Impact of Die Coatings on Forming Conditions in Electromagnetic Embossing of Thin Sheet Metal

Abstract

In electromagnetic embossing, the interaction of the magnetic field and the induced current density results in body forces that enable the replication of optical microstructures into thin sheet metals. However, as the sheet metal is completely penetrated by the magnetic field, electromagnetic properties of the dies need to be considered in process design, as they influence the forming conditions by changing the field distribution, force vectors and eddy current densities. With die coatings like electroless nickel–phosphorus (NiP), the electromagnetic properties of the die change. Therefore, the effect of both - die substrate and coating material - was studied to find advantageous conditions for electromagnetic embossing. Within two-dimensional electromagnetic field simulation, the electromagnetic properties of coating and substrate material were varied in addition to the coating thickness. To validate the results, electromagnetic embossing experiments were carried out. Here, different dies were fabricated from aluminum (uncoated) and cold work steel with 200 µm and 400 µm thick electroless nickel–phosphorus coatings that were subsequently micro-structured in optical surface quality. It was demonstrated by numerical and experimental results that the coating and the substrate influence the electromagnetic embossing significantly in correspondence to their shielding behavior and field interaction due to electromagnetic properties and coating thickness.