Mustapha Sali

The bullwhip effect in supply chains: a study of contingent and incomplete literature

The bullwhip effect (BWE) describes a phenomenon that involves the increasing amplification of demand variability along a supply chain (SC). The BWE has been a subject that has received continuous attention from researchers over the past 15 years and is a concern for SC managers because it is a major cause of efficiency and effectiveness loss in SCs. Information sharing between actors in an SC is usually considered to be one of the primary means to minimise the BWE. Approximately 50 articles published in major journals on these topics are studied in this article. An analytical framework is used to highlight the contingent character of the conclusions proposed by the authors. In this review, we identify the existence of significant gaps in the literature, especially concerning the BWE when it occurs in the productive part of the SC.

An empirical assessment of the performances of three line feeding modes used in the automotive sector: line stocking vs. kitting vs. sequencing

In high diversity, Just In Time production environments, mixed-model assembly lines aim at producing a large amount of end products that use alternative variants of components used in the assembly process. Therefore, the availability of parts required at the border of the assembly line is critical for the production process. To ensure the availability of parts needed on the line, three line feeding modes are commonly used in practice: line stocking, kitting and sequencing. The relative performance of each mode, in terms of average total operating cost, depends on various factors such as the diversity of components, parts’ physical features (i.e. weight and volume), to name a few. The impact of such parameters on the performance of line feeding modes remains still weakly studied in the literature. Through an empirical approach based on a real case, our study aims at evaluating the average total cost pertaining to each mode. The total cost includes parts preparation before assembly, picking, in-plant transportation and storage costs. A thorough comparative study enables then to characterise situations which make one mode less costly compared with the others. Each situation corresponds to specific values taken by parameters that are considered in the cost formulation.

Monitoring the production of a supply chain with a revisited MRP approach

This paper examines the centralised monitoring of an upstream supply chain (USC) in the context of a mass customisation production system. We propose an adaptation of the material requirement planning framework to manage demand uncertainty at each stage of the USC. New analytical relations that exploit structural information on demand beyond the frozen horizon are developed for efficient decision-making and appropriate information sharing among the productive supply chain units. A numerical example to illustrate the implementation of the new analytical relations is provided, and a synthesis of benchmarks performed in the automotive industry is presented.

Mass customisation impact on bill of materials structure and master production schedule development

The customisation of a vehicle on a production line results from the assembly of several hundreds of alternative components. Bills of Material (BOM) are usually made for operational purposes (to define the list of components to be assembled on a vehicle), for planning (to anticipate component procurement needs) and for commercial needs (guide customer choice and prepare sales forecasts). In the automotive industry, the diversity of end products which results from this combinatorial process (several millions) is such as no solution proposed in the literature allows to easily list the BOMs for all these vehicles. In our paper, we describe and theorise a solution used for many years by several carmakers, which consists in introducing a commercial description of the products in addition to their common organic representation. We show that this solution is an extension of the generic and modular BOM theory, recognised to be the most advanced solutions proposed in the literature. While fully meeting commercial and production control needs, this product description paradigm has limitations when it comes to determining the Master Production Schedules (MPS) at end product level beyond the frozen horizon, as performed by several automakers. An alternative approach defining MPSs at alternative component level is proposed in the literature. However, this approach also has several drawbacks that we point out. To overcome these issues, we propose a number of possible strategic and organisational tracks of improvement.

Optimal stock-out risk when demand is driven by several mixed-model assembly lines in the presence of emergency supply

This article focuses on the calculation of the optimal stock-out risk when resorting to emergency supplies is allowed. The studied context is a supply chain where several distant mixed-model assembly lines trigger the demand of a component used for assembly. When the cumulated lead time of a component exceeds the frozen horizon of the material requirement planning (MRP) of at least one of the assembly lines, its demand becomes stochastic. This leads to a mix between production to stock and production to order for the component of interest. The periodic replenishment policy is designed to address demand uncertainty in consistence with MRP information. To prevent stock-out propagation along the supply chain, the emergency supply is used as a last resort. The calculation of the optimal order-up-to-level and its associated optimal stock-out risk are based on a single-period trade-off between holding cost and emergency supply cost (transportation and production).

Optimal stock-out risk for a component mounted on several assembly lines in case of emergency supplies

This article focuses on the calculation of the optimal stock-out risk for a component, which is used by alternative modules mounted on several assembly lines. The studied context is a supply chain dedicated to the mass production of highly diversified products, which is common in the automotive industry. The Material Requirement Planning (MRP) approach is adapted for the monitoring of this chain; however, the distance between the production units leads to mix between production to stock and production to order for the component of interest. To prevent stock-out propagation along the downstream part of the supply chain, use of an emergency supply is triggered prior to its occurrence. The definition of the optimal safety stock and the associated optimal stock-out risk, are based on a monoperiod model that considers the cost of a safety stock and the costs incurred by the emergency supply (transportation and production). The analytical solutions that are dependent on these costs are illustrated in this study.