Efficient thermal error prediction in a machine tool using finite element analysis

Thermally induced errors have a major significance on the positional accuracy of a machine
tool. Heat generated during the machining process produces thermal gradients that flow
through the machine structure causing linear and nonlinear thermal expansions and distortions
of associated complex discrete structures, producing deformations that adversely affect
structural stability. The heat passes through structural linkages and mechanical joints where
interfacial parameters such as the roughness and form of the contacting surfaces affect the
thermal resistance and thus the heat transfer coefficients. This paper presents a novel offline
technique using finite element analysis (FEA) to simulate the effects of the major internal heat
sources such as bearings, motors and belt drives of a small vertical milling machine (VMC)
and the effects of ambient temperature pockets that build up during the machine operation.
Simplified models of the machine have been created offline using FEA software and evaluated
experimental results applied for offline thermal behaviour simulation of the full machine
structure. The FEA simulated results are in close agreement with the experimental results
ranging from 65% to 90% for a variety of testing regimes and revealed a maximum error range
of 70 μm reduced to less than 10 μm.