Thermography in the Studies of the Thermal Characteristics
of Numerically Controlled Vertical Knee-Type Milling Machines

Roman Staniek & Leszek Rozanski

Poznan University of Technology, IMt , Pl. M. Sklodowskiej-Curie 5

60-965 Poznan, Poland,

phone:+48 61 6653595, fax: +48 61 6653570 e-mail:

(Poster presentation)

Key words: IR thermographic diagnosis, thermal deformations

The continuous progress connected with production of machine tools makes difficult the realization of methods improving their quality. The particularly difficult problem is to assure the thermal stability of machine tools. The thermal displacements in machine tools should be relatively small and should be independent on varying work conditions. As the result of the heat that has been created in machining zone as well as of the heat occurring from internal sources (motors, bearings, clutches, breakers and so on) and external sources (from environment) the elements of machine tools get hot, the thermal displacements occur and, as the result the quality of machining may be decreased. It can be stated generally that there are four main regions where thermographic diagnosis may be significant. They are as it follows [1]:

  • investigation and designing process,
  • final testing during mounting the machine tools on their work position,
  • final investigations connected with supervision and diagnosis of the incorrect work,
  • investigations connected with compensation ot the thermal disturbances (displacements).

Application of the systematic methods in thermographic diagnosis for final acceptance of machines and supervision and diagnosis of machines and technological devices, is still not so popular. The thermographic system seem to be very good devices in order to apply them for various investigations.

The thermal characteristics of a machine tool, defined by the distribution of temperature on the various surfaces of its frame, result from the interactions of the heat fluxes arriving at the tool and emitted by it into the environment. The ratios of the various heat sources in the total energy balance depend on the types of the sources, the conditions in which they operate and the design of the machine tool. The essential factors affecting the values and distribution of temperature are the locations and efficiencies of the heat sources, and the intensities of the fluxes which they emit into the environment.

The technical requirements for the studies and determination of thermal deformations are specified in the standard ISO/FDIS 230/3, which stipulates that the following parameters be determined:

•thermal deformation due to changes in the ambient temperature;

•thermal deformation due to the motion of the spindle;

•thermal deformation due to the linear motion of the table.

All of these heat sources produce certain effects on the thermal expansion of the subassemblies of a machine tool, and consequently also on the accuracy and repeatability of the positioning.

The methods of the compensation for thermal deformations applied in high-precision machine tools, base on complex systems connected to the CNC systems of the tools (or to a part thereof) [2]. The former systems feature temperature or displacement sensors installed in selected locations within the machine tool and generating signals which on entering the CNC system produce additional, compensating movements of the tool with respect to the workpiece. Such movements are possible only if thermal deformation is monitored. The locations of the temperature sensors should ensure the optimum correlation of the measured temperature with the deformation which the CNC system adjusts numerically. Studies have shown that thermographic measuring methods may be useful in the optimization of the locations of contact temperature sensors by means of the criterion of the optimum correlation between the patterns of the changes of deformation and of temperature. The relationships between the measured changes of temperature and the thermal deformation of the tool with respect to the workpiece are determined using software based on Artificial Intelligence (AI), e.g., Neural Networks (NN), Genetic Algorithms and Fuzzy Logic [3].

Fig. 1. Measuring station for thermographic studies of the thermal condition of milling machines.

Fig. 2. A thermogram of the fast head and the overarm of the fast head of a vertical milling machine.

References

  1. Poloszyk S., Różański L.: Thermographic Diagnosis Station of Machines. 7th International DAAAM Symposium, Wienna 1996
  2. Kurtoglu A., Sohlenius G.: The Accuracy Improvement of Machine Tools. Annals of the CIRP Vol. 39/1, 1990
  3. Mitsuishi M., Warisawa S., Hanayama R.: Development of an Intelligent High Speed Machining Center. Annals of the CIRP Vol. 50/1, 2001