Electromagnetic Forming of Aluminum Alloy Sheet Metal Utilizing a Low-Frequency Discharge: A New Method for Attractive Forming

In existing electromagnetic sheet metal forming processes, the sheet metal is typically deformed away from the coil under repulsive Lorentz forces. This deformation mode makes it difficult to apply the forming technology to dent repair without disassembly of the automobile body and aircraft fuselage. To solve this problem, a new electromagnetic attractive forming process with a low-frequency discharge current was developed in this work. Different from previous attractive forming methods, only a single coil and a single power supply are required that is low cost and easy to implement. Both numerical and experimental studies have demonstrated that an AA1060-H24 aluminum alloy sheet with a thickness of 1 mm can be effectively attracted towards the coil with a maximum deformation of more than 8 mm after a single discharge. More importantly, the mechanism of the attractive forming process has been clarified in detail through the analysis of the Lorentz force characteristics and deformation process of sheet metal. It has been pointed out that the current waveform after the first peak plays a vital role in improving the attractive force and the attractive forming process, which can be optimized by introducing a crowbar circuit. Meanwhile, it is found that the deformed shape of sheet metal caused by a repulsive force helps to facilitate the subsequent reverse deformation under an attractive force. This is also an important reason why an obvious attractive forming can be achieved, although the attractive force is much smaller than the repulsive force during the forming process. The obtained results have the significance for fundamental understanding of electromagnetic forming process, and further applications can be expected using the developed forming method.