Load controlled process window analysis of feed controlled CNC grinding

摘要

Grinding processes offer a huge range of parameters affecting quality and quantity of the optical elements being produced. Systematic optimization can reveal unexploited potential even in already "stable and efficient" processes. In this paper we describe a method for optimizing CNC grinding processes under industrial conditions by applying a Preston-based approach. As already reported by Mr. Preston, for load controlled grinding processes, the workpiece material removal rate (MRR) is proportional to the applied tool pressure (P) multiple the applied relative speed between tool and workpiece (vr): MRR = c*P*vr. Consequently, while maintaining the relative speed (vr = const), there is a linear dependency of MRR on the applied pressure P existing within the process window. The method reported in this paper uses the inverse conclusion that outside of the process window, the linear dependency of MRR on P is not valid any more. This effect is being used to determine the process window of feed controlled CNC grinding processes, since spindles and slides of modern feed controlled CNC grinding machines have finite stiffness values. Therefore, we can apply a load controlled approach to determine the process window of feed controlled grinding processes. To that aim, a dynamometer was mounted onto a fixed abrasive, feed controlled, standard optics CNC grinding machine, monitoring tool pressure in situ and in process for different values of CNC machining parameter sets such as tool rotation, workpiece rotation and infeed speed etc. Experimental data will be presented determining the process window of various CNC grinding processes demonstrating that applying grinding process parameter sets within the process window boundaries guarantee a stable and predictable production with high yield values.