THE SEARCH FOR THE OPTIMAL NUMBER OF KANBANS IN UNSTABLE ASSEMBLY-TREE LAYOUT SYSTEMS UNDER INTENSIVE LOADING CONDITIONS

The JIT system and its operational techniques have shown noticeable advantages when applied in an ideal factory. The steadiness of demand and production times and the reduction of set-up times represent the key factor necessary in order to correctly execute JIT. Ideal environments are designed to work with smooth and stable demand patterns, constant and balanced processing times, small lot sizes and without scraps and reworks. However, these conditions are difficult to realise in real productive systems. In these contexts, the increase of operational costs, owing to the growth of inventories, necessary to match demand, often causes the failure of many JIT implementations. For these reasons, during the past years researchers have been investigating the issues related to JIT implementation in unsteady productive organisations. In this area, the kanban system, responsible for the exact propagation of information and for inventory control, is the most widely researched control mechanism. Literature proposes various kanban systems; in all cases the determination of the number of kanbans depends both on the management method chosen at each stage of the process as well as on the fluctuation of operative variables. This study deals with the problem of choosing the optimal number of kanbans in a multi-stage productive environment organised in an assembly-tree layout. In particular, this paper proposes a heuristic procedure to determine the number of kanbans and compares it with the traditional methods applied in manufacturing contexts

Otimização de uma nova unidade industrial de uma empresa na indústria da madeira

Ao longo dos últimos anos, as empresas para responderem ao mercado competitivo em que estão inseridas, necessitaram de alterar comportamentos, de modo a melhorarem e tornarem os produtos e serviços mais rentáveis. Uma das respostas a esta mudança de paradigma passa pela melhoria contínua como uma estratégia de desenvolvimento. Este projeto surge com o recente arranque de uma unidade produtora de amostras derivadas da madeira, que no passado viveu grandes períodos de pressão, mas que atualmente se encontra disposta a colmatar as falhas ocorridas durante o período de arranque. Para efeito, recorreu-se a uma metodologia de investigação qualitativa, nomeadamente a investigação ação, e procurou-se adaptar à realidade da empresa após ter sido estudado, delineado e priorizado o problema em estudo. Este trabalho propõe-se a otimizar uma pequena empresa na indústria da madeira, onde o sistema kanban e os princípios diários da melhoria contínua foram implementados. Este caso mostra como ferramentas simples motivaram a equipa a resolver os próprios problemas e ainda, como a implementação de forma integrada destas ferramentas levou à otimização da unidade.Over the past few years, companies have answered to the competitive market in which they should change behaviors to improve and make products and services more profitable. One of the answers to this paradigm shift is through continuous improvement as a development strategy. This project comes up with the recent start of a wood-derived sample-producing unit, which in the past experienced long periods of pressure, but currently is prepared to fill the gaps during the starting period. Thus, a qualitative research methodology was used, namely action research, and it was tried to adapt to the reality of the company after having been studied, delineated and prioritized the problem under study. This paper proposes to optimize a small company in the wood industry, where the kanban system and daily principles of continuous improvement have been implemented. This case shows how simple tools motivated the team to solve their own problems and, as the implementation of these tools integrated, led to the optimization of the unit.Mestrado em Engenharia e Gestão Industria

Melhoria contínua no retalho alimentar : o caso Auchan

Ao longo dos anos, com o aumento da concorrência e das exigências dos clientes, as empresas sentiram necessidade de evoluir, de forma a manterem-se competitivas e prosperarem no mercado. Para tal, tiveram de alterar as suas estratégias e adotar novos métodos de trabalho, nos quais se inclui a metodologia lean. A presente dissertação tem como principal objetivo a melhoria do desempenho da loja de Guimarães do grupo Auchan Retail Portugal - que se revê na situação apresentada -, propondo-se analisar o impacto da aplicação de processos de melhoria contínua no contexto de retalho alimentar, através da implementação de um conjunto de ferramentas lean. Para o efeito, recorreu-se à metodologia de investigação qualitativa, nomeadamente, o estudo de caso, para compreender, em detalhe e no contexto real, a dinâmica da empresa e dos seus processos. Assim, tendo como base a literatura existente sobre a metodologia lean e as suas ferramentas, foram desenvolvidos oito projetos de melhoria no terreno, divididos em cinco categorias, relativamente ao principal objetivo que pretendem responder. Cada um segue um plano de implementação baseado em cinco etapas e na aplicação de diferentes ferramentas lean, como o kanban, os 5S, o relatório A3, o diagrama de Ishikawa, o standard work, entre outros, culminando na análise aos resultados obtidos. No final, observou-se que a metodologia lean promove benefícios no desempenho de uma loja de retalho, nomeadamente, destaca-se a redução do lead time dos processos, dos custos e do stock e, em termos qualitativos, a melhoria na eficiência nos espaços de trabalho, o aumento da motivação e envolvimento dos colaboradores e o fortalecimento de uma cultura de resolução estruturada de problemas.Over the years, with increased competition and costumer requirements, companies have felt the need to evolve in order to stay competitive and thrive in the marketplace. To do this, they had to change their strategies and adopt new working methods, which include lean methodology. The main objective of this dissertation is to improve the performance of the Auchan Retail Portugal group store in Guimarães - which is reviewed in the presented situation -, proposing to analyse the impact of the application of continuous improvement processes in the food retail context, through the implementation of a set of lean tools. To that end, qualitative research methodology was used, namely the case study, to understand in detail and in real context, the dynamics of the company and its processes. Therefore, based on the existing literature on lean methodology and its tools, eight improvement projects were developed in the field, divided into five categories, in relation to the main objective they intend to respond to. Each one follows an implementation plan based on five stages and the application of different lean tools, such as Kanban, 5S, A3 report, Ishikawa diagram, standard work, among others, culminating in the analysis of the results obtained. In the end, it was observed that the lean methodology promotes benefits in the performance of a retail store, namely, the reduction of the lead time of processes, costs and stock and, in qualitative terms, the improvement in the efficiency in working spaces, the increase of the motivation and involvement of the employees and the strengthen of a problem solving structured culture

Performance analysis and development of pull-type production control strategies for evolutionary optimisation of closed-loop supply chains

The objective of this thesis is to establish a Closed-Loop Supply Chain (CLSC) design that is analysed through a series of simulation models, aimed at defining the highest performing production control strategy, whilst considering multiple related variables on both the forward and reverse flow of materials in manufacturing environments. Due to its stochastic nature, the reverse logistics side of the CLSC represents an increased source of variance for the inventory management and control strategies as it implies the erratic supply of returned materials, in addition to the very random customer demand, hence with highly variable inputs on both sides of the productive system, intrinsically inherent to this line of research. To test the operational performance of several pull-type production control strategies, a simulation-based research method was designed. The strategies experimented were: Hybrid Extended Kanban CONWIP special case (HEKC-II), Hybrid Kanban CONWIP (HKC), Dynamic Allocation Hybrid Extended Kanban CONWIP special case (DNC HEKC-II) and Dynamic Allocation Hybrid Kanban CONWIP (DNC HKC). All were tested in scenarios with high and low processing time variability and with 90% returned products and 40% returns from an open market system, therefore totaling 16 simulation models. Multi-objective evolutionary algorithms were utilised to generate the Pareto-optimum performance frontier with the objective of simultaneously minimising both performance metrics: The overall average work in progress (WIP) and the average backlog queue length (BL) for the entire CLSC. Processes used in the recovery and recycling of end of life manufactured goods were examined. This research method structures leading factors towards improved economic viability and sustainability of technologies required for the effective implementation of inventory control strategies on highly complex closed-loop supply chains with the focus on the performance metrics and optimum utilisation of resources available for the industry. The dynamic allocation strategies proved significant performance improvement, shifting the entire Pareto frontier forward with major advances on both metrics. Furthermore, it happened on all scenarios tested. The modified HEKC-II, with an optimisable parameter that enables it to be overwritten in a way that it can match the well-established HKC, also performed as originally intended and had better results than HKC in some cases, especially with the higher variability level. It also provided grounds for the suggested improvements and flexibilisation of the HEKC strategy. A major contribution of this thesis was the successful implementation of another advanced control methodology, entitled here the Intelligent Self-Designing Production Control Strategy, which provided maximum control performance. It consisted essentially of DNC HEKC-II with the following modifications: I) Extensive increase of dynamically allocated authorisation cards; II) Further anticipation of the time to trigger the change in the number of cards according to the finished goods buffer level, plus an acceleration/deceleration factor of this change; III) The capability of downsizing itself to become similar to HKC in an optimisation process if diverse production system conditions and variability would require. It displayed a very significant shift of the performance frontier