Simulation Model of Manufacturing using WITNESS Software

Simulation Model
Simulation Model

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Simulation Model of Manufacturing using WITNESS Software


Nowadays, simulation models which are designed based on varied simulation software have gained wide utilisation in the evaluation of different aspects of manufacturing systems. In this group project, the WITNESS software will be applied to simulate the packaging process of an automobile manufacturing assembly line in a production company that is cost-conscious and interested in introducing a new product (Ceric, 2014). Technically, line balancing through optimization of the manufacturing and packing processes is one of the components of improving production efficiency in manufacturing industries.

As a result, the concept of manufacturing process optimization itself is based on the fact that everyone as well as the machines is working together in a balance in a manner that the amount of work carried out by staff or machines with similar capacities is the same, and the variation is smoothed to ensure that no particular element of the production process overburden (Carrie, 2014). This is aimed at ensuring that waiting time for work is alleviated and therefore it is carried out in a well organized and single piece flow.

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The Description of the System that is going to be Modelled and the Problem(s)

Inadequate software experimentation irrespective of adequate modelling is usually among the leading causes of poor decisions in manufacturing companies and often gives detrimental results, especially when there is involvement of financial investment (Ballakur & Steudel, 2007). The group project is about a weighing and packaging process simulation model in a manufacturing company based on WITNESS software. The group project is regarding improvement of the performance of the packing area with the help of simulation model.

The automobile company produces both motor vehicles and respective motor body parts by implementing lean manufacturing system in their plant. The main objective of this simulation model based on WITNESS software is to strive to reduce congestion at the packaging area of an automobile manufacturing company’s assembly line, particularly by improving the efficiency and productivity of weighing and inspection as well as wrapping and cartoning processes through precise simulation.

For this project, our group modelled the functions or operations of the packaging area of Nissan Motor Manufacturing (UK) Limited, which was selected due to the challenges they were experiencing when the company was undertaking an aggressive expansion strategy not only in its Sunderland manufacturing plant, but also in other regions in the United Kingdom and across the world.

However, due to the limitations of the WITNESS simulation software as well as the short duration through which the project had to be completed, our group opted to settle for a section of the manufacturing process, that is, the packaging where various processes are carried out.

As a result, our group decided to focus on only some aspects of the packaging section, particularly the last stage of quality control which is the final inspection and weighing of various body parts as well as wrapping and packaging of the motor body parts in cartons. In particular, we modelled the packaging of bush press for its latest model of car known as Qashqai.

The reason why we chose this problem for the simulation model is attributable to the fact that, Nissan company was a good case of how many automobile manufacturing companies are faced my numerous challenges when it comes to addressing the challenge of space utilization and reduction of congestion not only in their packaging section, but in the entire manufacturing process as a whole even though the former is more imperative considering that, it is the last stage in the manufacturing process prior to the body parts being taken to the warehouse awaiting to be shipped overseas or transported for distribution (Lanner, 2013).    

This choice was further attributed by the fact that, some data was available online in addition to the potential of making estimations that are not significantly different from the anticipated results of the actual manufacturing process. Thus, considerable data was collected concerning Nissan Motor Manufacturing Company Limited, particularly the manufacturing plant which is based in Sunderland.

This was further enhanced by making estimates that were not significantly different from the actual production process data. No particular visit was made to the actual manufacturing plant location, but quite a lot of time was spent discussing the various aspects of the manufacturing process data including the processes included in the packaging section, arrival profile of the finished body parts, shifts of employees working in the packaging section as well as the durations needed to each of the considered process for each body part.

Sometimes the packaging area may involve many activities, but in our project we specifically focused on the final inspection and weighing of the finished body parts particularly the bush press as well as the wrapping and cartoning of the bush press prior to being taken to the warehouse for storage awaiting dispatch to the market. We focused on bush press because of their peculiar nature which makes their demand extremely high in the market, especially at a time like this when Nissan Motor Manufacturing Limited was experiencing tremendous growth in its production capacity due to increased market demand.

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In an automobile manufacturing market which is hugely competitive, Nissan has to no option but making sure that it demonstrates superb value for money in its attempts towards securing contracts for new car models’ production (Lanner, 2013). This is attributable to the fact that these new contracts for the manufacturing of new car models can only be secured by companies that have the ability to provide the best option in manufacturing with regards to cost, delivery, and quality.

In particular, the Nissan manufacturing plant in our group project faces stiff competition not only from competitors in the market but also other Nissan plants located in UK as well as across the world. As a result, the Nissan manufacturing plant based in Sunderland is without any doubt in desperate need to make sure that there is optimization of its production processes, especially for the manufacturing of the latest Nissan’s Qashqai car model (Lanner, 2013).

This was to a significant extent motivated by the introduction of the suspension plant that was specifically installed for the manufacturing of the Qashqai model, and the company needed to succinctly understand and outline the role of this newly introduced automobile manufacturing technology (Lanner, 2013).

In addition, there was need to delve into details of the sources of congestion in the packaging section which was becoming a common phenomenon sometimes hindering smooth production flow due to lack of space for convenient and flexible manoeuvring of company employees during manufacturing processes as well as limiting storage space of finished bush press automobile body parts and delays in market delivery to meet the orders placed for finished parts.

There are also other aspects of the simulation scenario that have the potential to impact the throughput of the automobile company including number of employees, production durations, number of automobile parts that can be at a time, sources of raw materials, the market demand, technology employed in the manufacturing assembly line and packaging, size of the warehouse and many others (Fishwick, 2008).

Most of these aspects can not be easily altered without expensive changes have to be made to the company, which is mainly the reason why in this group project we are going to begin by optimizing the packaging section efficiency and performance, particularly the inspection and/or weighing as well as wrapping and cartoning processes. The WITNESS software simulation group project will be divided into five main parts.

These parts are particularly: the introduction, the role/importance of WITNESS simulation software in company manufacturing process, model build process and analysis of collected data, implementation of the simulation model as well as the improvement of the simulation model and conclusion.

The introduction part will provide basic and/or background information about simulation models in company manufacturing process and in particular emphasizing on WITNESS simulation software on which this project will be based. The purposes for which software based simulation models have been used in manufacturing will be discussed in this part.

In addition, the place of simulation in contemporary manufacturing processes will also be discussed together with the progressive use and progress made in computer simulation models to simulate various manufacturing systems and/or processes for reduction of costs and improved productivity. The essence of the wide usage of simulation in company manufacturing processes as a stylish, flexible and contemporary management tool will be highlighted.

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The second part will discuss the role of simulation in manufacturing process. An emphasis will be put on reviewing literature to provide evidence on the use of simulation in manufacturing process. In this part, focus will be on production aspect of the manufacturing process and how simulation modelling has been used to facilitate making of decisions and its imperativeness in solving production management problems.

The third part will present the simulation model building process with an emphasis on elucidating how the simulation model will be executed. This will be done simultaneously with collection of data and analysis of the results of the simulation model in order to identify the bottlenecks of the manufacturing process or production system as well as the underlying issues that cause the problems.

The fourth part will be concerned with the implementation of the developed simulation model based on WITNESS software in order to identify, verify and validate the simulation model results. Finally, the last part will discuss the modifications if necessary that will be made on the developed simulation model in order to improve the manufacturing process for increased total output (productivity) and maximization of inventory of products. Lastly, recommendations and a conclusion on the simulation project and the developed simulation model based on WITNESS software will be provided.  

The Conceptual Model

The packaging section consists of six weighing and inspection machines {m = 1, 2, 3, 4, 5, 6} and each of the machines work at the same rate and similar in specifications as well as stop time intervals, even though the frequency of stoppages are randomly distributed between all the six machines. The stoppage interval of the six weighing and inspection machines is approximately a negative exponential distribution of 240 minutes and upon stoppage the repair time range between a minimum of 15 minutes and a maximum of 20 minutes.

Fifty applications (bush press automobile parts) arrive in every 30 minutes and are buffered into a queue awaiting to be inspected and weighed by the inspection and weighing machines prior to wrapping and eventually being put into cartons. This operation takes duration of between 2 and 10 minutes for each application (bush press automobile parts) meaning the process a uniform cycle time of between 2 and 10 minutes.

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From the inspection and weighing machines the applications (bush press automobile parts) are directed into another queue of the packaging or wrapping machines where they are wrapped before being put into cartons and then taken to the warehouse for storage awaiting dispatch to the market. There are two packaging or wrapping machines arranged in a conveyor format each with a capacity of 1000 applications (bush press automobile parts) meaning the total buffering capacity of the wrapping machines is 2000.

Subsequently, the wrapped applications (bush press automobile parts) are directed to the cartoning machines which package them into cartons. There are four cartoning machines {m = 1, 2, 3, 4} which operate effectively throughout unless during planned maintenance shutdown and during this period the production is temporarily stopped or a contingency plan is implemented in case there is a high demand. This operation takes duration of between 2 and 15 minutes for each application (bush press automobile parts) meaning the process a uniform cycle time of between 2 and 15 minutes. The packaging area operations are illustrated in the conceptual model shown below:

Figure 1: Conceptual Model

A combination of the conceptual model simulation modelling information with the shifts, sub-shifts as well as shifts and sub-shifts breaks the outcome of running the simulation model based on the specifies rules both the model outcome without element flow illustrations and the one with element flow illustrations are shown in Figure 2 and Figure 3 shown below respectively:  

Figure 2: Final Model without Elements Flow

Figure 3: Final Model with Elements Flow

The Data Collection and Input Modelling Process

Data collection

According to Ballakur & Steudel (2007) data collection constitutes the most imperative part of the entire despite of it being a very daunting, frustrating as well as time consuming task mainly because it sets the stage for the simulation project as a whole. As a result, the time needed to develop the simulation model may significantly vary based on the extent of quality and quantifiable data that should be collected prior to beginning the actual simulation.

Banks and Carson (2004) argued that even when the validity of a simulation model structure has been confirmed, if collected data is inputted incorrectly collected, followed by inappropriate analysis, the resulting simulation output will not be a representation of the actual environment, and will provide misleading and possibly damaging information. In this group project, the data was not fully available and the collected data was supplemented by some tentative estimation to ensure significant variation was not witnessed between the actual production scenario and the simulation scenario.

In particular, the data was collected about Nissan’s packaging section processes specifically on the arrival profile, shifts and sub-shifts, activity cycle times, capacity of queues,  as well as stoppages of the inspection and weighing machines for the bush press body parts from the assembling line.

Arrival Profile


Day shifts

Period TypeWorking PeriodRest TimeOvertimeSubshift NameTotal
1Subshift4809600Day subshift1440
2Subshift4809600Day subshift1440
3Subshift4809600Day subshift1440
4Subshift4809600Day subshift1440
5Subshift4809600Day subshift1440
6Subshift24012000Day subshift1440
7Subshift24012000Day subshift1440

Breaks during Shifts

Period TypeWorking TimeRest TimeOvertimeSubshift NameTotal

Stoppages of the Final Inspection and Weighing Machines    

Final Inspection and Weighing Machine Operation Stoppages
Busy TimeNegative exponential distribution of 240 minutes 
Repair TimeA uniform distribution of 15 minutes minimum and 20 minutes maximum

Simulation rules were also considered whereby all input rules were set to be push and the output rules were set as pull i.e. the default rules in the simulation model settings. As a result, the simulation rules were used to connect the flow of elements through the simulation model from start to finish.

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