Thermal errors of a 5-axis CNC milling centre equipped with different spindle units

Abstract

Thermally induced errors are dominant sources of inaccuracy and are often the most difficult types of errors to reduce today. Software compensation of thermally induced displacements at the TCP is a widely employed technique to reduce these errors due to its cost-effectiveness and ease of implementation. Furthermore, machine tool manufacturers frequently offer a particular type of machine tool in multiple versions, where each version is equipped with a different spindle unit. This leads to different thermal deformation behaviour depending on the specific spindle unit mounted in the machine tool. To demonstrate this difference, an experimental research on a three 5-axis CNC milling centres of the same type equipped with three different spindle units is presented in this paper. Experimentally obtained thermal errors at the TCP from 3 machine tools with different mounted spindle units are mutually compared, showing a significant variation in thermal errors in the Z direction depending on the spindle unit. This fact should be taken into consideration in development of thermal error compensation models, as shown in the case of a modelling approach using transfer functions for a tested 5-axis CNC milling centre.