La gestione del livello di buffer per la programmazione operativa in processi a ciclo non definito

Viene affrontato il problema della programmazione operativa con riferimento a processi produttivi per i quali non riesce possibile disporre fin dall’inizio di tutte le informazioni al riguardo necessarie. In tali processi (a ciclo non definito) le specifiche del prodotto, non determinate a priori, possono anche mutare in corso di lavorazione, ciò che impedisce l’impiego efficace di sistemi tradizionali di planning. In precedenza, trattando la stessa casistica, si era scelto di utilizzare un modello statistico appositamente sviluppato per determinare la configurazione probabile dei cicli di lavorazione, impiegato per calcolare un valore atteso del grado di utilizzazione delle risorse di produzione ed individuare possibili colli di bottiglia. In questa sede ci proponiamo inoltre di sincronizzare il flusso produttivo agendo sul time buffer posto a protezione della risorsa critica, come sopra individuata. La dimensione ottima del buffer è determinata attraverso il trade-off tra il vantaggio di un’idonea saturazione dell’anzidetta risorsa critica ed il costo alternativo della coda in attesa. Ciò vale a definire efficaci regole di rilascio dei job per le stazioni di lavoro a monte. Il monitoraggio del buffer è necessario inoltre per aggiornare la programmazione al variare delle condizioni operative. L’efficacia del criterio proposto è stata verificata dagli stessi autori attraverso diretta applicazione presso un’azienda operante nel settore della revisione di motori aeronautici. I risultati ottenuti si sono rivelati più che soddisfacenti in ordine al migliore sfruttamento delle risorse produttive nonché in termini di abbattimento del work in process

Criterio di ottimizzazione della dotazione primaria ricambi nell’industria cantieristica

Ai fini delle specifiche scelte di primo equipaggiamento si prende in considerazione il problema dell’assortimento ottimale della scorta ricambi da costituire a corredo base di una unità tanker, opportunamente caratterizzata attraverso specifici parametri dimensionali e funzionali . L’attenzione riservata al problema in esame è motivata dalla peculiarità intrinseca al prodotto dell’industria cantieristica, in vista delle condizioni cui è sottoposto in esercizio e delle prestazioni cui è chiamato nel corso della sua vita utile. In tal senso si riscontra l’improprietà di affrontare il problema ricorrendo ad approcci che possono riuscire validi in altro ambito applicativo. Il criterio in questa sede prospettato, manifestamente orientato a soddisfare fondamentali requisiti di sicurezza e affidabilità, al tempo stesso tiene conto dell’imprescindibile limite di budget destinato alla scorta ricambi, nonché della frequenza con cui vengono effettuati gli interventi manutentivi per il sistema in esame. Utilizzando un opportuno indice di criticità dei ricambi, lo studio è stato sviluppato in modo del tutto originale con l’impiego di efficaci strumenti di ricerca operativa. La validità dei risultati conseguiti trae riscontro dall’interesse al riguardo manifestato da una primaria industria cantieristica, che con gli autori è coinvolta in un progetto di ricerca di respiro pluriennale, finalizzato ad accrescere l’efficienza dei servizi manutenzione offerti alle compagnie di navigazione

Simplifying the Virtual Safety Stock formula

The paper deepen the analysis into the Virtual Safety Stock theory, which is an approach intended to drastically reduce safety inventory levels exploiting the eventual time lag between the moment when a product is ordered and the time the product needs to be available, while preserving the same performance as a production system that operates with physical safety stock. The original virtual safety stock definition embeds two major problems: a double Gaussian integral in the formulation together with the heritage of the unrealistic assumptions already included in the earliest Hadley and Whitin’s safety stock conception. This paper describes an alternative approach in which the virtual safety stock is defined with a closed-form expression much easier to compute and use in operations management practice

Dynamic management model for offhire movements of a carrier fleet

This paper presents an innovative dynamic route management model for direct on-demand transportation services. In these scenarios, a carrier is hired for a transportation service from an origin to a destination point and then released. Subsequently, being in the off-hire condition, the carrier can wait in the destination point or move towards another loading dock. The aim of the approach is to identify the best route and the optimal waiting strategy of the carrier while in the off-hire condition, minimizing the dead-head movement costs and maximizing the expected profit originating from the forecasted demand. This model has been tested in the industry of the oil tankers fleet. So far this problem has been partially fronted with models which are focused on the evaluation of each loading dock profitability, lacking however to consider the opportunity of a continuous-moves routing in the off-hire condition. This analysis defines instead a dynamic strategy which estimates the future demand and is continuously updated by the other carriers movements and by the variation in the scenario. A set of Deviation Points and Waiting Areas are identified respectively as alternatives for the carrier off-hire movements and as areas in which the carrier has the possibility to stop and wait for a new order. These points are determined on a geographical map on behalf of statistical and economical considerations. Time constraints are also considered, especially in terms of Time Windows in which the carrier has to react to the demand and to reach the origin of the order

Integrating MRP in production systems simulation tools

Literature review suggests concentrating on the development of new reference model for manufacturing system simulation, which may implement an operation logic much closer to real industrial contexts. A production system modelling tool should be designed with the aim of standardizing and simplifying the simulation of manufacturing processes and to widespread this approach in SMEs. With this aim, the authors got committed in designing a reference model for providing a structural framework to support shop-floor simulation and optimization. This paper presents the basic framework logic and structure of the simulation tool, showing how it is possible to represent it in Business Process Modelling Notation (BPMN). On top of this, the efforts of implementing an MRP module on top of a simulation took which was originally conceived to embed look-back material handling policies area described, together with the operative solutions chosen to reach the integration

A complexity analysis model for management of Good Manufacturing Practice and ISO 9000-2001 compliancy simultaneous projects. Case study in the pharmaceutical industry

Quality improvement is definitively one of the major leading forces nowadays. In the manufacturing industry, the globalisation trend forces companies to modify their processes in order to comply to specific quality regulations. In pharmaceutical industry, the FDA Good Manufacturing Practices (GMPs) represent a landmark in defining the Quality Product, which is a complex multifaceted concept (“In conformity with identity, purity, physical shape and stability requirements” Code of Federal Regulations, 2000). Even if the FDA regulation has been defined for U.S. market, lots of European companies are starting to implement GMPs compliancy projects. The European UNI EN ISO 9000-2001 regulation concentrates anyway on Quality Assurance, which is defined as a mean to make stakeholders confident about compliancy to their requirements. ISO 9000-2001 and GMPs regulations are neither in antithesis nor in alternative, but are complementary; pharmaceutical companies are now persuaded that Quality Assurance is a strategic objective as well as Quality Product, to be pursued by process optimisation and by production planning and control. Any modification in the process structure of an industrial plant in order to meet the requirement of a quality regulation requires a deep commitment and big expenditures; when the aim is the complete compliancy to two main regulations such as US GMPs and EU ISO 9000-2001 the project management is definitively critical. This paper aims to develop a project evaluation and management model for a program of plant adaptation to meet simultaneously both GMPs and ISO 9000-2001 standards; such model is based on a complexity analysis procedure for process modification and updating, and it is focused on the exploitation of the potential synergies among the adaptation project activities. The proposed model is divided in three main phases: firstly, quality requirements are disaggregated according to relevant operative areas, in order to outline adaptation activities characteristics. Then, the second phase aims to estimate the impact on each operative area performance of the relative adaptation activities; for this purpose, activities complexity is evaluated using specific indicators and weighted through cost elements. Finally, the model concludes with gap analysis procedure which is used to plan a coordinated and optimised simultaneous adaptation project management. The model has been tested in a pharmaceutical company that was already GMPs compliance since ’90 and during 2000 was adapting its production process for a GMPs review and for the first ISO external audit. We applied our proposal to both the adaptation projects and we succeeded in obtaining important confirmation about achievable benefits in terms of reducing costs and activities balancing

Substituting stock with time: the effect of delivery spare time on safety stock

The aim of this paper is to explore some operative aspects of virtual safety stock management and specifically how the parameters of the traditional safety stock management model could be modified when the delivery due dates do no impose binding constraint on the production or the delivery pace. The presence of an extra-time for the delivery can be exploited to decrease the safety stock and/or to increase service level indeed. The analysis has been carried out in the most general case in which safety stock is kept in order to protect from both the variability of the demand and the variability of supplier delivery lead times

La gestione del livello di buffer per la programmazione operativa in processi a ciclo non definito

Viene affrontato il problema della programmazione operativa con riferimento a processi produttivi per i quali non riesce possibile disporre fin dall’inizio di tutte le informazioni al riguardo necessarie. In tali processi (a ciclo non definito) le specifiche del prodotto, non determinate a priori, possono anche mutare in corso di lavorazione, ciò che impedisce l’impiego efficace di sistemi tradizionali di planning. In precedenza, trattando la stessa casistica, si era scelto di utilizzare un modello statistico appositamente sviluppato per determinare la configurazione probabile dei cicli di lavorazione, impiegato per calcolare un valore atteso del grado di utilizzazione delle risorse di produzione ed individuare possibili colli di bottiglia. In questa sede ci proponiamo inoltre di sincronizzare il flusso produttivo agendo sul time buffer posto a protezione della risorsa critica, come sopra individuata. La dimensione ottima del buffer è determinata attraverso il trade-off tra il vantaggio di un’idonea saturazione dell’anzidetta risorsa critica ed il costo alternativo della coda in attesa. Ciò vale a definire efficaci regole di rilascio dei job per le stazioni di lavoro a monte. Il monitoraggio del buffer è necessario inoltre per aggiornare la programmazione al variare delle condizioni operative. L’efficacia del criterio proposto è stata verificata dagli stessi autori attraverso diretta applicazione presso un’azienda operante nel settore della revisione di motori aeronautici. I risultati ottenuti si sono rivelati più che soddisfacenti in ordine al migliore sfruttamento delle risorse produttive nonché in termini di abbattimento del work in process

Substituting stock with time: the effect of delivery spare time on safety stock

The aim of this paper is to explore some operative aspects of virtual safety stock management and specifically how the parameters of the traditional safety stock management model could be modified when the delivery due dates do no impose binding constraint on the production or the delivery pace. The presence of an extra-time for the delivery can be exploited to decrease the safety stock and/or to increase service level indeed. The analysis has been carried out in the most general case in which safety stock is kept in order to protect from both the variability of the demand and the variability of supplier delivery lead times

Dynamic management model for offhire movements of a carrier fleet

This paper presents an innovative dynamic route management model for direct on-demand transportation services. In these scenarios, a carrier is hired for a transportation service from an origin to a destination point and then released. Subsequently, being in the off-hire condition, the carrier can wait in the destination point or move towards another loading dock. The aim of the approach is to identify the best route and the optimal waiting strategy of the carrier while in the off-hire condition, minimizing the dead-head movement costs and maximizing the expected profit originating from the forecasted demand. This model has been tested in the industry of the oil tankers fleet. So far this problem has been partially fronted with models which are focused on the evaluation of each loading dock profitability, lacking however to consider the opportunity of a continuous-moves routing in the off-hire condition. This analysis defines instead a dynamic strategy which estimates the future demand and is continuously updated by the other carriers movements and by the variation in the scenario. A set of Deviation Points and Waiting Areas are identified respectively as alternatives for the carrier off-hire movements and as areas in which the carrier has the possibility to stop and wait for a new order. These points are determined on a geographical map on behalf of statistical and economical considerations. Time constraints are also considered, especially in terms of Time Windows in which the carrier has to react to the demand and to reach the origin of the order