Machining, Measurement, and Control Laboratory

Prediction and compensation of machining geometric errors of five-axis machining centers with kinematic errors
M. Sharif Uddin, Soichi Ibaraki, Atsushi Matsubara, Tetsuya Matsushita

Kinematic errors due to geometric inaccuracies in five-axis machining centers cause deviations in tool positions and orientation from commanded values, which consequently affect geometric accuracy of the machined surface. As is well known in the machine tool industry, machining of a cone frustum as specified in NAS979 standard is a widely accepted final perforance test for five-axis machining centers. A critical issue with this machining test is, however, that the influence of the machine’s error sources on the geometric accuracy of the machined cone frustum is not fully understood by machine tool builders and thus it is difficult to find causes of machining errors. To address this issue, this paper presents a simulator of machining geometric errors in five -axis machining by considering the effect of kinematic errors on the three-dimensional interference of the tool and the workpiece. Kinematic errors of a five-axis machining center with tilting rotary table type are first identified by a DBB method. Using an error model of the machining center with identified kinematic errors and considering location and geometry of the workpiece, machining geometric error with respect to the nominal geometry of the workpiece is predicted and evaluated. In an aim to improve geometric accuracy of the machined surface, an error compensation for tool position and orientation is also presented. Finally, as an example, the machining of a cone frustum by using a straight end mill, as described in the standard NAS979, is considered in case studies to experimentally verify the prediction and the compensation of machining geometric errors in five -axis machining.
Key Words:   five-axis machining center, kinematic errors, DBB method, machining geometric errors, the cone frustum workpiece, Error compensation