Abstract
Production of additively manufactured sandwich sheets is limited to small sizes. In the newly introduced process route, additively manufactured core structures are joined with large rolled face sheets by resistance welding, and the formability of the hybrid sandwich sheets is investigated. The necessity of developing the humps to improve the quality of resistance welding is initially investigated. Two different core structures, namely honeycomb and hollow sphere, are selected, and electrical-thermal coupled simulations with the abaqus software are performed to study the temperature distribution during resistance welding without and with hump. The strength of the joints for the fabricated sandwich sheets is verified by a quasi-static shear test. It is experimentally proven that the sandwich sheets without a hump in the core structure are not fully joined, and desired temperature localization is possible only by applying the hump. This is because the hump reduces the contact area, which leads to an increase in current density at the point where the resistance ratios are changed. This leads to higher temperatures in the intended joining zone. Different hump geometries for the core structure are designed, fabricated, and joined to the face sheets under different process parameters. The spot contact yields up to 50% higher shear strength than the linear or area contact. The free air-bending results show that the double weld is essential for successful subsequent bending. It is also concluded that increasing the resistance welding time by more than 120 ms does not affect the joining strength of hybrid sheets.
