Integrated Geometric Error Compensation of Machining Processes on CNC Machine Tool

Abstract

Kinematic errors due to geometric inaccuracies in machining system cause deviations of tool positions and orientation from being machined point on the workpiece, which consequently affect geometric accuracy of the machined surface. This paper presents an integrated geometric error model of machining system and compensation method on machine tools. Regarding a machine tool, fixtures, workpiece and tool as an assembly, an integrated geometric error model has been established. The integrated error is modeled by the propagation and the accumulation of errors based on Jacobian-Torsor theory. It is different with previous model, in this model, all the geometric errors of machining system are converted into the machine tool instead of the workpiece machining surface. As is well known in the machine tool, there are 21 geometric error of a 3-axis milling machine tool, which can be measured by laser interferometer. Based on this integrated model and machine tool error, the combination of geometric errors of machining system reflect on the machine tool can be predicted. Finally, a new compensation method is proposed to realize the error compensation, NC program is corrected corresponding NC codes according to the predicted errors during virtual machining before it is fed to the actual machining. A case demonstrates the application of how the method could be used in error compensation for machining processes.