Oussama Ben Ammar

Mathematical Model for Supply Planning of Multi-level Assembly Systems with Stochastic Lead Times

The deal for industrial companies is to satisfy their customers with the best quality, the most reliable lead times, and the lowest costs. One of the keys to achieve it is in the inventory control in the Supply Chain. Moreover, it is mandatory to possess necessary components in order to produce the requested products by the due date. But, as the components lead time is an unpredictable parameter, it is difficult to take it into account correctly. In this paper we deal with this question considering that each component has a fixed unit inventory cost; the finished product has an inventory cost and a backlogging cost per unit of time. Then, a general mathematical model for supply planning of multi-level assembly system is presented to calculate the expected value of the total cost which equals to the sum of the inventory holding costs for the components, the backlogging and the inventory holding costs for the finished product. The aim is to propose tools to adapt and parameterize the MRP method under lead time uncertainty.

Supply Planning and Inventory Control under Lead Time Uncertainty: A Review

Abstract In literature, most papers examine several stochastic demand processes where order lead times are constant. In reality, lead time is rarely constant; unpredictable events in the supply system cause unpredictable delays. It is true that in certain special cases, lead time uncertainty has essentially no effect and can be ignored. Nevertheless more often, lead time fluctuations strongly degrade performance, just as demand uncertainty does. Seemingly, lead time uncertainty has been neglected for a long time in favor of studying demand uncertainties. Industry agrees that it is overdue and there is a need to rectify this oversight. Nowadays, this gap in research activity begins to be filled in order to respond to companies having non-deterministic lead-times constraints. This paper reviews some of existing literature of supply planning under uncertainty of lead times. The extensive literature review that we compiled consists of citations from 1970 to 2012. A classification scheme for supply planning under uncertainty is defined.

Analysis method of the relations between MRP parameter and performance indicator based on a literature review

Since the 1970s, extensive research has been conducted to improve the performance of MRP systems (Material Requirement Planning). We identified 86 papers in this domain. These papers examine the influence of configuration on performance measurement indicators in defined operating and instability conditions. These studies, in principle, provide production planners with a decision-making aid. The initial objective of this paper is to measure and characterize the accumulated knowledge in the 86 papers identified. The potential generalization of the knowledge gained is subsequently discussed. We propose a method of analysis of this knowledge.

Reducing the Research Space of Possible Order Release Dates for Multi-level Assembly Systems under Stochastic Lead Times

This paper proposes tools which will be used to optimize multi-level assembly under lead time uncertainty. One type of finished products and several types of components are considered. We suppose that each component has a fixed unit inventory cost and the finished product has backlogging and inventory holding costs per unit of time. The lead times of components are discrete random variables, and the costumers demand of the finished product is known. A reduced space of research is presented to strengthen optimization methods which have been applied for minimizing the sum of the average inventory holding cost for components and the average backlogging and inventory holding costs for the finished product.