Research On Nucleation Mechanism And Technology Of Resistance Spot Welding With Medium

Spot welding is widely applied to the welding of sheet. It is an major method in modern automobile manufacture industries, it has been widely used in sheet-metal joining for auto-body because the advantage and efficient robotization.Spot welding with medium means joining medium between the workpiece for spot welding. In this paper, based on the experimental materials to aluminum and electric paste that is a mixture of electric materials and aluminium powder for spot welding experiment, the shape, defect and structure of LF21 rust-resisting aluminum weld nugget both with medium and without medium have been studied by metallographic analysis.. The results show that all of the spot nuggets without using medium appear gas cavities and lack of fusion, while those using medium appear well. There is only few little gas cavity, but no lack of fusion which does more damage to mechanical of nugget in the latter situation. Furthermore, the requirement on the surface of aluminum alloy workpiece is reduced, thus avoiding the treatment of workpiece surface. Resultingly, the quality of aluminum alloy nugget can be guaranteed easily. The welding current can be reduced. That guaranteed lower electrode temperature and enhances the electrode life.The instantaneity of spot welding with medium process make it difficult to experiment research of the nugget growth process and it is unbelievable to only numerical simulation. So,the numerical simulation is implemented to investigate the process mechanism of aluminum alloy resistance spot welding with meduim in this thesis. According to elastoplastic and contact theory,an axial symmetry finite element model of pre-squeeze contact analysis for aluminum alloy RSW with cone-shaped electrode is developed. The contact behaviors in pre-squeeze stage of aluminum alloy RSW are simulated and the initialized regional contacts is decided by this model. According to the basic equation of depicting resistance spot welding with meduim process, an axial symmetric finite element model of thermal and electrical coupled analysis for the process of aluminum alloy resistance spot welding with meduim is developed in this thesis based on the finite element theory. In this model,the thermal physical properties,the latent heat of phase change are considered. Simulation results show that the smaller the current(13KA) can be quite satisfactory the full shape of the nugget.In short, under the conditions of accession to medium, experimental and simulation results showed that significantly reduced the welding current, improving the welding spot welding technology; improving the electrode life.