Design and Evaluation of a Piezoelectric Actuator for Turning
            Albert A. Espinoza, Dept. of Mechanical Eng., University of Texas at Austin
            Luke J. Mayer, Dept. of Mechanical Eng., Texas Tech University
            Paul V. Oberlin, Dept. of Mechanical Eng., Texas A & M University
Matthew Bement, Weapons Response Group, Los Alamos National Laboratory

The machining process of turning is very important for many manufacturing applications.  In high precision machining applications, in particular, the surface finish of turned parts is a major concern.  Surface finish is strongly correlated with vibrations and dynamic interactions between the part and the cutting tool.  Process characteristics such as: spindle speeds, cut depths, feed rates, and part material properties, can vary in real-time and have unexpected and undesirable effects on these vibrations and dynamic interactions.  Thus, it is desirable to have a high bandwidth actuator capable of allowing a control system to react to these changing vibration conditions, resulting in an improved surface finish.  Consequently, this research project focuses on the fabrication and on the analytical and experimental performance testing of a high bandwidth, high force, low displacement piezoelectric actuator for use between the tool and the tool holder.  The dynamic characteristics of the actuator are analyzed by performing a finite element model.  Next, the baseline performance of the actuator is characterized experimentally in non-cutting condition environments, using tools such as accelerometers and non-contact laser vibrometers.  Furthermore, the self-sensing capability of the actuator is measured.  Finally, the cutting condition performance of the actuator is evaluated in face cutting operations on aluminum, and its effects on surface finish are measured using non-contact profilometry.  Based on the results from these experiments, the performance characteristics of the actuator are documented for future use in high precision machining operations.


 

Project Description and Approach
This project focuses on the machining process of turning. A high bandwidth
piezoelectric actuator will be designed for studying the effects such an actuator can have
on surface finish as well as on process stability behaviors such as chatter characteristics.
It is intended that the design and evaluation of this actuator will expose project
participants to a variety of concepts and techniques that are important in a modern, agile
manufacturing environment, including model based design, in process monitoring, non contact
metrology and advanced process control.
The approach to the project will be as follows. CNC lathe (Fig. 1) will be used as
the test bed for the project. The piezoelectric actuator will be based on the concept of the
so-called “fast tool servo” (FTS), a (North Carolina State University design is shown in
Fig. 2), which has been in use for years, primarily in diamond turning applications.
However, these devices are designed to allow turning of non-circular shapes, and have
seen little or no application in regards to active control of vibrations for the purpose of
improved surface finish and chatter suppression.
A preliminary design for the FTS exists, and the key components (piezoelectric
stack actuator and amplifier) have been ordered. The remaining machined components
are in the process of being fabricated.
Once the FTS has been fabricated, its baseline
performance will be characterized in non-cutting
condition environments using tools such as
accelerometers, and non-contact laser vibrometers. In
addition, the self-sensing capability of the actuator will
be measured. Cutting condition performance will be
evaluated in face cutting operations on aluminum. In
addition, and time permitting, its effect on chatter
characteristics will also be investigated. Surface finish
will be measured using non-contact profilometry.