Study On Dynamic Characteristics To Nugget Forming Process In Resistance Spot Welding Of Aluminum Alloy

Resistance spot welding is accompanied by various forms of energy release such as electricity,sound,heat,etc,which have a close relation with nugget forming process.In this paper,the electrode voltage,welding current and structure-borne acoustic emission（AE）in the welding process are detected in real-time.Based on these informations,the nugget nucleation and growth,quality identification,the influence of spatter and electrode loss on the nugget growth,including the impact of TiO₂ powder,are analyzed.In addition,the numerical model is established by ANSYS,the heat transfer and electric potential in nugget growing process are studied.The results showed that,the process of nugget forming can be divided into three stages according to the dynamic resistance curve,including primary stage,growth stage and stable stage.The nugget shows diverse nucleation characteristics in different stages.With the affection of different energy input,the dynamic process of nugget forming was presented in dynamic resistance curves.The characteristic parameters of electrical signals are related with nugget size and bearing capacity of the spot weld,which provides a basis for the identification of nugget quality according to the real-time detection of nugget dynamic signals.According to the analysis of dynamic resistance and AE signals,it is found that the spatter often occurs in the middle and late stage of the nugget stabilization.With the electrode loss increased,the variation of dynamic resistance is significant and the nugget quality is affected.This technology can be used to evaluate the degree of electrode loss in the process of resistance spot welding,which provides a theoretical basis for real-time monitoring of electrode loss.The TiO₂ powder has changed the contact state of workpiece,which improving the dynamic resistance of initial stage of nucleation.Larger nugget size and stronger bearing capacity of spot weld are realized by the affection of TiO₂ powder.By ANSYS calculation,it is found that the temperature is varied with the nucleation growth process and welding process.TiO₂ powder can improve the electrode voltage,thereby improve the contact and dynamic resistance.So the nucleation thermal effect is increased,which improves the nugget diameter and raises the bearing capacity of spot weld.