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example Logio [Logio 2018]. and Dynamic Future [Dyn.Future DISCRETE EVENT 2018]. Very oftenthe Matlab (Simulink), Witness or Comsol [Humusoft 2018], [Dyn.Future 2017] or Plant Simulation (used SIMULATION USAGE TO in Skoda auto company -[Stocek, 2012]) softwareare used to visualize the necessary processes, usually using 3D graphics.For the basic analysis, however, programs designed for general MODEL AND OPTIMIZE THE process simulation, such as SIMPROCESS or SIMUL8 [Dlouhy 2011], can be used although 2D graphics oly is displayed to PRODUCTION LINE create a simulation model of the selected process and to MARTINA KUNCOVA, MICHAELA ZAJONCOVA analyze its possible extension, modification and alteration. Univeristy of Economics, Prague, Faculty of Informatics and The selection of the methodology for the simulation modelling Statisics, Dept. Of Econometrics, Prague, Czech Republic can be influenced by the analysis required by managers, DOI : 10.17973/MMSJ.2018_03_2017117 software package that is available or by the personal e-mail : [email protected] preferences of the modeler [Braisford 2014]. For the Simulation models are usually used in situations where complex production process analysis with a lot of random parameters it or complicated systems and processes need to be analyzed. The is usual to use discrete-event simulation (DES) as one of the main advantage of the simulation modelling is the fact that it is operations management techniques that is stochastic in nature. realized in virtual reality (in simulation software) without the All activities, their sequence, duration and required resources necessity to change the real processes. In this article the must be defined. In the following text we present the process of the model creation, verification and validation is manufacturing problem in company FOXCONN CZ dealing with described on the example of the Cisco routers production line the production of the Cisco routers. This article describes the in company Foxconn CZ. One part of the production line is simulation analysis of the production process of the routers. modelled in SIMUL8 software. The main aim is to verify options The main aim is the finding of the bottlenecks of the process for the line balancing improvement. For the activities’ duration and the analysis of the employees workload followed by the times the estimation of the probability distribution was made in suggestions for the production line improvement.The R software on the basis of real data or via the experts’ estimate. simulation model is developed in the environment of SIMUL8 After the process bottleneck findings according to the software. After debugging the model, results obtained from the simulation models’ results the changes in the production simulation runs are analyzed to find the main problems of the process were suggested. process and possibilities of improvements. The experiments are KEYWORDS performed with the objective to suggest the management the simulation model, production process, production line, routers, most responsible decision. SIMUL8 2 DISCRETE EVENT SIMULATION 1 INTRODUCTION Discrete event simulation (DES) is focused on modelling entities Simulation as a tool for the process analysis has started to be moving through a set of queues and activities. During the more important and widely used since the times of the process DES observes only the important events – it means only computers’ development in 1960s’ [Pidd 2014]. The main the time points where there is a change in the system (entity reason for using computer simulation in the analysis of arrival, start/end of an activity). Since these events occur at managerial problems is the impossibility of using any other, irregular intervals the simulation time in a DES model moves especially analytical tools due to complexity of real processes. forward in a jumps bridging the “no important” time between Over the years simulation modelling has become an effective the events – that is why it is called discrete-event [Dlouhy and robust part of the operations research and management 2011], [Robinson 2014]. science [Braisford 2014], [Rotaru 2014] although nowadays it might also be seen as an IT or statistical tool. Simulation means DES usually models queuing systems as they progress though a technique for imitation (by a computer model) of some real time describing entities (people, products, material etc.) situations, processes or activities that already exist in reality or moving through a network of queues and activities and using that are in preparation [Banks 1998). Models can be created in limited resources during activities [Robinson 2014]. In each various software packages depending on the type of the model simulation study a set of several phases should be followed or on the type of the analysis planned. Sometimes Monte Carlo [Wainer 2009], [Dlouhy 2011], [Rotaru 2014]: simulation for iterative evaluation of a deterministic model is - Problem formulation sufficient but real simulation is usually made via discrete event - Conceptual model simulation or continuous simulation model [Dlouhy 2011]. - Collection and analysis of input/output data Simulation could be applied to various kind of processes from - Modelling phase/computer simulation model manufacturing production lines [O’Kane 2000], [Masood 2006], - Verification and validation [Montevechi 2007], [Aguirre 2008], [Ficova 2013], [Fousek - Experimentation with the model 2017] and call centers or help desks [Kuncova 2007] to health - Results comparison and description care models and hospital processes [Günal 2010], [Ghanes - Implementation 2014], [Voracek 2014]. Similar phases could be used in system dynamics methodology but it is more static model based on differential equations and Simulation of production processes can be found in various it is generally deterministic which might be less suitable for the types of industries and at all stages of production - examples in production process modelling [Braisford 2014]. While in system the Czech Republic can be found on the pages of companies dynamics the processes are viewed as a series of stock and that create simulationmodels for other companies – for flows, DES describes the system by a network of queues and MM SCIENCE JOURNAL I 2018 I MARCH 2325 activities and the models are simulated in unequal time steps functionality. It allows user to create a visual model of the given by the time between an important events. Other analyzed system by drawing objects directly on the screen of a possibility is agent based simulation model where the system is computer [Concannon 2007], [Elder 2014]. Contrary to similar described from the point of view of individual objects (product, simulation software like Witness or Plant Simulation that are person) interacting with each other and with the environment. more suited for the production modelling via 3D animation, It is only a different point of view on the same problem. As it SIMUL8 uses 2D animation only to visualize the processes. Each was mentioned before the simulation model is influenced by model in SIMUL8 is usually developed via 6 main parts: Work the aim of the manager/decision-maker who needs the results Item, Work Entry Point, Storage Bin, Work Center, Work Exit from the model and by the software available. DES usually Pont, Resource [Concannon 2007]. seems to be an easier and more understandable way of modelling the production or business processes. Work Item represents a dynamic object(s), usually called entities (such as customers, products, documents or other Simulation model usually helps the companies to see how entities) that move through the activities and processes, might changes in the process could influence the inputs, other change their characteristics and use various resources. Their processes, queues etc. O’Kane et al. showed the importance of main properties that can be defined are labels (attributes), discrete-event simulation for the decisions to increase in total image of the item (showed during the animation of the production output [O’Kane 2000] - their simulation results gave simulation on the screen) and advanced properties (multiple important insights into the behaviour of the real system and Work Item Types). provided invaluable knowledge to the company as to the perceived benefits of change within the current production Work Entry Point is an object that generates entities (Work facilities. Masood via DES model investigated how to reduce Items) into the simulation model according to the selected the cycle times and increase in the machine utilization in an distribution of the inter-arrival times. Other properties that can automotive plant – in his study the cycle time cylinder block be used in this object are batching of the Work Items, changing line was reduced by 32 % and the throughput was increased by of the Work Items’ Label or setting of the following discipline 65 % [Masood 2006]. Montevechi et al. showed the meaning of called Routing Out. simulation experiments representing different scenarios and company strategies [Montevechi 2007]. Aguirre et al. Storage Bin is used for queues or buffers where the Work Items developed the simulation model focused on the production wait before next processes. It is possible to define the capacity process of car-parts and they recommended, among other of the queue or the shelf life as a time units for the expiration. things, to the company to use the simulation tool to try different scenarios to get more experience and knowledge Work Center represents the main