InstRUmented Tool Holder for sensing metal cutting tool temperature and forces

 

Brandon Lane, Eric Whitenton, Vis Madhavan, and Alkan Donmez

 

 

To improve machining of complex products made of non-conventional and challenging materials, US manufacturers need smart machining tools that can sense, communicate, and provide feedback to reach optimized performance.  Common industry practice is to measure part conformity post-machining or to use low fidelity power monitoring to develop acceptable cutting conditions rather than sensing process characteristics in-situ.  This is even more common with high value-added parts such as those used in turbomachinery or aircraft structures.  Multiple cost- incurring performance characteristics such as tool wear, machining time, and part surface integrity have shown to relate to tool forces and temperature.  These, in turn, may be sensed using an instrumented tool holder (ITH) mounted with strain and temperature sensors. 

 

A prototype ITH was designed and fabricated from a 1” square grooving tool holder.  A thin-foil type strain gauge was mounted on holder in an area of high strain determined through finite element analysis.  In addition, a 0.010” diameter type-K thermocouple was mounted so that the carbide grooving inserts can easily be replaced between cutting tests.  This relatively inexpensive device was used to make ‘shop-grade’ measurements similar to what industry affiliates may use.  These measurements were then correlated to ‘laboratory-grade’ temperature and force measurements using a specially calibrated high speed thermal camera and 3-axis precision dynamometer.  The cutting tests were conducted on Ti-6Al-4V disks in a customized Edgetek grinding machine for a range of part speeds and depths of cut. 

 

Results of the first prototype ITH showed good correlation to the laboratory-grade force and temperature measurements, which in turn showed expected dependence on the input machining parameters.  The utility of the device was demonstrated to the NIST Smart Machining Consortium, a group of industry stakeholders that direct and provide feedback for NIST smart machining research, whose interest sparked the design of a second ITH prototype to be implemented in consortium member’s current manufacturing R&D endeavors.