Method for increasing energy efficiency in flexible manufacturing systems

Available online at 2212-8271 © 2015 The Authors. Published by Elsevier B.V . This is an open access article under the CC BY-NC-ND license (/licenses/by-nc-nd/4.0/).Peer-review under responsibility of the scientifi c committee of The 22nd CIRP conference on Life Cycle Engineering doi: 10.1016/j.procir.2015.02.196P rocedia CIRP 29 ( 2015 )40 – 44ScienceDirectThe 22nd CIRP Conference on Life Cycle EngineeringMethod for increasing energy efficiency in flexible manufacturing systems:A case studyHugo M. B. de Carvalho a,b *, Jefferson de Oliveira Gomes baRenault of Brazil, Av. Renault, 1300, São Jose do Pinhais, 83070-970, BrazilbTechnological Institute of Aeronautics, Praça Marechal Eduardo Gomes, 50 – Vila das Acácias, São José dos Campos, 12.228-970, Brazil* Corresponding author. Tel.: +55 (41) 9107-1312. E-mail address: hugombc@AbstractIn 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 responsibili ty of the International Scientific Committee of the Conference “22nd CIRP conference on Life Cycle Engineering. Keywords: manufacturing system; energy efficiency; electricity; energy; CNC machine tool1. IntroductionFilippi 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 (/licenses/by-nc-nd/4.0/).Peer-review under responsibility of the scientifi c committee of The 22nd CIRP conference on Life Cycle Engineering41H ugo M.B. de Carvalho and Jefferson de Oliveira Gomes / P rocedia CIRP 29 ( 2015 )40 – 44different machine states.There are examples of increasing the energy efficiency byswitching off and restarting the equipment or equipment partsduring productive and non-productive times and how toimplement this approach. Turning equipment on and offreduces the electrical energy consumption when the machineis in standby mode or in operation. This is true even when theequipment is responsible for a significant portion of theenergy consumption of a manufacturing system. Thisapproach has mainly focused on reducing the energyconsumption of machine tools. This paper proposes asystematic method applicable not only to machine tools butalso to any equipment in a manufacturing system with a PLC.The goal was to develop and apply the method to amanufacturing system. The proposed method improves on the work by Li et al. [13] to reduce the fixed power of machine tools.1.1.MaterialThe 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 than0.5 s [13]. Data are stored in a file which can be transferred toa 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.MethodFor 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 the42H ugo M.B. de Carvalho and Jefferson de Oliveira Gomes / P rocedia CIRP 29 ( 2015 )40 – 44 equipment in the manufacturing system. After the machine orequipment is selected, the power consumption needs to bemeasured over a period of time, and the energy consumptionand time of each step in the process need to be recorded. Theenergy consumption must be measured by dividing theequipment into functions. Once the functions of theequipment are defined, the next step is to analyse eachfunction. If a function can be turned off at any time, theequipment is reprogrammed. If the function cannot be turnedoff at any time, it is checked to determine if the functionalitycan be modified in order to reduce consumption. If either ofthe above two conditions can be met, the functionality isturned off or modified. The equipment is measured to definethe gain in energy efficiency. This cycle of analysis andreprogramming must be carried out for all equipment in amanufacturing system. It is mainly necessary for applicationto flexible manufacturing systems which are heavilyautomated. All of the reprogramming is done with the PLC orNC of the machine and must be performed by themaintenance and process engineering team. A processengineer 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 Study3.1.Method to increase energy efficiency in transport equipmentAs 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 onlyThe 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 washingmachine.43 H ugo M.B. de Carvalho and Jefferson de Oliveira Gomes / P rocedia CIRP 29 ( 2015 )40 – 44Fig. 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.ConclusionThe 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. AcknowledgementsThis 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 ofBrazil.44H ugo M.B. de Carvalho and Jefferson de Oliveira Gomes / P rocedia CIRP 29 ( 2015 )40 – 44References[1] Filippi AD, Ippolito R. NC machine tools as electrical energy users. Annof the CIRP 1981; 30(1): 323-6.[2] Avram OI, Xirouchakis P. Evaluating the use phase energy requirementsof a machine tool system. J Clean Prod 2011; 19(6-7): 699-711.[3] Byrne G, Scholta E. Environmentally clean machining processes –Astrategic approach. Ann of the CIRP 1993; 42(1): 471-4.[4] Gonzalez A. Machine tool utilisation phase: costs and environmentalimpacts with a life cycle view. 82f. Thesis (Master of Science).Stockholm: Royal Institute of Technology; 2007. /smash/get/diva2:411777/FULLTEXT01.pdf. Accessed: 25 Sep.2014.[5] Weinert K,Inasaki, I., Sutherland, JW., Wakabayashi, T., Dry machiningand minimum quantity lubrication. CIRP Ann –Manuf Technol 2004;53(2): 511-37.[6] Mori M, Fujishima M, Inamasu Y, Oda Y. A study on energy efficiencyimprovement for machine tools. CIRP Ann –Manuf Technol 2011; 60: 145-8.[7] Rangarajan A, Dornfeld D. Efficient tool paths and part orientation forface milling. CIRP Ann 2004; 53(1): 73-6. [8] Diaz N, Choi S, Helu M, Chen Y, Jayanathan S, Yasui Y, Kong D,Pavanaskar S, Dornfeld D. Machine tool design and operation strategies for green manufacturing. CIRP HPC 2010; 1: 271-6.[9] Neugebauer R, Wertheim R, Hochmuth C, Schmidt G, Dix M, Modellingof energy and resource-efficient machining. 4th CIRP HPC 2010; 1: 295-300.[10] Dietmair A, Verl A, Eberspaecher P. Predictive simulation for modelbased energy consumption optimisation in manufacturing system and machine control. Teesside, UK: FAIM, 2009.[11] Mativenga PT, Rajemi MF. Calculation of optimum cutting parametersbased on minimum energy footprint. CIRP Ann – Manuf Technol 2011;60: 149–52.[12] Balogun VA, Mativenga PT. Modelling of direct energy requirements inmechanical machining processes. J Clean Prod 2013; 41: 179-186. [13] Li W, Zein A, Kara S, Herrmann C. An investigation into fixed energyconsumption of machine tools. In: Hesselbach J, Herrmann C, editors.Globalized solutions for sustainability in manufacturing. Braunschweig, Germany: Springer-Verlag Berlin Heidelberg; 2011. p. 268-73.。