Thermal test piece for 5-axis machine tools

The accuracy of 5-axis machine tools is a key factor to modern manufacturing of multi-axes machined workpieces. Up to 75% of errors on manufactured workpieces are caused by thermally induced errors of machine tools. In this paper a thermal test piece for evaluating thermal errors of machine tools equipped with rotary tables is introduced. In comparison to geometric test pieces, which detect geometrical errors of machine tools only, the developed thermal test piece visualizes thermally induced errors in X-, Y- and Z-direction as well as two additional angular errors at the tool center point (TCP) of 5-axis machine tools over time. Further, the thermal material expansion error of the test piece on centric clamped machined workpieces can be evaluated with the new thermal test piece. The presented thermal test piece is machined during a corresponding eight hour test cycle and tested on two 5-axis milling machines with different axis configurations. The thermal test piece can either be evaluated with a coordinate measuring machine (CMM) or manually with handheld measurement devices such as dial gauge, micrometer and straightedge. The thermal behavior of the two machine tools is also investigated, following the ISO 230-3:2007 regarding thermal errors of machine tools, under no-load or finishing conditions using the R-Test measurement setup. The resulting workpiece errors evaluated by using the thermal test piece are compared to the machine tool measurements. A good correspondence between the R-Test measurements and the thermal workpiece errors can be shown. CMM and handheld measurements are both capable to detect the thermal machine tool errors.