Diamond-Like-Carbon Coated Dies for Electromagnetic Embossing

Abstract

Electromagnetic forming is a high-speed process, which features contactless force transmission. Hence, punching operations can be realized with a one-sided die and without a mechanical punch. As the forces act as body forces in the part near the surface, the process is especially convenient for embossing microstructures on thin sheet metals. Nevertheless, the die design is critical concerning wear like adhesion. Several die materials were tested, like aluminum, copper as well as different steel types. For all die materials adhesion phenomena were observed. To prevent such adhesion an a-C:H-PVD (Physical Vapor Deposition)-coating was applied to steel dies (X153CrMoV12) and tested by embossing aluminum sheets (Al99.5). By this enhancement of the die adhesion was prevented. Furthermore, the die surface was structured with tribology-effective patterns that were generated by micro hard milling. The embossing quality was topographically analyzed with respect to different initial surface states of the sheets. It was identified that thicker sheets facilitate better embossing results. Moreover, the initial sheet surface has a decisive influence on the embossing quality, whereby the characteristic of the topography showed different susceptibility on the initial sheet surface state.

Electromagnetic Embossing of Optical Microstructures with High Aspect Ratios in Thin Aluminum Sheets

“…They identified further problems regarding significant die wear and sheet metal-die welding and concluded that die materials as well as coatings should be investigated to minimize these phenomena. Herrmann et al [17] examined DLC-coated dies for embossing of aluminum sheets and reduced the adhesion significant compared to dies out of aluminum, copper and two tool steels.…”

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

“…Heidhoff et al [4] replicated structures with retroreflective properties. Herrmann et al [5] demonstrated the replication of structures with tribological properties.…”

“…Risch et al [8] concluded that the high contact pressure in combination with the workpiece motion promote die wear in electromagnetic forming. Herrmann et al [5] showed that adhesive die wear in electromagnetic embossing can be reduced by DLC (diamond-like-carbon) coating. A higher amount of adhesion was observed when the die surface was prepared by polishing to receive a nearly optical surface roughness.…”