LUBRICATION LEVELS INFLUENCE ON CARBON FIBER-TITANIUM HYBRID STACKS DRILLING APPLYING MQL (MINIMUM QUANTITY LUBRICATION): PROCESS MONITORING

Abstract

The purpose of this paper is to analyze the influence of MQL (minimum quantity lubrication) lubrication level on hybrid stacks (Ti/CFRP/Ti) drilling process with diamond coated carbide tools. Spindle and feed motor power consumptions have been monitored which provides valuable information about the operation in real time which can be used to control and optimize the machining process and allows the implementation of 4.0 industry concepts. Furthermore, tool wear has been characterized and hole quality assessed. The tests were done with two lubrication levels with the same machining centers, tools, materials and cutting conditions as in the drilling processes of aeronautical components. With the fresh tool, the power consumptions were very similar for both MQL levels considered. Along the carbon fiber layers, the increase of cutting power with tool wear was higher for the test done with the lower MQL level. However, during Ti layers drilling, the increase of power was smaller for the lower MQL level, probably due to a higher titanium adhesion which modifies the chip formation process and a higher influence of the thermal softening effect on the workpiece. By using a reduced MQL level it was found a smaller tool wear. However, the quality of the holes was similar for the both lubrication levels tested. Keywords: MQL, hybrid stacks drilling, hole quality, tool wear, monitoring