Mechanical Study on the Effect of Initial Gap upon the Weldability of Various Spot Weld Joints

点焊过程可分为以下五个阶段。(1)从挤压开始到板材(工件)之间的初始接触；(2)由于挤压力的增加，工件之间的接触面积增大的过程。(3)恒压电流加热熔化过程。(4)保持挤压力的冷却过程。(5)释放挤压力用有限元方法分析了第一阶段和第二阶段的挤压过程，以阐明焊接接头几何形状和材料性能对闭合初始间隙和接触状态所需挤压力的影响。利用力学相似准则对所得结果进行了推广。基于推广的数据，提出了一种预测缩小初始间隙所需挤压力的方法。此外，还对第二阶段的精确接触状态进行了分析，并提出了一种确定允许初始间隙的方法。对于第二阶段之后的阶段，发展了轴对称热弹塑性问题的有限元求解方法，并推导了分析电流发热的数学公式。

The process of the spot welding can be divided into the following five stages. (1) from the beginning of the squeezing to the initial contact between plates (workpieces) (2) process in which the contact area between workpieces increases due to the increase of the squeezing force. (3) heating and melting process with the electric current with holding the squeezing force. (4) cooling process with holding the squeezing force. (5) releasing squeezing forceThe squeezing processes in the first and the second stages were analyzed by F.E.M. to clarify the effect of the weld joint geometry and material properties upon the squeezing force required to close the initial gap and the contact state. The obtained results were generalized using the mechanical similarity rules. Based on the generalized data, a methods to predict the squeezing force required to close the initial gap were proposed. Further, the precise contact state at the second stage was also analyzed and a method to determine the allowable initial gap was proposed. As for the stages after the second stage, Finite Element Method to solve the axisymmetric thermal-elastic- plastic problems was developed and the mathematical formulation to analyze the heat generation by the electric current were derived.