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- Literature review on autonomous production control methodsPublication . Martins, Luis; Varela, Leonilde; Fernandes, Nuno O.; Silva, Sílvio do Carmo; Machado, JoséProduction environments are becoming more complex and dynamics. This is influenced by external factors related with products’ characteristics and costumers’ requirements and internal factors related with processing times variability, machine failures, setup times, between others. To face this increasing complexity and dynamics, it is crucial to have effective production control methods, considering Interoperability Enablers for Cyber-Physical Systems. However, production control methods most in used today, are focused on centralised decision-making and planning, and considered inadequate to deal with the increasing dynamics of these systems. Autonomous Production Control (APC) may be an adequate alternative to face this complexity, allowing flexible and rapid reaction to possible disturbances that may occur in the production system. However, as APC is the relatively new concept, there are no existing surveys. Therefore, we review and discuss the literature on APC methods to bring more attention to this promising topic of research, highlighting future research directions.
- Material flow control in make-to-stock production systems: an assessment of order generation, order release and production authorization by simulationPublication . Thürer, Matthias; Fernandes, Nuno O.; Lödding, Hermann; Stevenson, MarkMaterial Flow Control (MFC) is a key element of production planning and control. The literature typically categorizes different MFC methods according to how material flow control is realized. This distinction overlooks that MFC decisions can be subdivided into three independent tasks that are executed as orders progress through the system: (i) order generation, (ii) order release, and (iii) production authorization. MFC methods are typically designed for only one of these three tasks, which leaves a large part of the order flow uncontrolled. This study therefore not only provides a new categorization of MFC methods, but also argues for the simultaneous application (or the combining) of three different MFC methods for order generation, order release, and production authorization. To support this argument, the performance effects of an integrated MFC approach are evaluated. Findings show that each individual MFC method impacts different performance metrics, which can be explained by the presence of a hierarchy of workloads, where each workload level constrains the succeeding hierarchical level. That is, each MFC method has a main impact on a different workload. This has important implications for the design of MFC methods and extends recent literature on hierarchical production planning and control systems.
- DDMRP relative priority for production execution: an assessment by simulationPublication . Fernandes, Nuno O.; Thürer, Matthias; Silva, Sílvio do CarmoDemand-Driven Material Requirements Planning (DDMRP) was designed to improve supply chain performance in complex and uncertain environments. Literature on the topic suggests that production replenishment orders should be dispatched for execution based on the buffers’ penetration ratio of the products ordered, which is a measure of protection against stock depletion. However, the actual performance impact of this dispatching rule remains largely unknown as is the impact of different lot transfer policies. A simulation analysis was carried out to compare the performance of the lowest net flow position, the highest buffer penetration ratio, earliest operation due date and first-come first-served rules under synchronized and unsynchronized lot transfer policies. Results of our study show that the choice of dispatching rules is contingent on the setting of top-of-yellow and top-of-green, which determine the re-order quantity, and on the demand mix of products. The earliest operation due date rule shows great potential to outperform the rule typically applied in a DDMRP context specifically for a high demand mix. These findings provide important insights for improving industrial practice and for guiding future research on DDMRP.
- POLCA control in two-stage production systemsPublication . Fernandes, Nuno O.; Thürer, Matthias; Mirzaei, Nima; Ferreira, Luís Pinto; Silva, Francisco J.G.; Silva, Sílvio do CarmoPOLCA (Paired-cell Overlapping Loops of Cards with Authorization) is a decision support system for material flow control under Quick Response Manufacturing. It operates in the context of low-volume, high-mix, and cellular manufacturing. While there is an increasing literature on POLCA performance, current studies usually assume full availability of components (or parts) at assembly stations, neglecting parts manufacturing and feeding. Therefore, this study uses simulation to assess POLCA performance in a two-stage production system, where at the first stage parts are manufactured and at the second, they are assembled into end-products. The study demonstrates that using POLCA to control both production stages, manufacturing and assembly, significantly outperforms the use of POLCA at the assembly stage only, leading to important reductions of the total throughput time of orders and on the percentage of tardy orders. Statistical analysis of our results was conducted using ANOVA.
- Workload control and optimised order release: an assessment by simulationPublication . Fernandes, Nuno O.; Thürer, Matthias; Pinho, Tatiana; Torres, Pedro; Silva, Sílvio do CarmoAn important scheduling function of manufacturing systems is controlled order release. While there exists a broad literature on order release, reported release procedures typically use simple sequencing rules and greedy heuristics to determine which jobs to select for release. While this is appealing due to its simplicity, its adequateness has recently been questioned. In response, this study uses an integer linear programming model to select orders for release to the shop floor. Using simulation, we show that optimisation has the potential to improve performance compared to ‘classical’ release based on pool sequencing rules. However, in order to also outperform more powerful pool sequencing rules, load balancing and timing must be considered at release. Existing optimisation-based release methods emphasise load balancing in periods when jobs are on time. In line with recent advances in Workload Control theory, we show that a better percentage tardy performance can be achieved by only emphasising load balancing when many jobs are urgent. However, counterintuitively, emphasising urgency in underload periods leads to higher mean tardiness. Compared to previous literature we further highlight that continuous optimisation-based release outperforms periodic optimisation-based release. This has important implications on how optimised-based release should be designed.
- Planeamento e controlo da produção em ambientes dinâmicos : DDMRPPublication . Fernandes, Nuno O.; Silva, Sílvio do CarmoFlexibilidade, eficiência e eficácia ao nível da atividade produtiva são importantes vantagens competitivas para as empresas industriais responderem à volatilidade dos mercados atuais. Os sistemas tradicionais de Planeamento e Controlo da Produção, ainda largamente usados na indústria, não foram desenvolvidos para operar adequadamente neste contexto. A abordagem recentemente proposta, conhecida como Demand-Driven Material Requirements Planning (DDMRP) pode ser vista como um instrumento de Planeamento e Controlo da Produção capaz de responder aos objetivos de flexibilidade, eficiência e eficácia requeridos no contexto atual de produção e procura de bens.
- A simulation study of aircraft boarding strategiesPublication . Moreira, Hélio; Ferreira, Luís Pinto; Fernandes, Nuno O.; Silva, Francisco J.G.; Ramos, Ana L.; Ávila, PauloTo ensure the safety of passengers concerning virus propagation, such as COVID-19, and keep the turnaround time at low levels, airlines should seek efficient aircraft boarding strategies in terms of both physical distancing and boarding times. This study seeks to analyze the impact of different boarding strategies in the context of the International Air Transport Association’s recommendations during the pandemic to reduce interference and physical contact between passengers in airplanes. Boarding strategies such as back-to-front, outside-in, reverse pyramid, blocks, Steffen, and modified optimal have been tested in this context. This study extends the previous literature using discrete event simulation to evaluate the impact of the occupation of the middle seat by family members only. This study also analyses the impact of having passengers carrying hand luggage and priority passengers on the performance of these strategies concerning boarding times. In general, the simulation results revealed a 15% improvement in boarding times when the reverse pyramid strategy is used compared to a random strategy, which essentially results from a reduction in the boarding interferences between passengers. The results also show that Steffen’s strategy is the best performing, while the blocks strategy results in the worst performance. This study has practical implications for airline companies concerning both operation efficiency and passenger safety.
- Industry 4.0 in the automotive sector: development of a decision support tool for car dealerships using simulationPublication . Bessa, Ruben; Ferreira, Luís Pinto; Fernandes, Nuno O.; Ávila, Paulo; Ramos, Ana L.The concept of Industry 4.0 promises to transversally revolutionise industries. Simulation, as one of the main pillars of Industry 4.0, allows improvements in the organisational and production processes of companies. This research work develops a decision support tool based on system dynamics, that address the problem of car dealership sales forecast and evolution depending on the commercial strategies adopted. This decision support tool considers main variables that are expected to influence car sales in Portugal. To develop this tool several interviews were conducted with the people responsible for the commercial sector of different dealerships while considering existing literature on the subject. This allowed us to parameterize a system dynamics model with the most influential sales factors. The developed tool is expected to contribute to car dealerships to evaluate their commercial policies and define adjustments to these to improve profitability.
- Lean manufacturing applied to a wiring production processPublication . Pena, R.; Ferreira, Luís Pinto; Silva, F.J.G.; Sá, J.C.; Fernandes, Nuno O.; Pereira, T.This project was carried out at a company in the electric mobility sector, which manufactures chargers for electric vehicles, specifically in the wiring section. The main objective of the developed work was to improve the production processes in order to enhance responsiveness to the growing demand. After analyzing the processes in the section, the objectives were outlined to enable the improvement of some practices in the production department, such as the ones related to the organization of the raw material supermarket, as well as the calculation of the wiring consumption by chargers, and the implementation of a production control system. After the improvement actions were implemented, it was possible to observe a 14,9% reduction in the changeover process of the cable cutting process; weekly wiring consumptions were estimated, and procedures were defined to generate orders of raw material and supply to the workstation, which led to the elimination of stock shortages. In addition, worker autonomy increased and production downtime was reduced.
- Analysis and improvement of the packaging sector of an industrial companyPublication . Alves, Diogo; Ferreira, Luís Pinto; Pereira, T.; Sá, J.C.; Silva, F.J.G.; Fernandes, Nuno O.Manual operations in manufacturing companies are still a common practice. This often results in high costs, high cycle times and therefore in lower productivity, particularly for companies operating in western countries. This is why many manufacturing companies relocated their production facilities in low age countries. This study was developed at a leading Portuguese material construction manufacturing company. The objective was to improve the packaging and labeling processes, that were identified as main bottlenecks in the factory. Lean was used to streamline these processes before being automated. This allowed for annual savings of 12432 €, with human operators being reallocated to other departments where they are more useful. Furthermore, cycle times were reduced by 42,9%, non-value-added activities were minimized, and operations with potentially high ergonomic risks were eliminated. In addition, a reduction of 84,3% in lithographed packaging was achieved, with a cost reduction of around 36 000 €/year, which is expected to continue in the forthcoming years.