To improve productivity and energy efficiency, attention has been paid to practical methods to evaluate productivity and energy consumption in actual manufacturing processes. In the plastics industry, the injection molding machine is one of the common production machines for manufacturing plastic parts. It consumes a large amount of energy due to having injection molding processes such as melting the material. In addition, a production line including the injection molding machine generally has various auxiliary machines to improve productivity and maintain product quality. Since the states of each machine in the production line change based on production situations, the behavior of energy consumption in the production line becomes more complicated. Therefore, it is difficult to evaluate energy consumption in the production line while grasping dynamically changing the states of each machine. This paper proposes a simulation system that simultaneously evaluates productivity and energy consumption in the production lines including the injection molding machine for design and improvement of production line. To simulate productivity and energy consumption, we develop a state transition model in the production line. This model defines the interrelationship between state transitions and their sequence among the machines. Furthermore, by making a correlation between the machine state and its energy consumption, the state transition model enables to calculate energy consumption in various production scenarios. By implementing the state transition model in a discrete-event simulation, it is possible to evaluate the indicators of productivity and energy consumption such as throughput and specific energy consumption. To verify the effectiveness of the proposed simulation system, we show a case study of productivity and energy consumption when designing a new production line including an injection molding machine. The results show that we obtain the evaluation indicators of productivity and energy consumption regarding various production lines.
Methods for evaluating productivity and energy consumption simultaneously have been getting significant interest in the industry. In particular, although injection molding machines are important system components for production in plastic molding, a method for simultaneously evaluating their productivity and energy consumption has not been established. Therefore, we propose a simulation method that is based on a state transition model containing state transitions and states of machines in an injection molding production line.
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