Towards a Downtime Cost Function to Optimise Machine Tool Calibration Schedules

A high degree of accuracy of production machines, especially machine tools, is often highly desirable. Understanding capability, maintaining or improving the performance of the machine requires a periodic full calibration. The idea of maintaining machine accuracy by regular calibration is analogous to using predictive maintenance methods to reduce the risk of machine breakdown. Studies in the field of predictive maintenance have resulted in cost calculations for the downtime associated with machine failure.
Models have been presented to determine optimal intervals between repairs by minimising global maintenance costs. However, very little work has concentrated on optimising the frequency of machine tool calibration by assessing the downtime cost considering the contribution of both technical and commercial factors.
This paper presents a cost function that forms the basis of a strategy for scheduling machine tool calibration which takes into account these influences on part tolerance.