Economic production quantity models with variable production rates

This thesis focuses on Economic Production Quantity problem. The EPQ problem is concerned with the selection of the optimal production time for a production process. The literature in the area of EPQ focused more on either the selection of production rate or the production time. We have developed a mathematical model for the selection of optimal production time in case the production rate shifts to a value lower than the starting value for the case when this time to shift is deterministic. The second model is developed for the case when this time to shift is a random variable with known general distribution. The third model is an extension of the second model to include the possibility of restoration of the system to the original production rate in case a shift is detected during process inspection. The fourth model includes the possibility of preventive maintenance to reduce the effective age of the system to decrease the probability of shift. The fifth and final model extends the general model by relaxing the assumption of deterministic production rate after the shift. Results show that for the case where the production rate shifts, the expected cost per unit time will be forced higher and also the system is forced to operate for longer periods of time. The thesis is concluded by suggesting a number of recommendations for future research.