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 higher MQL level it was found a smaller tool wear.

However, the quality of the holes was similar for the both

lubrication levels tested.