Metodo Para Incrementar productividad

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2212-8271 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).Peer-review under responsibility of the scientifi c committee of The 22nd CIRP conference on Life Cycle Engineeringdoi: 10.1016/j.procir.2015.02.196

Procedia CIRP 29 ( 2015 ) 40 44

ScienceDirect

The 22nd CIRP Conference on Life Cycle Engineering

Method for increasing energy efficiency in flexible manufacturing systems: A case study

Hugo M. B. de Carvalhoa,b*, Jefferson de Oliveira Gomesb a Renault of Brazil, Av. Renault, 1300, So Jose do Pinhais, 83070-970, Brazil

b Technological Institute of Aeronautics, Praa Marechal Eduardo Gomes, 50 Vila das Accias, So Jos dos Campos, 12.228-970, Brazil

* Corresponding author. Tel.: +55 (41) 9107-1312. E-mail address: [email protected]

Abstract

In manufacturing systems, machines have been operated for years or decades without the concept of electrical energy efficiency, which has resulted in high manufacturing costs. In order to raise competitiveness by reducing energy costs, a method for systematically increasing energy efficiency is needed. This paper presents a new method to increase the energy efficiency of machine tools and equipment with computer numerical control (CNC) or a programmable logic controller (PLC). This new method was validated through application to three flexible manufacturing systems in the automotive machining industry as a case study. 2015 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the International Scientific Committee of the Conference 22nd CIRP conference on Life Cycle Engineering.

Keywords: manufacturing system; energy efficiency; electricity; energy; CNC machine tool

1. Introduction

Filippi and Ippolito [1] and Avram and Xirouchakis [2] were some of the first to study energy efficiency in machine tools with numerical control (NC). They compared data from 10 different NC machine tools involved in various operations. They concluded that the installed capacity was never fully utilized because the average power was less than half of the power available; only 60% of the total time was spent on production. Studies on the energy efficiency of flexible manufacturing systems for machining processes are necessary to define the input and output of the system in terms of useful energy. Several studies have attempted to link machining and environmental impacts. The first ones emphasising the importance of this relationship appeared in the early 1990s [3, 4]. Since then, new terms such as green machining have gained prominence in the field of computer numerical control (CNC) machine tools and manufacturing processes. Energy efficiency is achieved by streamlining useful energy. A review of recent literature shows efforts being made to increase energy efficiency in the machine tool industry. For example, Weinert et al. [5] investigated reducing the cutting

fluid used during the machining process. Rangarajan and Dornfeld [7] proposed a tool path and workpiece preparation method based on energy efficiency. Mori et al. [6] explored the monitoring of energy consumption by machine tools. Diaz et al. [8] investigated the reuse of electrical energy from a spindle. Neugebauer et al. [9] compared different drilling processes with different cutting tools and material removal rates. Suggestions to increase the energy efficiency of machining processes include turning some components of the machine off and on via NC or a programmable logic controller (PLC) [6, 10, 13], redefining the parameters of cutting tools to reduce the machining time [6, 11, 12], redefining the cutting strategy for the trajectory and path of the cutting tool [10], changing devices of low-performance machines for equipment with higher performance [10, 13], and setting machine parameters to reduce consumption (e.g. axis and spindle acceleration) [10].

For all five suggestions, examples include applications to cutting parameters, cutting strategies, and machine parameters which decrease the acceleration along the axes. Li et al. [13] showed the possibility of reducing the fixed energy consumption for different manufacturing processes for

2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).Peer-review under responsibility of the scientifi c committee of The 22nd CIRP conference on Life Cycle Engineering

41 Hugo M.B. de Carvalho and Jefferson de Oliveira Gomes / Procedia CIRP 29 ( 2015 ) 40 44

different machine states. There are examples of increasing the energy efficiency by

switching off and restarting the equipment or equipment parts during productive and non-productive times and how to implement this approach. Turning equipment on and off reduces the electrical energy consumption when the machine is in standby mode or in operation. This is true even when the equipment is responsible for a significant portion of the energy consumption of a manufacturing system. This approach has mainly focused on reducing the energy consumption of machine tools. This paper proposes a systematic method applicable not only to machine tools but also to any equipment in a manufacturing system with a PLC. The goal was to develop and apply the method to a manufacturing system. The proposed method improves on the work by Li et al. [13] to reduce the fixed power of machine tools.

1.1. Material

The electrical energy consumed by a machine is measured using measuring equipment. The measuring equipment is installed at the entrance of CNC machines and equipment. This research used the RE6000 portable power analyser (EMBRASUL) as the measuring equipment; this is shown in Fig. 1.

Fig. 1. Measuring equipment inside machining centre.

The power analyser stores data on the active power, reactive power, and effective power measured at intervals of up to hundredths of a second. Energy metering and monitoring is essential to obtaining authentic information from each individual machine, and the sample rate should be less than 0.5 s [13]. Data are stored in a file which can be transferred to a computer via a network cable. Data are obtained by a software program within the measuring equipment and later opened in a spreadsheet, as shown in Fig. 2.

After the power analyser is installed, the electrical energy consumption of each function is measured by programming the PLC. A function is a device which consumes electrical energy and executes an action. Examples include an electrical motor or electrical resistance. With the PLC, it is possible to switch the functionality of sub-components on or off to adjust the energy consumption.

Fig. 2. Electricity consumption of CNC machine tool during machining.

2. Method

For current manufacturing systems, the development of a method to increase energy efficiency is essential to minimizing the impact of the rising costs of electricity. Industries with manufacturing systems which are more than 10 years old are common. Hence, there are machines and equipment that were designed without concern for energy efficiency, which wastes electricity. In order to avoid having to invest in more energy-efficient new machinery, a systematic method was developed in this study to improve energy efficiency in manufacturing systems with new or old machinery, which is presented in Fig. 3.

Fig. 3. Method to increase energy efficiency of equipment in manufacturing system.

The first step is to measure the energy consumption of the

42 Hugo M.B. de Carvalho and Jefferson de Oliveira Gomes / Procedia CIRP 29 ( 2015 ) 40 44

equipment in the manufacturing system. After the machine or equipment is selected, the power consumption needs to be measured over a period of time, and the energy consumption and time of each step in the process need to be recorded. The energy consumption must be measured by dividing the equipment into functions. Once the functions of the equipment are defined, the next step is to analyse each function. If a function can be turned off at any time, the equipment is reprogrammed. If the function cannot be turned off at any time, it is checked to determine if the functionality can be modified in order to reduce consumption. If either of the above two conditions can be met, the functionality is turned off or modified. The equipment is measured to define the gain in energy efficiency. This cycle of analysis and reprogramming must be carried out for all equipment in a manufacturing system. It is mainly necessary for application to flexible manufacturing systems which are heavily automated. All of the reprogramming is done with the PLC or NC of the machine and must be performed by the maintenance and process engineering team. A process engineer is needed to analyse the impact of this change in the quality of the manufactured product and machine maintenance. This method also enables gains without investment because only the time spent programming the PLC or NC is required for application. This method enables the review of all functions of all equipment of a manufacturing system. Each function is measured with the measurement equipment, and the PLC of the machine is reprogrammed. Thus, each function is switched off for a new measurement. The difference is the energy consumption of the analysed function.

3. Case Study

3.1. Method to increase energy efficiency in transport equipment

As an example, this method was applied to the conveyor of different flexible manufacturing systems. The conveyor transports a piece from one operation to another in a discrete manufacturing system. However, the design of the conveyor does not provide energy efficiency. Normally, these systems remain on even without a piece to transport during production breaks or inactive periods. Each PLC controls two to five electrical motors. The measurement was performed at the entrance of the PLC. The systematic method reduced power during inactivity by approximately 1000 W. This PLC controlled two conveyors, and the method was initially applied to one conveyor. The initial consumption was measured, and the executed functions were identified. Then, the selected function was checked to verify whether or not it can be programmed to automatically turn on and off (e.g. when there is no piece entering or no manual request for the part). Finally, the electrical energy consumption of the conveyor with the programming changes was measured, as shown in Fig. 4.

Fig. 4. Method applied to conveyor in manufacturing system.

The conveyor analysed work for only 2 min per shift after the reprogramming, and the energy consumption was reduced by 90%, as shown in Fig. 5.

Fig. 5. Power consumption by conveyor after analysis and reprogramming.

3.2. Method to increase energy efficiency in machines with PLC only

The method was also applied to multiple washing machines of different flexible manufacturing systems. The method to increase energy efficiency was applied to a washing machine, and then it was replicated for another washing machine. The function of the washing machine in a manufacturing system is to clean a piece before assembly. The washing machine does not have an NC, only a PLC. The washing machine performs external washing, vacuum drying, and hot air drying, as shown in Fig. 6. The washing machine has 19 different stations with different functions, such as external washing with high pressure, internal washing with a robot, the vacuum station, and the dry hot air station. This is the reason for the high power consumption of the washing machine.

43 Hugo M.B. de Carvalho and Jefferson de Oliveira Gomes / Procedia CIRP 29 ( 2015 ) 40 44

Fig. 6. Method applied to washing machine of pieces.

The first function analysed for the washing machine was the vacuum drying. This station in the machine continues to operate throughout the process. Reprogramming the washing machine reduced consumption by 18% when there is no part to clean.

The initial measured electrical power consumption of the washing machine was 1824 Wh/cycle. After the functions of the washing machine were reprogrammed, the consumption was reduced to 1494 Wh/cycle. The vacuum drying function was reprogrammed with the PLC. When there is no part in the dry vacuum station, the washing machine turns it off. Before that, the power of the washing machine reached 200 kW during a working cycle, as shown in Fig. 7.

Fig. 7. Power consumption by part before method was applied to washing machine.

After the systematic method was applied and the PLC was reprogrammed, the maximum power reached 180 kW, as shown in Fig. 8.

Fig. 8. Power consumption by part before method was applied to washing machine.

The same methodology was applied to five different washing machines in three flexible manufacturing systems for the automotive industry. Application of the method to systematically reducing the electrical energy consumption has resulted in more than 200 actions so far.

4. Conclusion

The proposed method to systematically increase energy efficiency makes it possible to reduce power consumption during standby mode. The method reduced the electrical energy consumptions of the conveyer, washing machine, and central filter in standby mode by 83%, 12.5%, and 1% respectively. This methodology was applied to CNC machines and increased their energy efficiency. Power consumption during standby mode does not add value to the manufactured product and must be considered waste because the machine consumes energy without performing any functions or steps in the production process. If a flexible manufacturing system is in idle mode for 2 h/day for 48 productive weeks, there are 480 h/year of electricity consumption without production. These 480 h are equivalent to 20 days of 24 h production. This represents 75% of the production in 1 month for 1 year. In the literature, there has been no analysis of the energy consumption for manufacturing systems or application of a method to increase the energy efficiency of flexible manufacturing systems.

The proposed method can reduce the electrical energy consumption during non-productive and productive times through reprogramming of the PLC for any equipment. This way, the equipment can recognize when a function can be switched off without needing to know how long this situation will hold. For example, this situation may occur from the absence of a part due to failure in the previous operation.

Acknowledgements

This research is part of a PhD thesis for the Technological Institute of Aeronautics (ITA). The research was supported and carried out with the manufacturing systems at Renault of Brazil.

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