Sadok Turki

Modelling and analysis for sequentially optimising production, maintenance and delivery activities taking into account product returns

This paper develops and analyses a stochastic optimisation problem with a service level constraint for generating a sequentially optimal plan of production, maintenance and delivery activities in a deteriorating manufacturing system. Stochastic demand along with product returns are both assumed the latter of which allows for restocking products returned by the customer which are still new and thus in saleable condition. A constrained production/maintenance/delivery problem with service level, stochastic demand, delivery time, failure rate and product returned is formulated based on quadratic model. This quadratic formulation is adapted to provide an inventory, delivery, production and maintenance policies. The objective of this paper is to study the delivery time influence on the planning of the production, maintenance and delivery activities. Finally, we present simulation results to illustrate the exploitation of the proposed approach.

Unreliable manufacturing supply chain optimisation based on an infinitesimal perturbation analysis

ABSTRACTThis paper studies the optimisation of a manufacturing/remanufacturing system, which produces one type of product and is composed of a serviceable inventory, two parallel machines, a recovery inventory, two quality inspection centres and customers who demand a constant quantity of product. The proposed system takes into account the withdrawn products and the return of the used products from the market. The manufacturing and remanufacturing products are stored in the serviceable inventory. The used products are inspected then disposed of or stored in the recovery inventory for remanufacturing. The withdrawn products are inspected and stored in the serviceable inventory for selling or stored in the recovery inventory for remanufacturing. The objective of this work is to find the optimal serviceable inventory level that minimises the cost function, then to study the influence of withdrawn products and used products on the value of the optimal serviceable inventory level. Infinitesimal perturbation an...

FPA method for optimal production planning under availability/degradation machine and subcontracting constraint

This work treats an industrial problematic of a manufacturing system M1 subject to random failure and that satisfies a random demand under required service level. To ensure the satisfaction of the demand, it calls up on a second manufacturing system M2 that is a subcontractor and has a stochastic service level. This paper aims to determine an optimal production plan taking into account the degradation of the manufacturing system following its production rate and its availability. The unavailability of the machine M1 is due to the non-negligible preventive and corrective maintenance actions duration. To consider a realistic case of the subcontractor, we consider that is not able to respond to the variation of the demand, and then it assumed that the manufacturer can order a minimum fixed quantity. We then derive an optimal production plan taking into account the degradation of the machine and simultaneously minimising: inventory, degradation and production cost. An algorithm based on finite perturbation analysis is proposed to determine the optimal production plan and the sensitivity study of the availability is presented.

Optimization of Manufacturing Supply Chain with Stochastic Demand and Planned Delivery Time

In this paper, a manufacturing supply chain system composed by a single-product machine, a buffer and a stochastic demand is considered. A stochastic fluid model is adopted to describe the system and to take into account stochastic delivery times. The objective of this paper is to evaluate the optimal buffer level used in hedging point policy taken into account planned delivery times, machine failures and random demands. This optimal buffer allows minimizing the sum of inventory, transportation, lost sales and late delivery costs. Infinitesimal perturbation analysis method is used for optimizing the proposed system. Using the stochastic fluid model, the trajectories of buffer level are studied and the infinitesimal perturbation analysis estimators are evaluated. These estimators are shown to be unbiased and then they are implanted in an optimization algorithm, which determines the optimal buffer level in the presence of planned delivery time. Also in this work, we discuss the advantage of the use of the infinitesimal perturbation analysis method comparing to classical simulation methods.

Optimal maintenance plan for two-level assembly system and risk study of machine failure

This paper deals with the optimisation of two-levels assembly system planning. This system is composed of a single machine, inventories at levels 1 and 2 for stock keeping components to assembly and final assembled product. It assumed that the machine processes all assembly operations and is subject to random failure. A mathematical model is developed to incorporate a supply planning for two-level assembly systems under stochastic lead times and breakdowns machine. A preventive maintenance plan is carried out to reduce the frequency of the corrective maintenance actions. This work has double goals. The first one is to find the optimal order release dates for the different components at level 2 and the optimal preventive maintenance plan. The second one is to quantify the risk due to machine failures which have an impact on the lead-time of the finished product. To consider the maintenance actions, preventive maintenance actions are perfectly performed to restore the machine to state “as good as new”, minimal repair is considered at failure. The model minimises the total cost, which is the sum of inventory holding cost for components at levels 1 and 2, backlogging and inventory holding cost for the finished products and maintenance costs. To illustrate the effectiveness of the proposed model, different meta-heuristics are applied; the genetic algorithm shows the most suited to our analytical model, the optimal release date founded by this algorithm allows finding the optimal preventive maintenance plan. The obtained optimal maintenance planning is used in the risk assessment in order to find the threshold repair period that avoids lost profit.

Study of the E-Maintenance Service in E-Logistic Supply Chain

This paper studies the case of supply chain company in E-commerce framework. The proposed company produces and sales online electronics products such as laptops, tablets, or smartphones. All products are sold under warranty for a specific period. The company ensures during the warranty period the maintenance of the products. Two cases of maintenance service are considered in this paper: in the first the company ensures conventional maintenance service and in the second the company ensures E-maintenance service. Thanks to service oriented modeling we were able to model both cases and to define the different tasks and services in the company. Then we derived a mathematical model to compute the profit in both cases. The objective of this work is to evaluate and compare both cases of company. Numerical results are presented to discuss the choice of the suitable case.