Abstract
In order to investigate the influence of characteristics of the power sources on the nugget formation under the various conditions of weld current and the electrode force which control the collapse of projection, the power sources with no-load voltage V20 of 3.3V and of 6.3V were used in this experiment.
When the power source with V20=3.3V was used under low electrode force where the projection was scarcely collapsed, for the weld current above a suitable value, the tensile shear strength was stable with small amount of scatter and the welds failed in tear fracture in spite of occurrence of the initial splash during collapse of projection and the splash in the latter half weld time.
However, when the power source with V20=6.3V was used, the tensile shear strength was unstable with a large amount of scatter and the welds failed in the shear or the tear fracture at the rate about 50 % because of the initial intensive splash, so that the critical current could not be defined. Thus, the drooping characteristics with high no-load voltage were found to be able to supply the initial heat input into the projection part more than those with low no-load voltage.
However, under low electrode force the enlargement of the area of the current path due to the initial extensive splash decreased the current density and the heat efficiency, and after that these deep drooping characteristics were found to be unable to the following heat input enough to conpensate for this heat loss.
Under high electrode force where the projection was almost collapsed, the critical current was defined even if the power source with different no-load voltages were used. And the value of critical current in the case of using the power source with V20=6.3V was found to be 1000A smaller than that of the power source with V20=3.3V.
