- reduced time spent on preventive maintenance, because of better planning
- less overtime worked
- less time given to corrective maintenance
- reduced loss of production due to breakdowns
- less time spent on the administrative tasks of the maintenance service
- longer lifetime of the equipment, because of better preventive maintenance
- reduced energy consumption
No need to say that, as with all other computer aided technologies, maintenance planning and
control should be well structured. The maintenance planning software should be integrated with
all other computer applications like production planning, inventory planning, and Computer
Aided Design, as a better design influences the frequency and amount of maintenance required.
Expert systems could also be useful in inspection and fault diagnosis.
4. A Production and Maintenance Planning Model
Most of the articles on maintenance discuss the determination of the intervals between which
preventive maintenance should be performed, using for instance the age-based model (see e.g.
Zimmerman and Sovereign (1974)).
The simultaneous planning of production and preventive maintenance is a problem that has not
received much attention in the literature. Joshi and Gupta (1986) make use of a production
schedule and equipment failure history to plan maintenance with the aim of minimizing expected
breakdown costs. A dissertation by Pintelon (1990) also develops models for simultaneous
production and maintenance planning, but these determine the time between two preventive
maintenance jobs without taking into account the scheduling of maintenance outside these
intervals.
The model presented in this paper determines whether to schedule preventive maintenance
whenever a new job is to be processed (scheduled). The model trades off the costs of preventive
maintenance, and the sum of inventory holding, corrective maintenance (breakdown costs),
backorder and setup costs. In other words, whenever a job’s processing time is long, or its setup
cost is high, or it is using an expensive material, the model examines whether it is beneficial to
first perform preventive maintenance, or start the job and run the risk of a breakdown. In the
latter case, a job will be delayed, resulting in a possible additional setup and lost material. This
makes the maintenance model a Condition Based Maintenance System, where the conditions are
determined by the length of the processing time, setup cost structure and material used.
In this model, the production environment may consist of several production lines. It is assumed
that each production line has one bottleneck machine. When multiple lines are available, jobs
which cannot be processed on their preferred production line due to preventive maintenance,
may still be processed on the other production lines in case of high backorder costs.
The model developed in this paper is based on a production planning model by Bruvold and
Evans (1985). They developed a mixed-integer program production planning model with
significantly less binary variables as compared to other related research efforts, and which allows
for different objective functions. This production planning model is modified and extended to
take preventive maintenance decisions into account.