Application of a combined heating system for the warm hydroforming of lightweight alloy tubes

A combined heating system – comprised of an induction coil plus a heating element – has been applied to the warm hydroforming of aluminum alloy tubes. For the rapid heating of tubes, a specially designed induction heating system has been developed as the main heating source. The induction heating system uses a high frequency induction coil in order to concentrate the energy into the tube and reduce energy losses. However, heat produced by the induction heating system was unequally distributed over the length and circumference of the tube, and as a result, the temperature distribution was non-uniform. An additional heating element was inserted into the inside of the tube to increase temperature uniformity by maintaining the forming temperature and reducing the heat lost to the tooling. Warm hydroforming tests with the combined heating system exhibit increased hydroformability, producing more uniform bulging in the tubes. The processing parameters such as internal pressure, axial feeding and heating conditions have also been successfully optimized.