will adversely affect the carrying capacity of the weldment. The results found by the welding deformation, for both joints, welding deformation is the beginning of the end of arcing increases, reaches a maximum near the midpoint of the weld, and then gradually decreased, welding deformation crater end is greater than the arc end After comparison, fillet weld joints of welding deformation is significantly smaller than the butt joints; butt joints in welding deformation of the weld seam on the left side is significantly smaller than the right side, indicating that the welding process can be carried out with a jig of weldment Fixed to reduce welding deformation.
Keywords ：Aluminum welding，Welded joints，Welding temperature field，Welding residual stress and the welding deformation，Finite element
第4页