# Design Model of Flow Lines to Include Switch-Off Policies Reducing Energy Consumption
## 6 Conclusions  
A design model of flow lines to improve the efficiency of the switch-off policy has been proposed.  
The model is based on the introduction of a couple of workstations; the first is more rapid than the second in order to facilitate the switch-off of the first machine. Moreover, the proposed model allows for the evaluation of the potential benefit of energy consumption with a determined reduction in the production rate. In unbalanced flow lines, the higher idle times lead to a reduction in the total energy required for the production. However, in the idle state, stations absorb energy without working. For these reasons, applying the switch-off policy in an unbalance flow line is necessary to reduce energy consumption in the unproductive state.  
The design model is used with the discrete event simulation to highlight the energy saving with the different levels of production loss fixed. In response, our first research question asked: what is the impact of the design model proposed on the performance of the production line in terms of energy saving maximizing the production rate?  
Using the simulation, we have demonstrated that the model proposed could improve the reduction of energy consumption of the flow line more than the design model that does not consider the possibility of introducing the switch-off policy.  
However, in response to our second research question: can the constraint of a limited reduction loss improve significantly the energy saving of the production line obtaining an adequate trade off?  
Our results have demonstrated that the model can support the decision about the better trade-off between the production rate level and energy consumption reduction. Moreover, the results highlighted  
Figure 13: Pieces in buffer and mean of the work in progress.  
the better choice, if the objective is also the reduction in the number of on/off activities that can affect the maintenance of the machines. The results show that the number of warmups can be reduced by properly choosing the bottleneck position, respecting the precedence constraints, in order to achieve further energy saving.  
From a managerial viewpoint, the study was motivated by the important issue of energy consumption of flow lines. Our results suggests that: (i) the design model should be adapted to introduce the switch-off policy to obtain a higher benefit from the switch-off policies; (ii) it is possible to evaluate, with the use of the simulation, the effect of a targeted reduction of production rate (for example in a determined production planning period) to improve the energy consumption reduction; and (iii) the model proposed can be extended to different flow lines to support the decision making about the design and potential energy reduction.  
A limitation of our study is that the machines were not affected by failures and the processing times are deterministic. Machine failures have a significant impact on productivity. For this reason, integrating maintenance during scheduled machine downtime can lead to a reduction in production losses. Therefore, future works will consider the unbalance flow line design in a pull system that also considers machine failures and stochastic processing times. Furthermore, different switch-off policies, for example, that also consider demand fluctuations for shutdowns, and their effect on throughput and on energy consumption, will be investigated.  
[PERSON] performed the experiments and wrote the paper, and [PERSON] designed the experiments and revised the paper. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding  
The authors declare no conflict of interest.