ABSTRACT This study puts forward a multi-attribute decision model that determines good production and inventory parameter settings in make-to-stock (MTS) environments controlled by the Conwip (constant work-in-process) method. This model uses a discrete event simulation to evaluate the performance of a system in relation to work-in-process and a finished goods inventory. Based on Multi-Attribute Value Theory (MAVT), a compromise solution is found by taking into account the decision-maker’s preferences and tradeoff judgments as to the attributes of cycle time, throughput rate, holding cost and stockout cost. A numerical application is given to illustrate the use of the proposed multi-attribute model which includes a sensitivity analysis.

This paper proposes a method for defining the levels of work in progress (WIP) in productive environments managed by constant work in process (CONWIP) policies. The proposed method combines the approaches of Computer Simulation and Electre TRI to support estimation of the adequate level of WIP and is presented in eighteen steps. The paper also presents an application example, performed on a metalworking company. The research method is based on Computer Simulation, supported by quantitative data analysis. The main contribution of the paper is its provision of a structured way to define inventories according to demand. With this method, the authors hope to contribute to the establishment of better capacity plans in production environments.

Este estudo apresenta uma reflexão teórica a respeito dos possíveis impactos nos indicadores da Teoria das Restrições (TOC) provocados pelas Sete Perdas abordadas no Sistema Toyota de Produção (STP) e por um tipo de perda não relatada neste contexto. Trata-se da 'Perda por má definição do mix de produtos' influenciada pelo uso de métodos inadequados para formular o mix de produtos. Desta forma é construído um neologismo conceitual identificado como as 'Pergas' para demostrar as perdas de Ganho global (TOC), derivadas desta prática. A necessidade de combater as perdas nos processos deve-se a não agregação de valor ao produto, bem como a geração de custos, motivando, em algumas situações, o compromentimento à competitividade da organização. Em sentido similar, o combate às Pergas proporciona um incremento nos índices monitorados pelos indicadores Globais da TOC por meio da constiuição de um mix de produtos que contribua com a meta da empresa. Um referencial estrutural é desenvolvido relacionando as Sete Perdas abordadas no STP e os indicadores da TOC, o qual fornecerá subsídios para fundamentar as relações impactantes e possibilitará a proposição de ações de melhoria tendo por objetivo minimizar os impactos apresentados.

This study presents a theoretical reflection about the possible impacts on of the Theory of Constraints (TOC) indicators caused by the Seven Wastes in the Toyota Production System (TPS) and a type of waste which is not included in that context. It refers to the 'waste due to unsatisfactory definition of product mix' influenced by the use of inappropriate methods to formulate the product mix. Therefore, a conceptual neologism is introduced, identified as the "Pergas" to demonstrate the overall gain waste derived from this practice. The need to reduce process waste is due to the fact that no value is added to the product and the cost increase putting at risk, in some situations, the organizational competitiveness. Similarly, the fight against "Pergas" leads to an increase in the indexes monitored by the Global indicators of TOC, through the creation of a mix of products that contributes to the company's goal. A structural framework was developed relating the seven Wastes addressed in the TPS and TOC indicators, which will provide subsidies to support the relations that cause impacts and will enable the proposal of improvement actions focusing on reducing the impacts presented.