1-IJAEST-Volume-No-2-Issue-No-2-Analysis-on-the-Influence-of-the-Number-of-Pallets-Circulating-on-an by ISERP ISERP

Luís Pinto Ferreira et al. / (IJAEST) INTERNATIONAL JOURNAL OF ADVANCED ENGINEERING SCIENCES AND TECHNOLOGIES Vol No. 2, Issue No. 2, 119 - 123

Analysis on the Influence of the Number of Pallets Circulating on an Automobile Closed-Loops Assembly Line Escola Superior de Estudos Industriais e de Gestão Instituto Politécnico do Porto Vila do Conde, Portugal Luispintoferreira@eu.ipp.pt

A simulation model in an Arena environment was developed, based on a real case, which allowed the analysis of aspects which have still not been studied in specialized literature, namely the assessment of the impact of the number of pallets, circulating on the first three closed loops, on the number of automobiles produced. In order to obtain the functions that describe the behaviour of the assembly system, the design of an experiment technique was used.

Keywords-

Lines;

Simulation;

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Automobile Assembly Closed-Loops; Manufacturing.

INTRODUCTION

At present, due to the globalisation process which the industrial world is experiencing, companies are faced with the challenge of continuously improving their productivity, responding efficiently and quickly to the market’s requirements [1, 2]. As a result, production and its ensuing performance have become increasingly important, especially in the highly technological sectors [3]. The automobile production line is an example of this since it includes a great deal of automation. In order to improve its performance and optimization, simulation was used as a decision-making support tool. According to [4], simulation constitutes an efficient tool in the analysis of production line behaviour, especially when analytical methods prove to be difficult to apply. In practice, computer simulation is one of the most commonly used operational research tools; it allows the projection and analysis of the performance of complex systems and processes [5], by imitating their dynamic

ISSN: 2230-7818

Área Ingeniería de los Procesos de Fabricación Universidad de Vigo Vigo, Spain 1 enrares@uvigo.es, 2gupelaez@uvigo.es, 3 marina.salgado@uvigo.es, 4jdieguez@uvigo.es behaviour [6]. Simulation involves the representation of a real system in a computer-developed model by using an appropriate simulation language [4, 7]. For [8], the concept of simulation is related to a vast range of methods and applications, which imitate the behaviour of real systems, usually by means of appropriate computer software. In fact, for these authors, simulation is an extremely generic term because the underlying idea can be used in various sectors, industries and applications. An identical opinion is expressed by [9], who adds that simulation can also be used as a learning tool since, thereby, one is able to understand better the system which is the object of study.

Abstract— The work presented in this article consists of the development of a decision-making support system, based on discrete event simulation models and aimed at a very specific class of production lines with a four closed-loop network configuration, allowing the company ownership to acquaint itself better with its current industrial reality and thus help in decision-making to maximize line performance.

Enrique Ares Gómez1 Gustavo Peláez Lourido2 Marina Salgado3 José Diéguez Quintas4

Luís Pinto Ferreira

The work described in this article consists of the development of a simulation model in an Arena environment, based on a real case, and is aimed at a very specific class of production lines, with a four closed-loop network configuration, commonly used in the automotive sector. This study is a sequence of another, developed by Resano et al. [10,11,12,13], who designed one of the first analytical models for an assembly line in the vehicle sector as a network of four closed loops of machines, decoupled by intermediate buffers formed by conveyors. They consider that machines process pallets which are not univocally related to each other. Both in the analytical model, as well as in the simulation presented here, one can analyse the blocking and starvation phenomena on a complex production line; these models also consider the proportion of four- and two-door cars between the doors’ disassembly and assembly stations. There is no knowledge of any other work in specialized literature, in the area of simulation, considering all these factors which are of such specific relevance in the performance of these types of manufacturing systems [14,15]. There are, in fact, very few studies undertaken which use simulation as a support tool in the decision-making process in the context of networks of closed-loops production lines. There is, however, a wider range of bibliography whenever the purpose of the study presupposes the development of analytical models for these types of configurations.

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Luís Pinto Ferreira et al. / (IJAEST) INTERNATIONAL JOURNAL OF ADVANCED ENGINEERING SCIENCES AND TECHNOLOGIES Vol No. 2, Issue No. 2, 119 - 123

Kouikoglou [16] analyses assembly and disassembly production networks based on the first continuous flow simulator applied by Angelo et al. [17] in which the traffic of discrete parts is approximated by a continuous flow. However, this model does not consider the phenomena of blocking and starvation transmission in networks formed by several closedloops. Zhang [18] developed a graph model and an induction method to analyse the blocking and starvation phenomena in complex assembly/disassembly closed-loop networks of machines and intermediate buffers. However, in order to build the model, the author did not consider an external variable (x), which defines the relationship between pallets, which are not always univocally related to each other, in our case study the four-door cars proportion.

B3,7

B1,2

B2,3

B6,4

B7,3

B3,4

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B2,5

B4,2

B4,1

Figure 1 – Main automobile assembly line and preassembly lines

n12 n 23n 34 n 41 237 n 25 n 56 n 64 n 42  450

(1)

n 37 n 73 138

(3)

(2)

The fourth closed-loop defines the relationship between the number of pallets with doors in different preassembly states and the number of pallets of cars with disassembled doors via an external variable (x), according to Equation (4). This variable represents the four-door car ratio between the doors’ disassembly stations, located at M 2 , and the doors’ assembly stations, located at take on values of between 0 and 1.

ISSN: 2230-7818

Replacing the sum of their values in Eq. (4) the following is obtained [10]: (5)

The simulation model presented in this article is based on these equations in order to determine the number of pallets which must circulate on each of the 4 closed-loops which exist on the analyzed automobile assembly line. III.

CHARACTERISTICS OF THE DEVELOPED SUPPORT SYSTEM FOR DECISION-MAKING

In the context of this project, all the work was developed in an Arena simulation environment [8], whose simulation language constitutes a visual and flexible programming tool, directed at the object, since it simultaneously combines the construction of simulation models with the integration of different languages of general use: Visual Basic, C, C++. This language is based on the SIMAN simulation language [19].

Figure 1 represents the main automobile line as well as the doors and front axle preassembly lines as a network of four closed-loop machines and intermediate buffers formed by conveyors. The sum of the car bodies, doors and front axle assembly pallets stored in each of the intermediate buffers of the three first closed-loops remain, respectively, constant at any time and are defined by Equations (1) to (3). This fact, as well as other analyses undertaken to evaluate the influence of different variables which interfere in the performance of the automobile assembly line being studied, was previously analysed in [10, 11, 12, 13]. B5,6

n 5 and n 6 are the numbers of stations M 5 and M 6 , n 2 is the number of stations at M 2 , from the door disassembly stations, n 3 is the number of stations at M 3 , and n 4 is the number of stations at M 4 to the door assembly stations. The values n 2 , n 3 , n 4 , n 5 and n 6 remain constant. Where

n 25 +n 56 +n 64 +60 = (216 +n 23+n 34 )·(1 + x)

MODEL OF THE ASSEMBLY LINE

n 25 +n 56 +n 64 +n 5 +n 6 = (n 2 +n 3 +n 4 +n 23+n 34 )·(1 + x)

II.

Equation (4):

M 4 . This variable can

The purpose of the use of an Arena simulation environment was that of enabling the production engineer to evaluate the performance of the automobile assembly line, through the variation of different parameters, thus contributing to an improved specification, characterization and definition of the most efficient control system. With this objective in mind, a support system for decisionmaking was developed; this enables the automatically generation of different simulation models, allowing the user in the initial stage of simulation to interact with the system to be developed, through the introduction of various parameters such as:      

The four-door cars ratio (x); The processing time for each machine; The production sequence in accordance to each type of car (two- or four-door); The speed and length of the intermediate buffers formed by conveyors; Simulation time; The number of pallets circulating on the first three closed-loops.

Figure 2 presents the graphic interface which allows the user to configure the above mentioned parameters.

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Luís Pinto Ferreira et al. / (IJAEST) INTERNATIONAL JOURNAL OF ADVANCED ENGINEERING SCIENCES AND TECHNOLOGIES Vol No. 2, Issue No. 2, 119 - 123

Number of Cars / Hour

X=0,7: Number of Cars / Hour vs Number of pallets (Loop 1) 60 50 40 30 20 10 0 100

120

140

160

180

200

220

240

260

280

Number of pallets (Loop 1)

Figure 3 – The number of pallets on Loop 1 based on the number of cars / hour (X=0,7)

COMPARATIVE ANALYSIS BETWEEN ANALYTICAL AND ARENA SIMULATION MODELS

X=0,7: Number of Cars / Hour vs Number of pallets (Loop 2) 60 50 40 30

It was demonstrated in [10, 13] that some governing equations of the four closed-loops are not compatible with the maximum capacities and the minimum contents of several intermediate buffers for certain values of the variable x. This incompatibility shows that an assembly line cannot operate in practice for x<0,37 in both, stationary and transitory regimes, and for x>0,97 in a stationary regime.

IV.

Figure 4 shows the impact that the variation in the number of pallets on loop 2 produces on the performance of the production line. Further analysis allows the conclusion that the line will block whenever the number of pallets is below 383 or above 543. On the other hand, one can see that, for a number of pallets above 398 and below 544, the number of cars produced per hour is always the same, the number being 55,5.

Number of Cars / Hour

Figure 2 – Parameterization of the automobile assembly line

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V. ASSESSMENT OF THE IMPACT OF THE NUMBER OF PALLETS, CIRCULATING ON THE FIRST THREE CLOSED LOOPS, ON THE NUMBER OF AUTOMOBILES PRODUCED PER HOUR

Using the simulation model developed in this research study, one sought to assess the influence that a variation in the number of the pallets on the first three closed loops has on the performance of the production line, translated into the number of cars manufactured / hour. In the real model, the number of pallets circulating on the first three closed loops is, respectively, 237, 450 and 138, and the value used for the proportion of four-door cars was that of 0,7. On observing figure 3, one may conclude that the number of pallets on loop 1 can vary between 119 and 262, with no resulting impact on the performance of the automobile production line. The number of cars produced per hour will remain constant, with an approximate value of 55,5 cars/hour. However, when the number of pallets on loop 1 is below 119 and above 262, this produces a blockage on the line.

20 10

0 350

400

450

500

550

600

Number of pallets (Loop 2)

Figure 4 – The number of pallets on Loop 2 based on the number of cars / hour (X=0,7)

Through the analysis of figure 5, and regarding the impact that the number of pallets’ variation produces on the performance of the production line, when circulating on loop 3 one can see that the line blocks when values are above 288. One can also conclude that, when the values range from 18 to 288, the number of automobiles produced is constant and equal, at 55,5 cars/hour. There is, however, a drop in production if the number of pallets is below 18, and production drops further as the number of pallets decreases in number. X=0,7: Number of Cars / Hour vs Number of pallets (Loop 3) 60

Number of Cars / Hour

Through the simulation model developed for the vehicle production line analysed, it was also verified that the system also did not function for values of x<0,37 and x>0,97, due to the blockage or starvation of some machines which constitute the model analysed [14]. It was similarly concluded that, once the minimum capacity of the buffers mentioned in [10,11] is reached, this ensures the continuous supply of machines with transport and assembly pallets.

50 40 30 20 10 0 0

100

150

200

250

300

350

Number of pallets (Loop 3)

Figure 5 – The number of pallets on Loop 3 based on the number of cars / hour (X=0,7)

The analysis undertaken previously, on the influence that the variation in the number of pallets circulating on the first

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Luís Pinto Ferreira et al. / (IJAEST) INTERNATIONAL JOURNAL OF ADVANCED ENGINEERING SCIENCES AND TECHNOLOGIES Vol No. 2, Issue No. 2, 119 - 123

TABLE 1 – THE NUMBER OF PALLETS ON LOOPS 1, 2 AND 3, BASED ON THE NUMBER OF CARS / HOUR (X=0,7)

Number of Pallets Loop 1

237

Loop 2

450

Loop 3

138

Loop 1

119

Proposal

Loop 2

450

for Alteration 1

Loop 3

138

Real Model

237

Loop 2

399

for Alteration 2

Loop 3

138

Loop 1

237

Proposal

Loop 2

450

for Alteration 3

Loop 3

55,5

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Loop 1 Proposal

Number of Cars / Hour

VI.

Conclusion

In this paper, an automobile assembly line and different preassembly lines were modelled as a network of four closed-loop machines and intermediate buffers formed by conveyors, constituting a configuration which is widely used in these kinds of assembly lines. Through an Arena simulation environment, a representative model of this line was developed with the purpose of providing the production engineer with a better understanding and assessment of its performance. The most relevant conclusion of the work presented in this article resides in the fact that it is possible to reduce the number of pallets circulating on the first three closed loops without affecting the performance of the production line. This fact has proved to be extremely useful since it allows a reduction in the costs ensuing from fewer pallets in circulation.

ISSN: 2230-7818

REFERENCES [1] Gonca Altuger, Constantin Chassapis ― Multi Criteria Preventive Maintenance Scheduling Through Arena Based Simulation Modeling‖, in Proceedings of 2009 Winter Simulation Conference, M. D. Rossetti, R. R. Hill, B. Johansson, A. Dunkin, and R. G. Ingalls, eds. [2] Pelaez, G. C.; Medina, V. & Ares, J. E. ― Manufacturing Control, Architecture of a Flexibel Cell Line‖, in Annals of DAAAM for 2000 & Proceedings of the 11th International DAAAM Symposium, ISBN 3901509-13-5, Published by DAAAM International, Vienna, Austria 2000, Editor B. Katalinic. [3] K. Feldmann, H. Rottbauer, N. Roth, ― Relevance of Assembly in Global Manufacturing‖ Keynote Papers: Presented at the Opening session, CIRP Annals – Manufacturing Technology, Volume 45, Issue 2, Pages 545-552, 1996. [4] Chrissoleon T. Papadopoulos, Michael E. J. O`Kelly, Michael J. Vidalis, Diomidis Spinellis, ― Analysis and Design of Discrete Part Production Lines‖, Springer Optimization and Its Applications, Volume 31, ISBN: 978-0-387-89493-5. [5] L. Jeff Hong, ― A Brief Introduction to Optimization via Simulation‖, in Proceedings of 2009 Winter Simulation Conference, M. D. Rossetti, R. R. Hill, B. Johansson, A. Dunkin, and R. G. Ingalls, eds. [6] Ricki G. Ingalls, ― Introduction to Simulation‖, in Proceedings of 2008 Winter Simulation Conference, S. J. Mason, R. R. Hill, L. Mönch, O. Rose, T. Jefferson, J. W. Fowler eds. [7] L. Valadares Tavares, Rui Carvalho Oliverira, Isabel Hall Themido, F. Nunes Correira, 1996, ― Investigação Operacional‖, Editora McGRAWHILL de Portugal, ISBN 972-8298-08-0. [8] W. David Kelton, Randall P. Sadowski, David T. Sturrock, 2007, ― Simulation With Arena‖, Fourth Edition, McGraw-hill Series, ISBN-13: 978-0-07-110685-6. [9] Luís Carlos Magalhães Pires, ― Análise de um Sistema de Programação da Produção (Scheduling) baseado em recursos Elementares (RE)‖, Dissertação de Mestrado em Produção Integrada por Computador, Departamento de Produção e Sistemas, Universidade do Minho. Fevereiro de 1999. [10] A. Resano Lázaro, 2007, ― Análisis Funcional y Optimización de la Distribuición en Planta de una Línea de Ensamblaje de Automóviles‖, PhD Thesis, directed by Prof. C. J Luis Pérez. Departamento de Ingeniería Mecánica, Energética y de Materiales‖, Universidad Pública de Navarra. [11] A. Resano Lázaro, C. J. Luis Pérez, 2007, ― Analysis of an automobile assembly line as a network of closed loops working in both, stationary and transitory regimes‖. International Journal of Production Research. Paper in Press. DOI: 10.1080/00207540601182294. [12] A. Resano Lázaro, C. J. Luis Pérez, 2007, ― Analysis and enhancement of the four-door cars proportion limits in a real automobile assembly line working in transitory regime‖, Second Manufacturing Engineering Society International Conference. Madrid. Spain. [13] A. Resano Lázaro, C. J. Luis Pérez, 2007, ― Dynamic analysis of an automobile assembly line considering starving and blocking. Robotics and Computer Integrated Manufacturing‖, Article in Press. DOI:10.1016/j.rcim.2007.11.002. [14] Luís Pinto Ferreira, E. Ares Gómez, G.C Peláez Lourido, A. Resano Lázaro, C. J. Luis Pérez, ― Comparative Analysis between analytical and Arena simulation models applied to an Automobile closed-loops assembly line, modelled like a network of closed-loops‖, in Proceedings of 25th International Manufacturing Conference: ― Manufacturing and Design – The Next Generation‖ (ICM2008), Ireland, 3rd-5th September 2008. [15] Ferreira, L[uís]; E. Ares, G[ómez]; G.C Peláez, L[ourido] & Salgado, M[arina] (2010). Analysis of the Influence of Conveyor Speed on the

X = 0,7

As perspectives of future work, some actuation lines stand out, as a natural continuation of the proposals presented here: • Impact evaluation that the sequence of production of different types of cars in the automobile assembly line performance. • Behaviour evaluation of the production line when a new car type is inserted.

three closed-loops produces on the performance of the automobile production line, allows the conclusion that it is possible to significantly reduce the number of pallets circulating on those loops, thus maintaining the production rhythm. Table 1 presents the limit values proposed for the number of pallets that can circulate in each of the three first closed loops without jeopardizing line performance. This conclusion has proved to be extremely important as it allows, potentially, a significant reduction in the costs ensuing from fewer circulating pallets. This fact, applied to a network configuration of four closed-loop machines and intermediate buffers formed by conveyors, has not been mentioned in specialized literature.

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Luís Pinto Ferreira et al. / (IJAEST) INTERNATIONAL JOURNAL OF ADVANCED ENGINEERING SCIENCES AND TECHNOLOGIES Vol No. 2, Issue No. 2, 119 - 123

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