Page 18 - Annual Report_AMTDC-2018-19new

AMTDC 2018 - 2019

7. Development of Thermal Compensation Strategy for CNC Lathes

AMTDC (IIT-Madras) team: Ananthakrishna, Anirban Tudu, J. Venkatesh, S.
Karthikeyan, Rino Nelson, P. Pradeep Kumar, Sivasrinivasu Devadula

Industry Partner: Ace Designers Ltd. , Bangalore

Project Highlights

Thermal errors are those that cause a relative displacement between the workpiece and the
tool on account of deformation or expansion of the machine elements due to an increase in
their temperature. Relative movement between the various elements of the machine such as

motors, bearings, ball screws causes heat to be generated at the contact zones and it is this
heat that leads to the deformation of the machine elements. This thermal error contributes to
more than 70% of the dimensional variations (about 50µm) originating from the machine tool.
Such a large variation is not acceptable since the final dimensions are expected to be held
within 10 µm, typically. The current project with the aims to reduce the thermal error to 5 µm,
started with Vantage Lathe 800LM as the thermal error is maximum for this model when
compared to other CNC turning machines. The thermal error component varies from 30µm to
50µm. The thermal behavior obtained from the measurements of thermal error using
temperature and displacement sensors are incorporated in various types of mathematical
models using MATLAB. The prediction model developed has been coded to the microcontroller
and the compensation value calculated by the model is then transferred to the machine
controller. The tool wear offset algorithm has been adopted for compensating for the thermal
error, since the diameter deviation can be compensated with a single input. Using the
compensation methodology described above, the thermal error in the Vantage lathe machine
has been reduced to 7µm as compared to the target of 5µm. The technology can be applied to
any turning machine to improve the accuracy of components produced.

Current Status

The project is almost completed. Error compensation algorithm has been developed
and will be put to test in working condition on the machine which has reduced the thermal
error down to 7µm. A patent for the framework for the development of compensation
system will be filed. The compensation electronics system developed was demonstrated in
IMTEX 2019, held in Bangalore.

18