A New Multicommodity Flow Model for the Job Sequencing and Tool Switching Problem

Artigo científico.In this paper a new multicommodity flow mathematical model for the Job Sequencing and Tool Switching Problem (SSP) is presented. The proposed model has a LP relaxation lower bound equal to the number of tools minus the tool machine’s capacity. Computational tests were performed comparing the new model with the models of the literature. The proposed model performed better, both in execution time and in the number of instances solved to optimality.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

Supplier Ranking System and Its Effect on the Reliability of the Supply Chain

Today, due to the growing use of social media and an increase in the number of A HITS with a solution in PageRank (Massimo, 2011) sharing their opinions globally, customers can review products and services in many novel ways. However, since most reviewers lack in-depth technical knowledge, the true picture concerning product quality remains unclear. Furthermore, although product defects may come from the supplier side, making it responsible for repair cost, it is ultimately the manufacturer whose name is damaged when such defects are revealed. In this context, we need to revisit the cost vs. quality equations. Observations of customer behavior towards brand name and reputation suggest that, contrary to the currently dominant model in production where manufacturers are expected to control only Tier 1 supplier and make it responsible for all higher tiers, manufacturers should also have a better hold on the entire supply chain. Said differently, while the current system considers all parts in Tier 1 as equally important, it underestimates the importance of the impact of each piece on the final product. Another flaw of the current system is that, by commonizing the pieces in several different products, such as different care models of the same manufacturer to reduce the cost, only the supplier of the most common parts will be considered essential and thus get the most attention during quality control. To address the aforementioned concerns, in the present study, we created a parts/supplier ranking algorithm and implemented it into our supply chain system. Upon ranking all suppliers and parts, we calculated the minimum number of the elements, from Tier 1 to Tier 4, that have to be checked in our supply chain. In doing so, we prioritized keeping the cost as low as possible with most inferior possible defects

Improved heuristic algorithms for the job sequencing and tool switching problem.

In flexible manufacturing systems, a single machine can be configured with different tools for process- ing different jobs, each requiring a specific set of tools. There is a limit to the maximum number of tools that can be loaded simultaneously in the machine; between the processing of two different jobs, it may be necessary to switch these tools, causing interruptions in the production line. The Job Sequenc- ing and Tool Switching Problem (SSP) aims to determine a job sequence and the tool-loading order for a flexible machine, in order to minimize the number of tool switches. These two tasks can be separated into Sequencing , an N P -hard problem, and Tooling , which is a Pproblem if the job sequence is given. This paper proposes a methodology that uses graph representations, heuristic methods, and local search methods to solve the sequencing problem. These contributions are combined in an Iterated Local Search scheme, which is then combined with a classical tooling method, in order to solve the SSP. Comprehen- sive computational experiments show that the resulting method is competitive and can establish new best solutions for literature instances, while outperforming the current state-of-the-art method

Novas formulações de fluxo para problemas de otimização combinatória

Neste trabalho aborda-se o Problema de Minimização de Trocas de Ferramentas (PMTF) e o Problema do Caixeiro Viajante Multiproduto com Prioridades (PCVMP). O PMTF consiste em determinar um sequenciamento de tarefas, de tal modo que a quantidade de trocas de ferramentas entre as tarefas seja a menor possível. Cada tarefa requer um conjunto de ferramentas distinto, e supõe-se que cada um destes conjuntos não contenha mais ferramentas do que suporta a máquina. Já o PCVMP consiste em determinar uma rota de entrega de mercadorias considerando ao mesmo tempo, o cliente e o vendedor, ou seja, minimizando os custos totais do vendedor e maximizando as preferências dos clientes. Neste estudo tem-se como objetivo modelar, baseado em fluxo multicommodity, os problemas citados. Modelos matemáticos de otimização foram propostos assim como alguns resultados teóricos foram desenvolvidos. No caso do PMTF, o melhor modelo proposto foi comparado com os modelos existentes na literatura, mostrando um melhor desempenho tanto em quantidade de instâncias resolvidas na otimalidade, quanto no valor da relaxação linear e no tempo de execução. Mostrou-se que o valor da relaxação linear nos modelos propostos corresponde a diferença entre a quantidade de ferramentas e a capacidade da máquina. Algumas matheurísticas baseadas em busca por proximidade e um método exato enumerativo considerando eliminação de simetria foram propostos e comparados com os resultados da literatura. Já no caso do PCVMP, o modelo proposto se mostrou eficiente em resolver instâncias de pequeno e médio porte. Duas metaheurísticas, BRKGA e BRKGA adaptativo, ambas com busca local, também foram propostas para o PCVMP, apresentando bons resultados.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES