Maintenance Decision Model Research About The Key-subsystem Of The CNC Lathe

Numerical control(NC)lathe plays an important role in the production of mechanic parts.Due to the complicated structure and frequent work of NC lathe,many failures would happen during the operation of NC lathe.Recent years,according to the statistics,the maintenance costs produced by the failures stayed at a high level and occupied about thirty percent of the whole life cost.Now the user enterprise has the weak awareness of the maintenance,they repaired the machine tool as long as it broke down.In order to reduce the failure frequency and lower the maintenance cost of the NC lathe,in this paper,a suitable maintenance decision model was designed for the subsystems of the NC lathe.And the specific research content was as following:1.Each subsystem of the NC lathe has different function,therefore each the important degree of the subsystems should be calculated and then the key-subsystems can be acquired.In this paper,the improved TOPSIS was combined with the grey correlation degree method to establish the importance evaluation mode l for the subsystems of CNC lathe.According to the operation history and maintenance features of CNC lathe,eight importance evaluation indexes were selected: Required experts grade each subsystem under the corresponding indexes and then calculated the mean value formed into the decision matrix.Used the improved TOPSIS with the grey correlation methods to compute the importance degree.Then the key-subsystem can be required.2.After preventive maintenance,the failure rate of the subsystem was influenced by the increasing failure rate factor and age reduction factor.In this paper,three models were established to solve the preventive maintenance for subsystems of CNC lathe,they obeyed these conditions respectively: lowest reliability limit,maximum availability and minimizing a single cycle cost rate.Example was given to verify the effectiveness of the lowest reliability limit condition model.Finally,lowest reliability limit condition was used to compute the best preventive maintenance strategy for the key subsystems.3.In order to reduce the shutdowns and downtime losses,the concept of reliability opportunistic maintenance(35)R was introduced to integrate the preventive maintenance points of the key-subsystem of CNC lathe.Assumed that early preventive maintenance for the subsystem would cause a waste of life and formed penalty costs.The preventive maintenance cost,preventive maintenance stop loss,preventive overhaul cost,minimal cost and penalty cost were inte grated considered among the operation of the CNC lathe.In order to get the optimal opportunistic maintenance threshold(35)R,cost minimization model and maximum availability model were established respectively.Examples were given under the opportunity maintenance model,and the downtime numbers and maintenance costs decreased sharply.In this paper,the increasing failure rate factor and age reduction factor were combined together with to consider the effect on the function of the failure rate after preventive maintenance and verified that the reliability limit method has the effectiveness to establish the preventive maintenance model.When establishing the opportunity maintenance model for the key-subsystem,penalty costs were considered which was more realistic.This article is of great value to select maintenance strategy for the key-subsystem of the NC lathe.