| Resistance spot welding plays an important role in the automobile manufacturing industry,and its joint connection quality seriously affects the safety of automobiles.Nowadays,the proposal of lightweight body makes more and more use of corrosion-resistant metal,light alloy and high-strength steel on the body,which puts forward higher requirements on the resistance spot welding process.When ordinary electrode welding,the energy is concentrated in the center area of the solder joint,resulting in energy concentration,which is prone to defects such as welding spatter and excessive indentation.In order to better adapt to the spot welding connection of new metal materials,this experiment uses a new type of composite ring end electrode,referred to as ring electrode.On the basis of ordinary electrodes,ceramic rods are embedded in the end faces of the electrodes,so as to use the non-conductivity of ceramics to control the current flow path and reduce the energy density in the central area.This subject researches the spot welding connection of galvanized steel sheet,DP980 homogenous metal and steel/aluminum dissimilar metal under the composite ring end electrode.It not only guides the connection of new metals on the lightweight car body,but also optimizes the electrode and resistance spot welding.The development of connection technology provides theoretical guidance and has important practical significance.First,a ring electrode is used to carry out resistance spot welding tests on 1.0mm thick galvanized steel sheets to explore the surface morphology,indentation depth,nugget diameter and melting of the spot welded joints under different welding parameters(welding current,welding time and electrode pressure).The cross-sectional morphology of the core is used to study the influence of welding parameters under the ring electrode on the nugget shape and mechanical properties of spot welded joints of different metal materials.The research results show that in the spot welding test of galvanized steel sheet,the ring electrode has a significant effect on controlling the energy distribution and changed the growth mode of the nugget.Under the ordinary electrode,the nugget is first generated in the center area of the solder joint,and as the heat input increases,the nugget grows around.The nugget under the ring electrode first generates a ring-shaped nugget at the solder joint,and with the increase of heat input,the ringshaped nugget grows to both the inner and outer sides at the same time,which can increase the diameter of the nugget to a certain extent.Using the ring electrode's ability to control energy distribution,experiments were carried out on the spot welding connection of steel/aluminum dissimilar metals.The research results show that although the ring electrode can show the ability to control the energy distribution on the surface of the workpiece,the thermophysical properties and chemical metallurgical properties of steel(galvanized steel)and aluminum(Al5754)are very different,making the ring electrode on the workpiece-The energy distribution is not well controlled during the growth process of the nugget between the contact surfaces of the workpieces,and the fracture forms of the steel/aluminum spot welded joints are all shown as interface fractures when the mechanical properties of the steel/aluminum spot welded joints are tested.The resistance spot welding test of DP980 was carried out with a combined electrode.Due to the combination of a common electrode and a ring electrode,it can be seen from the distribution of the nugget that the ring electrode's ability to control energy distribution is weakened and the nugget shift has occurred.Phenomenon,so that the nugget is biased to the side of the ring electrode.Using the characteristics of the ring electrode,when welding unequal thickness plates,the ring electrode can be used on the side of the thin plate to reduce the deviation of the nugget.In addition,during the mechanical performance test,the pull-out fracture of the joint is mostly manifested as the nugget on the side of the ordinary electrode is pulled out,which further shows the ability of the ring electrode to reduce the temperature in the center area of the solder joint and increase the size of the nugget.In addition to experiments,a numerical simulation finite element model of DP980 spot welding was also established.Through the combination of experiment and simulation,the forming process of the nugget was further studied. |
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