Lucio Zavanella

The consignment stock of inventories: industrial case and performance analysis

The ‘‘Consignment Stock’’ technique is a novel approach to the management of inventories in supply chains. It is based on an improved collaboration between the company and its suppliers, one that is acquiring growing importance in industrial environments, as the authors have found in Italy. The main aim of the present work is to describe the technique itself, thus underlining its potential benefits and pitfalls. The case proposed refers to a company manufacturing components for the automotive industry. Essentially, the company offered its suppliers the opportunity of stocking part of the items in its own warehouses, with the agreement that they would guarantee over time an inventory level between a set minimum and a maximum value. r 2002 Elsevier Science B.V. All rights reserved.

Single-vendor single-buyer with integrated transport-inventory system: Models and heuristics in the case of perishable goods

We consider the problem of shipping a set of products from a single origin (the vendor) to a common destination (the buyer) with the objective of minimizing the sum of the inventory and transportation costs, when a set of shipping frequencies is given and products are assumed to be perishable. We provide a mixed integer linear programming model for the problem and propose the modification of known heuristic algorithms to solve it. Extensive computational results show how some of the modified heuristics are extremely efficient and effective.

Layout design in dynamic environments: Strategies and quantitative indices

The design of a layout is a critical step, which may have a major influence on the success of a plant, particularly when demand is uncertain and variable. In order to counter this variability, one of two strategies is generally adopted, i.e. the identification of either a robust or an agile layout. This study proposes the adoption of indices that will help in identifying the strategy to be preferred. Starting from the case of a single row layout, the results of an experimental campaign are presented and discussed in order to show the efficacy of the indices themselves. Their calculation takes into account the profile of demand over time together with the product route sheets.

A joint economic lot size model with price and environmentally sensitive demand

This paper presents a joint economic lot size (JELS) model for coordinated inventory replenishment decisions considering price and environmentally sensitive demand. It assumes a single product that flows along a two-level supply chain (vendor–buyer). The buyer’s demand is linear and sensitive to the product’s price and its environmental performance. A capital investment is considered necessary to improve the production process resulting in an indirect improvement of the product’s environmental quality. A mathematical model is developed to represent this situation and solved to maximize the total profit of the supply chain for: (1) the vendor’s production lot size quantity and the number of shipments to the buyer, and (2) the selling price and the amount invested to improve the production process. Numerical examples are provided with their results discussed.

A consignment stock coordination scheme for the production, remanufacturing and waste disposal problem

This paper extends the model of a production, remanufacturing and waste disposal system by adding a buyer (retailer) to the vendor’s system to form a two-level forward/reverse supply chain. The vendor and the buyer are assumed to operate according to a consignment stock policy. A mathematical model is developed for the cases when the production and remanufacturing batches are of different and equal sizes. The model also accounts for transportation, inspection and sorting costs. Numerical examples are provided and results are discussed. The results show that the collection rate of used items and the repairable rate have a significant impact on the total cost of the system and the batch sizes. It was suggested that it may not be possible to operate a system like the one described in the paper at its maximum environmental edge without receiving some incentives or tax brackets. Another possibility is for the system to undergo a continuous improvement process to reduce its operational costs, which may require additional investment.

Layout design in dynamic environments: analytical issues

The paper discusses the layout problem for a productive environment affected by variability of demand (dynamic environment). A conceptual framework of the layout flexibility is discussed, according to the concept of layout robustness. An analytical approach extends the technique adopted for the optimal layout determination from the static to the dynamic context. For an assigned layout problem, an example shows how the analytical approach may be applied to the calculation of the probability distribution of the cost function. From this basis, a measure of the layout robustness is proposed and commented on, in order to give useful advice to those in charge of layout planning and control and to highlight the potential use of the theoretical issues discussed.

Measuring and benchmarking productive systems performances using DEA: an industrial case

The study presents a comprehensive analysis of the efficiency over time of five steel plants pertaining to one of the largest private groups in Italy. In particular, the paper proposes a new technique for plant performance measurement that is able to help the management in formulating manufacturing strategies according to the performance measurements usually available in industrial environments. The analysis is carried out by the methodology of Data Envelopment Analysis (DEA), taking advantage of several improved solutions proposed in the literature adopted to augment the discriminating resolution. Results obtained are summed up by means of suitable cluster analysis. Finally, thanks to the dual formulation of DEA, a technical and economic analysis is proposed with reference to the productive units identified as inefficient. The technique proposed was successfully applied to the industrial case of reference and it can be easily extended to every manufacturing context.

F.M.S. tool supply in a stochastic environment: Strategies and related reliabilities

In the evolution of manufacturing processes a fundamental role has been played by the changes in the organization of production, as in the case of the flexible manufacturing systems (FMS). The present study analyses the problem of the tool supply and refurbishment in a FMS. The interest for an analysis of this kind arises when the influence of the stochastic nature of the tool life on the reliability level of the machining jobs is to be evaluated. As to this problem, an analytical procedure is suggested and the obtained values are compared with the reliability level set at the planning stage and with the actual reliability, evaluated by means of the simulative procedure. The effectiveness of different strategies of tool replacement and machining operation check is also considered and evaluated. The peculiar situation of machining job interdependencies is discussed at the end of the study, thus investigating the reliability of a cutting operation not solely dependent on the stochastic nature of the involved tool, but also depending on the nature of the tools preceding it in the machining cycle.

Payment schemes for a two-level consignment stock supply chain system

Two-level supply chain with consignment stock agreement.Different payment schemes were considered.Equal payments at equal intervals scheme was shown to be the most profitable.Profit sharing scenarios were also considered. Inventories account for almost 50% of the total logistics costs of a supply chain. Therefore, managing inventories helps organizations to reduce costs, increase profits, and satisfy customers demand. Different inventory models have been developed to solve transportation and warehousing issues. These models help in optimizing different supply chain systems and maximizing their total profits. Coordinating orders between players has been shown to be profitable. A Consignment Stock (CS) agreement as a coordination mechanism has been receiving attention from practitioners and academicians. This paper reflects one reality of CS agreements and investigates the effects of four different payment schemes on the total profit of the system when a consignment stock agreement is adopted between a vendor and a buyer. The results showed that adopting a scheme that makes frequent and equal payments is often better than the other payment schemes compared in this paper. It was also shown in the paper that finding the optimum number and size of payments enhances the performance of the supply chain system and its total profit.

Planning tool requirements for flexible manufacturing: an analytical approach

SUMMARY The problem of tool and fixture resources dimensioning is considered and examined for a productive environment with flexible features. With reference to previous studies, different tool management strategies are pointed out and commented upon; a further control policy based on workpiece batching is suggested and tested. In the second section of the paper, an analytical interpretation of the question in hand is presented and discussed; the effectiveness of the procedure itself is tested by comparing analytical data with results derived from the detailed simulation of a real tool management area. Results are shown in the last section