How dry is dry? - A critical analysis of surface conditions used in dry metal forming

In the present study, the surface conditions of workpieces used for dry-metal forming experiments were analyzed. Specifically, the effectiveness of different cleaning approaches was evaluated using x-ray photoelectron spectroscopy, infrared spectroscopy and wetting experiments. The best cleaning results were obtained using a CO2-based approach. CO2 acts as an effective solvent and as a result of the mechanical impact, it removes material from the surface. In fact, cleaning results were similar to those achieved by plasma cleaning. However, even simple cleaning with a towel and acetone left only a surface film of less than 100 nm. A residual oil film thickness below 100 nm on the work piece appears sufficient to mimic true dry-forming conditions in most cases. In order to determine cleanliness of surfaces used in dry-metal forming, an infrared spectroscopy-based oil film gauge along with a customized extended calibration curve turned out to provide for sufficiently accurate data.