Measurement of the Beruforge 152DL thin-film lubricant using a developed thin-film thickness standard

Systematic deviations due to remaining lubricant on the workpiece have a significant influence on the measurement of sheet-hulk metal formed parts. The expected layer thickness for the workpieces after the forming process is less than 35 mu m. For the determination of the refractive index of the lubricant and thus the effects of the lubricant on optical measurement techniques, a lubricant thin-film thickness standard was developed which represents a continuous measuring range from 6 to 100 mu m. To determine the refractive index, the thin-film thickness standard was measured with a coaxial interferometric measurement system in various thickness ranges. Due to the knowledge of the optical and the geometrical path length, the refractive index can then be determined approximately. In addition, an XY stage was used to scan the entire thin-film area of the standard. The measurement setup in a temperature box allows for determining the effects of temperature changes on the optical properties of the lubricant.