Thermal error modelling of a three axes vertical milling machine using Finite element analysis (FEA)

Thermal errors in machine tools have a detrimental effect on the accuracy of components they produce. In order to reduce the influence of thermal errors, the propagation of heat through the structure of the machine needs to be understood. The modelling of thermal error of small three axes vertical milling centre (VMC) machine tools is introduced in this paper. Firstly, a thermal imaging camera and non-contact displacement transducer (NCDT) sensors were used to measure the temperature and thermal deformation in X, Y, Z axes respectively during spindle heating and cooling cycles. Secondly, a model of the VMC was created using SolidWorks software and simulated using finite element analysis (FEA). The boundary conditions are calculated according to measured parameters like, temperatures of machine structure, heat transfer coefficients and ambient temperature. Of particular importance is the heat power of heat generating components in the machine such as the main spindle motor and bearings. These parameters vary with machine use and are calculated using energy balance calculations and thermal imaging data. Finally, the FEA simulated results are obtained and are in close correlation with the experimental results. Such accurate FEA simulations permit offline assessments to be made of temperature gradients and displacements in machine tools structures, reducing the need for expensive on-line testing. Furthermore, correlation coefficient analysis is employed to validate the simulated model temperature;
the thermal error was reduced up to 90%, from 35