Thermal volumetric effects under axes cycling using an invar R-test device and reference length

• Investigation of volumetric thermal effects in five-axis machine tools.
• Capability of R-test is expanded with thermally invariant calibrated reference artifact.
• Rotary axes are major contributors to thermal errors.
• Cycling a rotary axis affects the error motions of a neighboring linear axis.

Thermal errors of machine tools are in part caused by the variation of ambient temperature as well as the heat internally generated by the machine. These deformations are a major source of quasi-static machining errors and are thought to be related to temperatures and temperature gradients within the machine structure. This article presents a study of the thermal volumetric behavior of a five-axis machine tool. The study uses direct volumetric error measurements within the machine work volume for specific combinations of five-axis commands. Thermally induced volumetric distortion errors are studied in relation to a specifically designed machine activity sequence during which the power at each of the five-axis motors and the spindle are measured. The experimental measurement setup consisting of a thermally stable volumetric error sensor and a reference scale bar is presented. The study allows quantifying the effect of every axis’ activity on the Cartesian components of the volumetric distortion. Rotary axes are found to be the major contributors to the tested machine's thermal errors. Thermal coupling is observed whereby the activity of a rotary axis strongly affects a neighboring linear axis.