Abstract: The production and maintenance activities share the same system in reality, so the conflict is inevitably generated. If the arrangement of the production plan and the maintenance schedule are not reasonable, the shortage of the products and the improper maintenance (inadequate maintenance or excessive maintenance) may occur. To avoid this negative influence, the integrated model of the production planning problem of discrete manufacturing industry and non-cyclical preventive maintenance is proposed in this paper. The finite production planning horizon is composed of several equal-length periods. in each period, the demands of multi product should be satisfied by the production quantity in this period and the inventory of last period, otherwise, the backorder will happen. The non-cyclical preventive maintenance can be carried out at the end of some production periods, and the minor repair is used to deal with system failures. The occupation of production capacity is composed of maintenance and system setup. In each period, the time can be used to product is equal to the length of the period minus the maintenance and setup time, and the actual running time of system is used to formulate the failure numbers. Furthermore, the maintenance time of failure can be presented. Then' the integrated production and maintenance model is developed in the form of mathematical programming. The objective of the model is to determining the optimal production panning and preventive maintenance sequence that minimizes the sum of the production cost, inventory cost, setup cost and maintenance cost. Based on the production data of steel grating gathered from a steel facility, a case study is presented to illustrate the integrated model, the optimal production plan and the optimal maintenance schedule are determined simultaneously. Moreover the result shows that the optimal maintenance schedule is not cyclical, since the non-cyclical maintenance policy presents more maintenance sequences than that presented by cyclical maintenance policy.

Key words: production planning, inventory, preventive maintenance, delay-time