Ultrasonic Reflection Technique for Measuring Contact Conditions at the Tool Chip Interface

SUMMARY

The measurement of the interface conditions in a cutting tool contact is essential information for performance monitoring and control. In this work, a new method for measurement of interface conditions, based on the reflection of ultrasound, is evaluated for use in turning in both dry and wet cutting conditions. An ultrasonic wave will be partially reflected when it strikes an interface between materials with different acoustic properties. The proportion of the wave reflected depends on the nature of the interface.
A transducer was positioned on the underside of a cutting tool insert and a pulse propagated through the insert. The pulse was reflected back at the tool-chip interface and received by the same transducer. The amplitude of the reflected wave was processed in the frequency domain. Reflection coefficient measurements were then used to investigate the tool-chip interface at different machining parameters including cutting speeds, depth of cut and feeds. It was seen clearly that the reflection coefficient increases with increasing cutting speed due to either a reduction in the tool-chip contact area or a decrease in the pressure applied on the rake face cutting tool. While the reflection coefficient decreases with increasing cutting depth and feed due to either an increase in the tool-chip contact area or an increase in the pressure. The results also showed that the reflection coefficient was significantly affected by feed followed by cutting speed whereas the depth of cut had the lowest effect on reflection coefficient. These results were attributed to the affect of tool-chip contact length with the machining parameters, where the depth of cut had the least effect on contact length.
When applying the cutting fluid, more energy was reflected back from the tool-chip interface and thus a higher reflection coefficient was recorded than in dry condition and this was due to the lower pressure that was applied on the rake face cutting tool.
The use of ultrasound in the monitoring of contact condition at the tool-chip interface is shown to be a viable technique for research and condition monitoring.