Influence of cooling lubricants on mechanical load at the cutting wedge using high-speed microcinematography and an open-contra rotation tribometer

Abstract

The use of cooling lubricant (CL) in machining influences the thermo-mechanical load of the tool and can increase both the workpiece quality and the metal removal rate. However, a targeted design of the CL supply strategy is not possible due to a lack of basic knowledge on the mechanisms of cooling lubricants. Therefore, the mechanical load on the cutting wedge is investigated in dependence of the CL-supply pressure for a cutting oil and an emulsion. It can be seen that the maximum normal stress increases with increasing CL-pressure due to a reduction in contact length. The maximum tangential stress shows a minimum for p = 45 bar and therefore a reduction in mechanical tool load when using cooling lubricants. The friction in the secondary shear zone is analysed using local coefficients of friction and an open contra-rotation tribometer. A critical contact length CL_RF,crit has been determined where a significant reduction in friction as a result of the lubrication of the chip-tool contact occurs for an increasing contact at the rake face. In order to investigate the contact conditions in the presence of CL fundamental tribometer investigations were conducted. Based on this it is shown that there is no penetration to the cutting edge near the primary shear zone using CL-supply from the rake face.