A study of electromagnetic free forming in AA5052

The reduction of air pollution is currently a very critical issue. Presently, legislators are keen on coming up with policies to govern automotive sector, as road transport plays a fundamental role in air pollution with 16.4% of the global CO₂ emissions and 38% of the global oil consumption. Research has it that vehicles’ weight is directly proportional to the amount of fuel it consumes. As such, manufacturers have been forced to shift from steel-based vehicle parts towards the lighter aluminum parts. Unfortunately, the application of aluminum alloys has been limited by the fact that its formability is much lower than steel at room temperature.

Consequently, high strain rate forming techniques have been developed to improve the formability of aluminum, such as explosive forming, electro-hydraulic forming, electromagnetic forming. Electromagnetic forming is quite promising and has attracted wide attention due to its potential advantages. This process is usually too fast thereby making it difficult to observe by experimental means. As a result, the experimental data on the deformation history of electromagnetic forming is insufficient thereby necessitating further studies.

Recently, Hunan University scientists led by Professor Guangyao Li and Junjia Cui from the State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body investigated the deformation history (displacement, velocity, strain, strain rate) in the electromagnetic forming process. The team were keen to apply the digital image correlation technique to obtain the experimental data of deformation history. Their work is currently published in Journal of Manufacturing Processes.

The team considered AA5052 sheets electromagnetically free formed at various discharging energies with an elliptic spiral coil and an elliptical hollow die. Two high-speed cameras with a certain angle to each other were then used to photograph the entire deformation process. The DIC system was then used to calculate the full-field displacement, velocity, strain and strain rate. The sheets were then deformed into oval domes and the peak strain rate measured. Finally, a 3D numerical model was established using the method of combing Finite Analysis (FEA) and Boundary Element Method (BEM).

The authors found out that the FEA/BEM numerical model was valuable in studying the influence of deformation history on the dynamic behavior of materials. In addition, a comparison of results of metallographic and Vickers hardness confirmed that different strain histories affected material behaviors of formed parts. Specifically, the Vickers hardness results showed that the higher the peak strain rate the material experienced, harder the material became.

In summary, the study presented an in-depth assessment of the deformation process of 1.2 mm thick 5052 Aluminum alloy sheets measured using DIC technique. The general approach employed involved the establishment of a numerical model and the comparison of its results with those from the experimental procedure. Altogether, the simulation results were in good agreement with the experiments.