Abstract
A loading force is very significant factor for the resistance spot welding. In a high-current density spot welding, the electromagnetic force increases proportionally to the square of muximum current in the reverse direction of loading, and as a consequence, it reduce the loading force. The fluctuation of the loading force in welding has direct effects upon the weldability. In this report, we investigate the influence of loading property on weldability and exibit the optimum laoding system in a high-current density spot welding. In a loading system with small spring constant, a nugget forms at the condition of the low current but the defect forms easaily at the interface, because an electrode moves in response to the electromagnetic force and the loading force is decreased in welding. In a loading system with large spring constant, it is difficalt to form the welded joint, because, the movement of an electrode is restrained and the loading force is increased by the thermal expansion. This trend is exposed remarkably for the material with a high thermal conductivity such as Al alloy. In a high-current density spot welding, it is very important to design the loading system under consideration of the electrode displacement by the electromagnetic force and thermal expansion.
