Vincent Giard

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.

Scheduling coordination in a supply chain using advance demand information

In an environment of mass customisation where demand information can be placed in advance with sequencing orders, the question of the best use of this information arises in a supply chain. This situation led the authors to analyse the efficiency of current mechanisms of scheduling coordination when suppliers’ processes are not completely reliable. Policies such as periodic replenishment or the kanban system, characterised by a replacement of the items to consume, cannot be exploited effectively with the current rules. This article presents and justifies new scheduling coordination rules allowing synchronous production in an unreliable environment. This new approach has been benchmarked in the automotive industry as an appropriate method to avoid stockouts and decrease the safety stock.

Production à flux tirés dans une chaîne logistique

Le choix d’un pilotage de la production entre une approche à flux tirés et une approche à flux poussés est moins simple qu’il ne le paraît lorsque l’on prend en compte le périmètre des chaînes logistiques ; en fait, il s’avère en général nécessaire de combiner ces deux modes de pilotage pour respecter au mieux les délais clients, de plus en plus courts, sans augmenter les coûts. Ces couplages ne sont pas indépendants des caractéristiques de la chaîne logistique, des produits à fabriquer et de la régularité de la demande et font appel à différentes formes de pilotage. On examinera ici une des approches les plus connues, le système kanban utilisé avec succès sous certaines conditions en particulier celle de la stabilité de la demande. On analysera l’usage du système kanban dans des environnements violant les hypotheses classiquement faites dans ce domaine, ce qui permettra de mettre en evidence les conditions de robustesse de ce type de pilotage. La remise en cause du régime de croisière dans le système kanban complique un peu l’analyse des modalités de pilotage des flux sur la chaîne logistique et pousse à imaginer de nouvelles règles de pilotage pour permettre la synchronisation des productions dans la chaîne logistique.

A new need for safety stocks in a supply chain dedicated to customized mass production

In a supply chain designed for the production of a wide variety of goods, the production schedule creates an ordered list of all the alternate components that will be mounted on the same work station of the chain. Supplying these components may have to respect some transportation-related constraints. From there systematically follows a time-gap between orders and deliveries. This mechanism, commonly called rank-change, may be analyzed with the help of the multinomial distribution associated with these alternate components. Only a simulation approach is relevant because an analytic approach is not possible. Such an analysis allows assessing the importance of the need to form safety stocks because of lot-sizing, even though requirements are known.

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.

Standardization, Commonality, Modularity: A Global Economic Perspective

This paper deals with the problem of simultaneous standardization of a set of modules and of multiple sets of components that may be combined in these modules. The aim is to minimize future costs. The components and modules, whether already existing or yet to be created are not related to predetermined BOMs. The problem takes into account coupling constraints between components because not all components included in a module may be coupled (coupling restriction), although some of the restrictions can be lifted through “junction components”. Our approach is readily implemented and significantly improves decisional consistency when compared to the standardization approaches that deal with the problem in isolation as opposed to globally. It also matches the level of detail used in large organizations for forecasting purposes. This approach is illustrated with a real case study of great dimension.

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.

Scheduling of open-pit phosphate mine extraction

Open-pit deposits are often characterised by a stack of layers of different geological nature. Some layers are worthless while the ore of the others is of a varying economic value depending on grade. To reach a layer, it is necessary to have first removed the upper layers above the extraction zone. This action results in uncovering the layer in this particular place and in facilitating access to the layers below. This extraction process involves a series of 2–7 basic operations; each one is performed by a machine, some of which are able to perform up to three different operations. Ensuring the consistency of mining extraction scheduling over a few months, in order to meet known or forecast demand, is a challenging task. A mining extraction model based on mathematical programming is proposed but it is hardly usable, due to its size. Therefore, a model based on a Discrete Event Simulation, is created to test how ore supplies are affected by the tactical and operational decisions relating to the choice of parcels to be processed and to the allocation of machines to the different basic operations.