Direct measurement of lubricant film thickness during flat drawing process by fluorescence method

The lubrication state during plastic working is affected by the process conditions. It is known that changes in working speed and reduction of area cause changes in oil film thickness, and in situ observation is effective for quantitative evaluation. Therefore, the oil film thickness during flat drawing was measured by in situ observation using the fluorescence method. As the reduction of area increased, the oil film thickness in the parallel zone decreased, but the coefficient of friction decreased. This is thought to be due to the difference in lubrication conditions between the tapered zone (fluid lubrication) and the parallel zone (mixed lubrication) of the tool. Generally, as fluid lubrication has a lower coefficient of friction, the increase in the reduction rate leads to an expansion of the fluid lubrication region, which is considered to cause the decrease in the coefficient of friction.