汽车用铝合金焊件的点焊质量分析

发布时间：2018-07-06 18:15

本文选题：铝合金 + 点焊　；参考：《武汉工程大学》2015年硕士论文

【摘要】：铝合金具有密度小、强度高、良好的耐腐蚀性、易加工成型及资源丰富和可回收利用等优点,在航空航天、汽车制造、船舶及化学工业中已广泛应用。随着工业经济的飞速发展,对铝合金焊接结构件的需求日益增多,使铝合金的焊接研究也随之深入。电阻点焊是汽车制造厂在流水线上对整体式车身进行焊接时最长用的一种方法。而电阻点焊是集热、电、结构多物理场耦合的复杂过程,由于其焊接的瞬时性和不可见性,实验时,无法观测到整个熔核的形成过程;另外,铝合金具有易导电低电阻的特点,因此生成的焊点质量很差。铝合金电阻点焊数值模拟研究焊接机理是解决点焊问题的关键。本文以1.6mm厚的铝合金为对象,研究了铝合金电阻点焊的焊接机理。首先,基于有限元法,建立了电阻点焊的预压接触轴对称y有限元模型,确定热电瞬态分析时的初始导电区域;然后,运用序贯耦合法和热弹塑性理论全面分析了铝合金电阻点焊的热电瞬态机理和热弹塑性机理,通过对焊接区温度场分析,得到了熔核形状和尺寸。而在多点焊时,已焊焊点不可避免对在焊焊点存在分流现象,导致在焊焊点的热功率,降低焊接接头强度,本文通过对铝合金焊件在不同的点焊间距下进行数值模拟,发现随着点焊间距的增加,分流所占比例降低,熔核尺寸减小较慢,并以满足熔核焊透率为条件,得到在焊接电流为38KA,通电时间为0.166s时,1.6mm的铝合金工件最小点焊间距为17mm,这为点焊间距的选取提供理论依据。最后,通过对与上述数值模拟相同工艺参数的铝合金焊件进行静态拉剪试验,发现试样失效时多点焊的最大拉剪力与理论值相比有所衰减,且随着点距的减小,衰减的越快,从宏观上证明点焊分流对焊接接头强度的影响;将数值模拟得到的熔核截面形状与实验结果比较,两者基本一致,验证了数值模拟的正确性。
[Abstract]:Aluminum alloy has many advantages such as low density, high strength, good corrosion resistance, easy processing and forming, rich resources and recycling. It has been widely used in aerospace, automobile manufacturing, ship and chemical industry. With the rapid development of industrial economy, the demand for aluminum alloy welding structure is increasing day by day. Resistance spot welding is the longest method used by automobile factory to weld integral body on assembly line. The resistance spot welding is a complex process of collecting heat, electricity and structure with multiple physical field coupling. Because of its instantaneous and invisible welding, it is impossible to observe the forming process of the whole nugget in the experiment, in addition, the aluminum alloy has the characteristic of easy conducting and low resistance. The resulting solder joint is of poor quality. Numerical Simulation of Resistance spot Welding of Aluminum Alloy Welding Mechanism is the key to solve spot Welding problem. In this paper, the mechanism of resistance spot welding of 1.6mm thick aluminum alloy is studied. Firstly, based on the finite element method, the prepress contact axisymmetric y finite element model of resistance spot welding is established to determine the initial conduction region in transient analysis. The thermoelectric transient mechanism and thermoelastic-plastic mechanism of resistance spot welding of aluminum alloy were analyzed by using the sequential coupling method and thermoelastic-plastic theory. The shape and size of the nugget were obtained by analyzing the temperature field of the welding zone. However, in multi-spot welding, the phenomenon of shunt of welded joints is inevitable, which leads to the thermal power of welding joints and reduces the strength of welded joints. In this paper, the numerical simulation of aluminum alloy welds with different spot welding spacing is carried out. It is found that with the increase of spot welding distance, the proportion of flow decreases, the nugget size decreases slowly, and the penetration rate of nugget welding is satisfied. When the welding current is 38KAand the electric time is 0.166s, the minimum spot welding distance of 1.6 mm aluminum alloy workpiece is 17mm, which provides a theoretical basis for the selection of spot welding distance. Finally, through static tensile shear test of aluminum alloy welds with the same process parameters as the above numerical simulation, it is found that the maximum tensile shear force of multi-spot welding decreases compared with the theoretical value when the specimen fails, and the faster the attenuation is with the decrease of the distance between the points. The effect of spot welding flow on the strength of welded joints is proved from macroscopic view, and the numerical simulation results are compared with the experimental results, and the correctness of the numerical simulation is verified.
【学位授予单位】：武汉工程大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG453.9

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