Lean Assembly Supply Strategies and Results in Logistics and Manufacturing

Deployment of a lean assembly supply system has many benefits, such as productivity gains, increased cross-site communication, and planning efficiency. The article will present the theoretical basis of this application and the study of the implantation of this theory in a metal-mechanic company, as well as its impacts and results obtained. Its basic structure was adapted from the proposal of Harris, R. (2004) and Coimbra (2009) by flow with cell arrangements supported by central supermarket of manufactured and purchased parts. The study describes the steps for the implementation, the methodology used and, mainly, the difficulties in stabilizing the new process. The process uses the concepts of supermarket, line board, KLT boxes and packaging standardization, supply routes, line leveling and kaizen methodology. In the use of the new model several gains were obtained as a higher speed of supply, in relation to the ergonomic aspects, reduction of the stock in process, increase of 50% of productivity, however, some difficulties were detected that were not mapped in the initial risks of the general project . Each difficulty raised was discussed and presented to the resolution in the article, so that the structure can add knowledge in academia and organizations.A implantação de um sistema de fornecimento de montagem simples tem muitos benefícios, como ganhos de produtividade, maior comunicação entre áreas e eficiência de planejamento. O artigo apresentará a base teórica desta aplicação e o estudo da implantação desta teoria em uma empresa do ramo metalmecânico, bem como seus impactos e resultados obtidos. Sua estrutura básica foi adaptada da proposta de Harris, R. (2004) e Coimbra (2009) por fluxo com dispositivos celulares suportados pelo supermercado central de peças fabricadas e compradas. O estudo descreve os passos para a implementação, a metodologia utilizada, e especialmente as dificuldades na estabilização do novo processo. O processo utiliza os conceitos de supermercado, linha bordo, caixas KLT e padronização de embalagens, rotas de abastecimento, nivelamento de linha e metodologia de kaizen. Foram detectadas algumas dificuldades que não foram mapeadas para os riscos iniciais do projeto geral. Cada dificuldade levantada foi discutida e apresentada à resolução, mantendo o ganho apresentado no novo modelo

Transformación, cambios y renovación con visión a futuro cómo el correcto manejo de materiales en Aymesa S.A. puede ayudar a mitigar el uso innecesario de recursos

This paper discusses the current situation, operational assessment and generation of proposals regarding the handling of materials in automotive assembly company, Aymesa S.A. In first instance, the study examines the current status of operations in conjunction with the critical problems to be improved using industrial engineering tools. Based on the results, relevant time measurements are performed using simulation in order to have a baseline so a comparison of future improvement can be performed after applying the generated proposals. As a next step, operational improvements are made which after being applied may result in significant improvements potentially reducing resource use by half, especially in the process of distribution of materials, improving the use and organization of space and benefiting the materials management process for any increase in productivity.El presente trabajo de titulación trata acerca de la situación actual, evaluación operativa y generación de propuestas en cuanto al manejo de materiales en la empresa de ensamblaje automotriz Aymesa S.A. El estudio en primer término analiza el estado actual de las operaciones conjuntamente con los problemas críticos a ser mejorados utilizando herramientas de ingeniería industrial. En base a los resultados obtenidos, se realizan las mediciones de tiempo pertinentes mediante el uso de la simulación a fin de tener una línea base y así poder comparar a futuro la mejora obtenida luego de aplicar las propuestas generadas. Como paso siguiente, se proponen mejoras a nivel operativo que luego de ser aplicadas podrán resultar en mejoras significativas reduciendo potencialmente la utilización de recursos a la mitad especialmente en el proceso de distribución de materiales. Adicionalmente, se podrá mejorar la utilización y organización del espacio y beneficiando al proceso de manejo de materiales durante un eventual incremento de productividad

Evaluation of stochastic flow lines with provisioning of auxiliary material

Flow lines are often used to perform assembly operations in multi-stage processes. During these assembly operations, components that are relatively small, compared to the work pieces travelling down the flow line, are mounted to the work pieces at a given stage. Those components, or more generally, any kind of auxiliary material, are provisioned to the corresponding production stage in a repetitive but not necessarily deterministic manner using a certain delivery frequency, each time filling the local storage up to a predetermined order-up-to level. Just like random processing times, machine failures, and repairs, the randomness of the provisioning process can impact the long-term throughput of such a flow line. In this paper, we develop a fast and accurate analytical performance evaluation method to estimate the long-term throughput of a Markovian flow line of this type for the practically important case of limited buffer capacities between the production stages. We first give an exact characterization of a two-machine line of that type and show how to determine system state probabilities and aggregate performance measures. Furthermore, we show how to use this two-machine model as the building block of an approximate decomposition approach for longer flow lines. As opposed to previous decomposition approaches, even the state space of the two-machine lines can become so large that an exact solution of the Markov chains can become impractical. We hence show how to set up, train, and use an artificial neural network to replace the Markov chain solver embedded in the decomposition approach, which then leads to an accurate and extremely fast flow line evaluation tool. The proposed methodology is evaluated by a comparison with simulation results and used to characterize the structural patterns describing the behaviour of flow lines of this type. The method can be used to systematically consider the combined impact of the delivery frequency and the local order-up-to levels for the auxiliary material when designing a flow line of this type

Synchronisation of material flows in mass-customised production systems: a literature-based classification framework and industrial application

The mass customisation strategy is needed by manufacturing companies to face the increasing variety and unpredictability of products required by customers. However, mass customisation may increase the complexity of managing manufacturing and production logistics activities, for example due to reduced product batch sizes. The synchronisation of material flows within the factory is emerging as a way to address this complexity, as it enables an effective and efficient implementation of mass customisation. Indeed, the fourth Industrial Revolution introduces new digital levers, which can be combined with traditional managerial levers to achieve the synchronisation of material flows within the factory. This study contributes to the rising stream of research on this topic. A systematic literature review was conducted, leading to the development of a classification framework of the levers supporting the synchronisation of material flows. The identified managerial levers are: storage of materials, feeding policy, and scheduling. The digital levers are: materials tracking, process tracking, data analytics, and assistance systems. The developed framework was operationalised in four industrial cases and applied as a tool to map their levers related to the synchronisation of material flows

Efficient Material Flow in Mixed Model Assembly Lines

Effizienten Materialfluss im Mischmodell Montagelinien Diese Arbeit untersucht ein Materialflusssystem für Fließlinien zur Fertigung von variantenreichen Produkten. Sogenannte Routenzüge kommen häufig zur Bereitstellung von Teilen an den Arbeitsstationen einer Variantenfließlinien zum Einsatz. Die Teile werden in kleinen Behältern (Kleinladungsträgern) im Zentrallager oder in verteilten Zwischenlagern, sogenannten Supermärkten, auf den Routenzug geladen. Bei jeder Tour des Routenzugs werden mehrere Arbeitsstationen mit Kleinladungsträgern versorgt. Der zeitliche Abstand zwischen zwei Belieferungen definiert die Zugumlaufzeit. Ein derartiges Materialbereitstellungssystem, bezeichnet als In-Plant Milk Run, reduziert Bestands- und Transportkosten, weil es eine regelmäßige Just-in-Time Anlieferung der Materialien realisiert. Außerdem bringt es aufgrund der Nutzung kleiner Behälter ergonomische Vorteile mit sich. Weiterhin sinkt das Unfallrisiko. Deshalb findet das In-plant Milk Run System als Alternative zu Gabelstaplern in vielen Branchen, insbesondere in der Automobilindustrie, zunehmend Verwendung. Die Untersuchung dieser Systeme und die optimale Auswahl ihrer Parameter sind wichtige Anliegen, um die Transport- und Bestandskosten zu reduzieren. Diese Arbeit unterscheidet bei der Gestaltung von In-plant Milk Run Systemen fünf verschiedene Problemstellungen (Systeme). Für jedes System wird ein bestimmtes Planungsvorgehen zur Minimierung der kritischen Kosten vorgeschlagen. Zwischen den Systemen gibt es sowohl Ähnlichkeiten als auch Unterschiede. Die Methodik verwendet genetische Algorithmen, ganzzahlige und dynamische Programmierung, Simulation und analytische Untersuchung. Die fünf Systeme werden anhand von Kriterien klassifiziert. Als solche werden das Ausmaß von Störungen, die Verfügbarkeit der Routenzüge, die Genauigkeit der Materialbedarfsschätzungen, die Länge der Montagelinien, der mittlerer Teilebedarf und die Verfügbarkeit von technischer Infrastruktur, wie RFID- oder Barcode-Systemen, herangezogen. Unterschieden werden damit das bedarfsorientierte Zentrallager, der dezentrale bedarfsorientierte Supermarkt, das traditionelle Kanban-System, das elektronische Kanban-System und ein hybrides System, bestehend aus bedarfsorientiertem und e-Kanban-System. Dabei kann das Kanban-System sowohl im Zentrallager, als auch im System dezentraler Supermärkte zum Einsatz kommen. In bedarfsorientierten Systemen wird der Materialbedarf der Arbeitsstationen für eine gewisse Anzahl an Schichten aus der Produktionssequenz und den entsprechenden Stücklisten abgeleitet und ist damit exakt bekannt. In allen Systemen werden einige Restriktionen berücksichtigt. Hierunter fallen die Routenzugkapazität, die Dauer einer Tour und die Kapazität der Lagerflächen direkt an der Montagelinie. In jedem System sind drei Entscheidungsprobleme, das Routing, Scheduling und Loading Problem, zu lösen. Das Routing Problem beinhaltet die Zuordnung von Zügen zu Gruppen von Arbeitsstationen. Im Scheduling Problem werden die Zugumlaufzeit und der Zeitpunkt der ersten Belieferung für jeden Routenzug festgelegt. Die Lösung des Loading Problems erfordert die Determinierung von Art und Menge der in jedem Zyklus und an jede Arbeitsstation ausgelieferten Behälter. Im Falle des Vorhandenseins von Zyklen, in denen der Materialbedarf an einzelnen Arbeitsstationen die Routenzugkapazität übersteigt, werden einige Behälter vorzeitig angeliefert. Dieser Fall wird als „Early Loading“ bezeichnet und tritt in Kanban-Systemen nicht auf. Im System dezentraler bedarfsorientierter Supermärkte ist zusätzlich die Anzahl und der Standort der Supermärkte zu bestimmen („Supermarket Location Problem“). Im traditionellen Kanban-System erfolgt die Festlegung der Kanbanzahl basierend auf dem Zielkonflikt zwischen mittlerem Linienbestand und Fehlbestandswahrscheinlichkeit. Im e-Kanban-System wird der Umfang des zirkulierenden Bestands analog bestimmt. Außerdem wird ein neues Konzept, der sogenannte „Adjusted Electronic Kanban“, zur Behandlung von Kapazitätsengpässen des Routenzugs vorgestellt. Die Ergebnisse sind abhängig vom betrachteten System. Die Leistungsfähigkeit des genetischen Algorithmus zur Lösung des Supermarket Location Problems wurde anhand der Ergebnisqualität, CPU Zeit und der Variabilität dieser beiden Größen untersucht. Es wurden akzeptable CPU Zeiten und eine hohe Ergebnisqualität erreicht. Die Leistungsfähigkeit der drei Kanban-Systeme wurde unter Verwendung von Simulation getestet. Hierbei wurde die Vorteilhaftigkeit des Adjusted Electronic Kanban insbesondere im Fall begrenzter Routenzugkapazität bewiesen. Der inverse Zusammenhang zwischen mittlerem Linienbestand und Fehlbestandswahrscheinlichkeit konnte aufgezeigt werden. Im Falle der bedarfsorientierten Systeme wurde der Effekt von dynamischer Disposition, Early Loading und Minimierung der Anzahl zusätzlicher Anhänger deutlich gemacht. Bei Verwendung des hybriden Systems aus e-Kanban und bedarfsorientiertem System, liefert die dynamische Disposition in Bezug auf die Verarbeitung von Störungenerheblich bessere Resultate als die Einzelsysteme, insbesondere bei hohem Materialbedarf an den Arbeitsstationen.This study investigates the material handling system used in mixed model assembly lines which are important to produce diversified product models to satisfy the increasing customer demand. Tugger trains are used to feed by parts the workstations in the assembly lines. These parts are loaded on trains in small containers (bins) from the warehouse or intermediate stores scattered in the factory. These stores are called supermarkets, which are closer to workstations than the main warehouse. In each train tour, several workstations are replenished by bins every a certain time period called train cycle time. This replenishment system is called in-plant milk run which is used to reduce inventory and transportation costs because of its dependence on repetitive just-in-time parts delivery. Besides reducing costs, ergonomic advantages are obtained due to the use of small-sized bins. Safety hazards are also reduced. As an alternative to forklift system, in-plant milk run was used by several industries especially the automotive industry. It is important to investigate this system and to design its parameters to reduce the total material handling and inventory cost. The study divides the general problem to five different problems (systems) based on the situation on the ground. For each system, a certain planning approach is designed to optimize the parameters of the system to minimize its critical costs. There are some similarities and differences between the systems. The methodology is based on genetic algorithm, integer programming, dynamic programming, simulation, and analytical investigation. The five different systems are classified based on factors such as level of assembly line disturbances, availability of tugger trains, accuracy of expectation of workstations demand for parts, the length of assembly lines and their average demand for parts, and the availability of technical infrastructure such as radio frequency identification (RFID) or bar code technologies. These systems are main warehouse demand-oriented, decentralized supermarket demand-oriented, traditional kanban, electronic kanban, and a hybrid system of e-kanban and demand-oriented systems. The two kanban systems can be applied in both main warehouse and decentralized supermarkets systems. In demand-oriented systems, the exact workstations demand for parts is assumed to be known for the next few shifts based on the predetermined sequencing of product models and needed parts for each product model. Generally some constraints are considered in all the five systems. These constraints are tugger train capacity, tour time, and the capacity of area beside stations. There are three general problems that must be investigated in the systems. These problems are routing, scheduling, and loading problems. Routing problem is the assignment of trains to different stations. In scheduling problem, the train cycle time and the beginning of the movement of the each train are determined. In loading problem, the type and quantities of bins delivered in each train cycle to each workstation are determined. In the case that there are some peak demand periods in which the total stations demand for parts is more than the tugger trains capacity, some bins are delivered before they are needed. This case is called ‘early loading’. Early loading does not exist in both the traditional and electronic kanban systems. In decentralized supermarket demand-oriented system, the location and number of supermarkets are determined. In traditional kanban system, the number of kanban is determined based on the tradeoff between the average line-side inventory and workstation starvation. In e-kanban, the size of circulating inventory in the system is determined for the same purpose. A new approach namely, adjusted electronic kanban, is presented to accommodate train capacity problems. The results depend on the systems investigated. The performance of genetic algorithm used in supermarket location problem was tested based on the quality of the results, CPU time, and variability in both of them. Reasonable CPU time and high quality of results were obtained. The performances of e-kanban, adjusted electronic kanban, and traditional kanban were tested using simulation, where the superiority of adjusted electronic kanban was proven especially in the case of limited tugger trains capacity. The inverse relationship between the average line-side inventory and workstation starvation was presented. In the case of demand-oriented system, the effects of using dynamic scheduling, early loading, and the objective of minimizing the number of extra trailers were obvious to reduce the problems of tugger train limited capacity. In the case of using the hybrid system of e-kanban and demand-oriented systems, the dynamic planning approach outperforms the traditional systems to accommodate the line disturbances especially in the case of large workstations demand