Modeling and simulation for optimization of a mattress production line based on flexsim software at dunlopillo (vietnam) LTD

stay time and input/output quantity of all objects in the Cover Section – Actual simulation model...45 Table 3.. stay time and input/output quantity of all objects in the Spring Section

MINISTRY OF EDUCATION AND TRAINING HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY AND EDUCATION FACULTY FOR

HIGH QUALITY TRAINING

INDUSTRIAL MANAGEMENT

MODELING AND SIMULATION FOR OPTIMIZATION OF A MATTRESS PRODUCTION LINE BASED ON FLEXSIM SOFTWARE AT DUNLOPILLO

(VIETNAM) LTD

SUPERVISOR: MBA NGUYEN DANH HA THAI STUDENT: DO THUY LINH

SKL008186

MINISTRY OF EDUCATION AND TRAINING HO CHI MINH CITY

UNIVERSITY OF TECHNOLOGY AND EDUCATION FACULTY FOR

HIGH QUALITY TRAINING

GRADUATION THESIS

Topic:

MODELING AND SIMULATION FOR

OPTIMIZATION OF A MATTRESS PRODUCTION

LINE BASED ON FLEXSIM SOFTWARE AT

INSTRUCTOR’S COMMENTS

-

-Ho Chi Minh City, day … month … year

…

Instructor

MEMBER OF THE THESIS

COMMITTEE’S COMMENTS

-

-Ho Chi Minh City, day … month … year

…

Member of the Thesis committee

ii

The process of completing the graduation thesis is the most important stage in every student's life It is the hardest time for me because I did present the biggest challenge that I’ve never met with full of efforts Graduation thesis gives me an opportunity to review all knowledge and skills in four years of university before starting a career First of all, I would like to express my sincerity, thanks to teachers of the Faculty for High Quality Training and the Faculty of Economy who always have enthusiastically taught and equipped students with all necessary knowledge and experience.

Secondly, I would like to express my gratitude to my instructor Mr Nguyen Danh Ha who gave me all useful guidance and enthusiastic support Th ey are very valuable suggestions not only in the process of making this thesis but also as a stepping stone for me in the process of studying and setting up a career in the future.

Finally, thank you to my family and my friends who are always by my side and encourage me to overcome all my hard times.

Because of the time limit, the difficulty in approaching such a new researching direction i.e Simulation and lack of experience, the thesis cannot avoid mistakes and shortages Therefore, I am extremely appreciated to receive comments and recommendation from you to help me to complete this graduation thesis as well as possible.

Thank you so much,

LIST OF ACRONYMS

LIST OF TABLES

Table 2 1 The advantages and disadvantages of four basic layout types 13

Table 2 2 Characteristics of a manufacturing system model 19

Table 2 3 The advantages & disadvantages of Simulation 21

Table 3 1 The working schedule 24

Table 3 2 The average daily yield of mattress production system in third quarter, 2020 25 Table 3 3 The Average Production Productivity Rate per day 26

Table 3.4 The demand forecast for 2023 27

Table 3 5 List of machines and processing tables in the mattress production line 28

Table 3 6 Table of processing time of machines and processing tables in the mattress production line 29

Table 3 7 The output of mattress production line - the actual model 42

Table 3 8 Detail state of all objects in the Cover Section – Actual simulation model 44 Table 3 9 Detail Avg stay time and input/output quantity of all objects in the Cover Section – Actual simulation model 45

Table 3 10 Detail state of all objects in the Spring Section – Actual simulation model 47 Table 3 11 Detail Avg stay time and input/output quantity of all objects in the Spring Section – Actual simulation model 49

Table 3 12 Detail state of all objects in the Finishing Section – Actual simulation model 50

Table 3 13 Detail Avg stay time and input/output quantity of all objects in the Finishing Section – Actual simulation model 51

Table 4 1 The output of mattress production line - Scenario1 simulation model 54

Table 4 2 Detail state of all objects in the Cover Section – Scenario1 simulation model 56 Table 4 3 Detail Avg stay time and input/output quantity of all objects in the Cover Section – Scenario1 simulation model 57

Table 4 4 Detail state of all objects in the Spring Section – Sncenario1 simulation model 59 Table 4 5 Detail Avg stay time and input/output quantity of all objects in the Spring

Table 4 6 Detail state of all objects in the Finishing Section – Scenario1 simulationmodel 61Table 4 7 Detail Avg stay time and input/output quantity of all objects in the

Finishing Section – Scenario1 simulation model 62Table 4 8 The output of mattress production line - Scenario2 simulation model 64Table 4 9 Detail state of all objects in the Cover Section – Scenario2 simulation model66

Table 4 10 Detail Avg stay time and input/output quantity of all objects in the CoverSection – Scenario2 simulation model 67Table 4 11 Detail Avg stay time and input/output quantity of all objects in the SpringSection – Scenario2 simulation model 68Table 4 12 Detail state of all objects in the Finishing Section – Scenario2 simulationmodel 70Table 4 13 Detail Avg stay time and input/output quantity of all objects in the

Finishing Section – Scenario2 simulation model 71

LIST OF FIGURES

Figure 0 1 Process of the research deployment 3

Figure 1 1 Image of Dunlopillo Vietnam Ltd 5

Figure 1 2 Medium End (ME): DUN AUDREY N) MATT 200X180X25CM VN 6

Figure 1 3 High End (HE): DUN FIRMREST LUXE MATT 205X193X25CM BS 6

Figure 1 4 Very High End (V-HE): DUN CORINA PRE MATT 200X160X35CM (N) 7 Figure 1 5 DUN LATEX WORLD PURE MATT 200X160X20CM 7

Figure 1 6 Factory Organization Chart 8

Figure 2 1 Volume and variety characteristics for each process type 10

Figure 2 2 The volume – variety characteristics influence the manufacturing layout 12 Figure 2 3 The relationship between manufacturing process types and basic layout types 14

Figure 2 4 A logo image of Flexsim software 20

Figure 3 1 Mattress production process 24

Figure 3 2 2D Layout drawing of Spring Section 30

Figure 3 3 2D Layout drawing of Cover Section 31

Figure 3 4 2D Layout drawing of Finishing Section 31

Figure 3 5 3D Logic model of Glue – box station 33

Figure 3 6 Setup of the Glue-box table 4’s properties for 3D Logic model 33

Figure 3 7 Setup of the PU Sheet queue’s properties for 3D Logic model 34

Figure 3 8 Process flow for activities at Glue-box station 35

Figure 3 9 Setup parameters for Process Flow Properties 35

Figure 3 10 3D model of process flow for Glue – box station 36

Figure 3 11 Setup parameters for Source Quilting Top 37

Figure 3 12 Setup parameters for Quilting Top machine 38

Figure 3 13 The complete existing 3D model of mattress production line 38

Figure 3 14 All of process flows for the logic model 40

Figure 3 15 State of all objects in the Cover Section Pie chart – Actual simulation

model 44

Figure 3 16 Average stay time of Semi – Mattress on Queue in the Cover Section Bar chart – Actual simulation model 46

Figure 3 17 State of all objects in the Spring Section Pie chart – Actual simulation model 47

Figure 3 18 Average stay time of Semi – Mattress on Queue in the Spring Section Bar chart – Actual simulation model 48

Figure 3 19 State of all objects in the Finishing Section Pie chart – Actual simulation model 50

Figure 3 20 Average stay time of Semi – Mattress on Queue in the Finishing Section Bar chart – Actual simulation model 51

Figure 4 1 The 3D model design of the Scenario1 54

Figure 4 2 Pie chart of Cover Section – Scenario1 simulation model 55

Figure 4 3 Bar chart of Cover Section – Scenario1 simulation model 56

Figure 4 4 Pie chart of Spring Section– Scenario1 simulation model 58

Figure 4 5 Bar chart of Spring Section– Scenario1 simulation model 59

Figure 4 6 Pie chart of Finishing Section– Scenario1 simulation model 61

Figure 4 7 Bar chart of Finishing Section– Scenario1 simulation model 62

Figure 4 8 The 3D model design of the Scenario2 64

Figure 4 9 Pie chart of Cover Section– Scenario2 simulation model 65

Figure 4 10 Bar chart of Cover Section – Scenario2 simulation model 66

Figure 4 11 Bar chart of Spring Section – Scenario2 simulation model 68

Figure 4 12 Pie chart of Finishing Section– Scenario2 simulation model 69

TABLE OF CONTENTS

INSTRUCTOR’S COMMENTS i

MEMBER OF THE THESIS COMMITTEE’S COMMENTS ii

ACKNOWLEDGEMENT iii

LIST OF ACRONYMS iv

LIST OF TABLES v

LIST OF FIGURES vii

INTRODUCTION 1

1 Reasons for choosing the topic 1

2 Objectives of the study 2

3 Scope and object of the study 2

3.1 Object of the study 2

3.2 Scope of the study 2

4 Methodology of the study 2

5 Structure of the thesis 3

CHAPTER 1: INTRODUCTION OF DUNLOPILLO VIETNAM LTD 5

1.1 History and development of the company 5

1.2 Main products 6

1.3 Manufacturing organization chart 8

CHAPTER 2: LITERATURE REVIEW 9

2.1 Manufacturing process types, basic layout types and the relationship between them 2.1.1 Types of manufacturing processes 9

2.1.2 The basic layout types 11

2.1.3 The relationship between manufacturing process types and basic layout types 13

2.2 Bottleneck 14

2.2.1 Definition 14

2.2.2 Types of bottleneck 14

2.2.3 Bottleneck detection methods 15

2.2.4 Type of data for bottleneck analysis 16

2.3 Modeling and Simulation 17

2.3.1 Modeling and Simulation definition 17

2.3.2 The purpose of Modeling and Simulation 18

2.3.3 Modeling of manufacturing system 18

2.3.4 Simulation tool 19

2.3.4.1 Introduction of Flexsim software 20

2.3.4.2 Advantages and disadvantages of Simulation 21

CHAPTER 3: CURRENT PROBLEMS AND THE IMPLEMENTATION OF MODELING & SIMULATION OF THE ACTUAL MATTRESS PRODUCTION LINE 22

3.1 Mattress production process description 22

3.2 Current problem description 25

3.2.1 Current production perspective 25

3.2.3 Future demand forecast 26

3.3 Data collection and analysis 27

3.4 Modeling the simulation with Flexsim software 29

3.4.1 Some assumptions of simulation model 29

3.4.2 Steps of modeling 30

3.5 Simulation results and analysis 40

3.5.1 Simulation running 40

3.5.2 Results and analysis 41

3.5.2.1 Type of output data for analysis 42

3.5.2.2 Output data analysis 43

CHAPTER 4: PROPOSAL OF NEW DESIGNS FOR CAPACITY AND EFFICIENCY IMPROVEMENT OF THE MATTRESS PRODUCTION LINE 53

4.1 Scenario1 for efficiency improvement of the current mattress production line 53 4.1.1 Design of the Scenario1 53

4.1.2 Result and analysis of the effectiveness of the Scenario1 54

4.2 Scenario2 for capacity improvement of the mattress production line 63

4.2.1 Design of the Scenario2 63

4.2.2 Result and analysis of the effectiveness of the Scenario2 64

CONCLUSION 72

REFERENCES 74

1 Reasons for choosing the topic

According to an article by the Industry and Trade newspaper published on October 22,

2019, a study on the mattress market by Mekong Capital indicated that the Vietnamesemattress market has a size of about 1 billion USD with an estimated need of 4 millionnew mattresses However, there are still 60% of families that have not used them, sothere are still a lot of chances for growth The business world predicts that in thefuture, the mattress market will expand, because the mattress will be an essential item

in every Vietnamese family

Currently, Dunlopillo Vietnam focuses on production for export, so it has not reallypayed attention on the domestic market However, realizing the potential of theVietnamese market, in the next two years when the covid19 pandemic will becontrolled, the company is going to planning for developing and expanding marketshare in Vietnam

Additionally, in Indonesia, Dunlopillo is one of two mattress brands which have beenbeing dominant in the mattress market Population growth and migration of consumersfrom rural to urban areas are creating more mattress demand both residential and non –residential segment (e.g hotel, resort, …) Therefore, based on the forecast of Salesdepartment, the company also needs to deal with this increase

According the company’s expansion plan, to cope with this problem, Modeling and Simulation has been a profitable method to analyze, assess the current status of the

system and modify for improvement It is able to precisely anticipate the performance

of complicated systems, makes it ideally suitable for system planning (Harrell etal.2012) Application of simulation prevents the company from blindly expanding thescale of production to improve capacity

In this study, Flexsim 2019 which is one kind of simulation software was applied, is astate-of-the-art tool for user to simulate and optimize the production line

2 Objectives of the study

This study aims to:



machines, stations are working inefficiently

Determine and eliminate the bottleneck in the production line, analyze reasons caused it



Whether the current fixed-resources are enough to meet the demand, or not.Which expanding resources plan is suitable and meet the objectives set

3 Scope and object of the study

3.1 Object of the study

The object of this thesis is the mattress production line at Dunlopillo Vietnam Ltd

3.2 Scope of the study

Scope of mattress type: the company has hundreds of types of mattresses classified by

model and size, so it is extremely difficult to simulate in the software Therefore, threemain mattress models represent three product segments, structure and size according toforecast demand chosen:

+ Contract (2mx1m8) – Bonnel Spring

+ Duchess (2mx1m8) – IPS Spring

+ Marilyn (2mx1m8) – CPS Spring

Scope of time: in the next 2 years.

Scope of area: the plant of Dunlopillo Vietnam Ltd.

Scope of data: collected in 2020.

4 Methodology of the study

It combines several methods: Observational and documentary methods to collect data for analysis of the actual production line The existing model is analyzed and imported

into Flexsim 2019 software After running this simulation model, problems in theproduction line will be figured out by analyzing output data Next, new models will bedesigned to solve the problems until satisfy the targets and objectives In this study,decision-making bases on simulation result This simulation method plays animportant role in providing information to determine every solution To make themethodology more clarify, it is summarized in this Figure below.

Figure 0 1 Process of the study deployment

Source: Author’s compilation

5 Structure of the thesis

In the process of learning this thesis, to make it easier to follow and understand, Iwould like to briefly present all main content below:

Chapter 1: Introduction of Dunlopillo Vietnam Ltd.

This chapter introduces information about Dunlopillo Vietnam Ltd such as the process

of formation, development, field of activity, products

Chương 2: Literature review

All theories laying foundation for the study are shown in this part

Chapter 3: Current problems and the implementation of modeling & simulation

of the mattress production line

This chapter presents about the production process overview, current perspective, allsteps from designing to simulating the actual model in flexsim software and analyzingthe results of the simulation

Chương 4: Proposal of new designs for capacity and efficiency improvement of the actual mattress production line

After finding out problems, in turn, improvement Scenarios are designed, simulatedand analyzed to find the solutions for all the problems

CHAPTER 1: INTRODUCTION OF DUNLOPILLO

VIETNAM LTD.

1.1 History and development of the company









An Town, Binh Duong Province, Vietnam

establishment (1929) in the UK and more than 24 years of establishing a factory inVietnam (1997), along with great experience and potential, Dunlopillo become afamiliar, reliable mattress brand for families, hotels, resort chains in both Vietnamesemarket and in the world Products of Dunlopillo Vietnam are mainly exported toforeign markets (Asia – Pacific), such as Singapore, Malaysia, China and other smallmarkets like Korea, Cambodia, Brunei, Myanmar, Hong Kong, Saudi Arabia, etc.

1.2 Main products

At the factory in Vietnam, the company mainly produces spring mattresses, andassembles latex mattress All Dunlopillo products range from medium to very high-end segments to meet the needs of all domestic and foreign customers, from personalconsumption to hotel service business Here are some illustrations for each mattressline and segment:

Figure 1 4 Very High End (V-HE): DUN CORINA PRE MATT 200X160X35CM (N)

Source: Dublopillo.com.vn



Figure 1 5 DUN LATEX WORLD PURE MATT 200X160X20CM

Source: Dublopillo.com.vn

1.3 Manufacturing organization chart

Figure 1 6 Factory Organization Chart

Source: Document from HR Department

CHAPTER 2: LITERATURE REVIEW

In this study, simulation by Flexsim software is applied for analyzing the manufacturingprocess Therefore, this chapter 2 will in turn point out the related theoretical bases

The first one is the theory of factory layout design Simulation will build the entireproduction process, layout of machines and workers Therefore, determining the layoutdesign plays an extremely important role In addition, to understand the layout design,

it is necessary to know what factors are related to and affect the layout of the factorysuch as manufacturing process, production method

Next, this study will focus on analysis to identify bottlenecks that reduce productionefficiency, so this chapter will learn about what is the bottleneck? How does it effect

on production efficiency? what are methods and measure factors used to find out theseproblems

And finally, the chapter 2 will introduce the Modeling & Simulation method, theFlexsim simulation software, the use and effectiveness of this method for the study aswell

2.1 Manufacturing process types, basic layout types and the relationship between them

2.1.1 Types of manufacturing processes

According to Slack et al (2010), there are five types of manufacturing processes whichinclude Project processes, Jobbing processes, Batch processes, Mass processes andContinuous processes Different operations, even those in the same operation, may adoptdifferent types It depends on attributes of the operation such as the variety and volume of

the product which need to be produced The Figure 2.1 shows the relationship between the

types of manufacturing processes and 2 dimensions of volume and variety

Figure 2 1 Volume and variety characteristics for each process type

Source: Operations management book.

All the content about the manufacturing process types is displayed below following to the Operations management book of Slack et al (2010):



Project processes usually handle highly customized products The time needed tocomplete the product or service is pretty long Therefore, low volume and high varietyare characteristics of this project processes Because of high customization, theactivities in production can be ill-defined and uncertain They often change to meet thecustomer demand



Jobbing processes also deal with high variety and low volumes, just behind projectprocesses In jobbing processes, products have to use the same resources with the differentmodification for each product requirements It different from project process where eachproduct has its own resources This type of process produce more and usually smalleritems than project process and they also have common in low repetition



Batch processes can be quite similar to jobbing processes, but it cannot produce variously

as jobbing processes Each time batch processes more than one product, so size of thebatch could be just two, three or more, in which case the batch process would

differ little from jobbing Conversely, if the batches are large, and especially if theproducts are familiar to the operation, batch processes can be fairly repetitive Because

of this, the batch type of process can be found over a wide range of volume and varietylevels



Mass processes deal with production in high volume and pretty narrow variety It issuitable for the production of the large number of products which are the same orsimilar, the different variants of its product do not affect the basic process ofproduction Several variants of a product could be produced on a mass process such as

an assembly line, but the process itself is unaffected The equipment used at each stage

of the process can be designed to handle several different types of components loadedinto the assembly equipment



Continuous processes operate at highest volume and lowest variety with longer periods

of time compared to mass processes In this processes, products are in an endless flow.Continuous processes are often associated with relatively inflexible, capital-intensivetechnologies with highly predictable flow

2.1.2 The basic layout types

Also according to Slack et al (2010), There are four basic layout types: Fixed-positionlayout, Functional layout, Cell layout and Product layout All practical layout didderive from them The types of layouts are also the same to types of processes, theyhave to be suitable to characteristics of the products: the company has low or highvariety of products, and low or high volume So that The layout types are also relevant

to these two dimensions

Figure 2 2 The volume – variety characteristics influence the manufacturing

layout Source: Operations management book

Base on the Operations management book of Slack et al (2010), the content and

concept of the layout types are presented below:



Fixed-position layout let the product stationary at fixed place while people, equipment,machinery, material move to it as necessary This layout uses for product which isimpossible to move conveniently such as: products are too large (Ship, airplane, …),too delicate e.g surgery, or it could object to be move e.g high class service in hotel

or restaurant, everything is on-site service, so customer does not have to move to takeanything



Functional layout which is suitable to the needs and convenience of the functionsperformed by the transforming resources within the processes In this layout, processesare organized by the type of work (function), similar machine, equipment andprocesses are grouped together, so the utilization of transforming resources isimproved Different products will have different needs and requirements; therefore,they take different routes to complete



A cell layout is one where the transformed resources entering the operation are selected (or pre-select themselves) to move to one part of the operation (or cell) inwhich all the transforming resources, to meet their immediate processing needs, arelocated After being processed in the cell, the transformed resources may go on toanother cell In effect, cell layout is an attempt to bring some order to the complexity

pre-of flow which characterizes functional layout



In product layout, machines, equipment and people are arranged in the way following

to the process of the product or group of related products

The decision as to which layout type can be adopted will be influenced by an

understanding of their relative advantages and disadvantages Table 2.1 shows:

Table 2 1 The advantages and disadvantages of four basic layout types

Source: Operations management book

2.1.3 The relationship between manufacturing process types and basic layout types

Process types present the approaches to the organization of processes and activities Layout has intimate relationship with process types Each layout type will be suited for

some process types, but it not rigid, there are often some overlaps between processtypes and the layouts We can mix flexibly these types of layouts and processes to

meet the actual needs As Figure 2.3:

Figure 2 3 The relationship between manufacturing process types and basic layout

is sick or traveling No one else is qualified or capable to take on that

employee's projects, causing a backlog of work until they return

 Long-term bottleneck: when problems occur continuously in the production

system and cause serious consequences For example: the inefficient of a working machine leads to the increase of quantity and waiting time of WIP on queue

2.2.3 Bottleneck detection methods

Ericson (2017) stated that there are four main methods to defined the bottleneck in asystem: analytically, discrete event simulation, using the data itself and manuallylooking at buffer levels:



This method is based on mathematical calculations giving the bottleneck (Yu and Matta,2014), by measure some data such as starving or blocking percentages The results of thismethod can be intuitive, satisfying However, it is very difficult to deploy because of thesophisticated of the production system (Leporis and Králová, 2010)



According to Ericson (2017), Simulation models are also popular method which havebeen used since 1980s When using this method, a model of the system is created intosimulation software and the model can run for custom periods of time The mainadvantage of this method is that it can export pretty detailed data about the productionfrom the software such as average stay time on queues, average queue sizes, utilization

of machines and equipment, statistics of failures and maintenance activities as well.Additionally, that it is easy to test new changes, experiment and see how they affectthe system However, simulation takes a lot of time to create and perform If there areany wrong assumptions can lead to a different result



Ericson (2017) stated that this method uses the data which is collected from themanufacturing system Applying data itself method helps user to save time, cost andeasily to conduct because of available information of manufacturing system Knowingthe bottleneck in real-time allow the industrial engineer to optimize it accordingly



One more practical approach is “The bottleneck walk” which was pointed out by Roser

et al (2015) In this method, a person walks around the process flow and look at bufferlevels in real-time to determine the bottleneck This is the easiest method to definedthe bottleneck in the system compared to data driven, analytical or simulation It helpsthe engineers or operators to use and detect the problems simply

2.2.4 Type of data for bottleneck analysis

Katana (2019) stated that there are 4 tactics can follow to detect the bottlenecks in thesystem

In the process steps, collecting unfinished products on queues and then defined whichqueue accumulates the most semi-products, so next step will be the bottleneck of thesystem

Collecting data about the increase of throughput of each workstations becausebottlenecks affect the throughput time, so if a machine is prone to bottleneck thethroughput will increase, and it’ll affect the overall production rate



Another way to analyses bottleneck is using data of machine utilization because each

of them always has a limit If there is no bottleneck in the production line, all machineswill operate at a similar capacity If it appears, one machine in the process will have towork at a higher capacity to deal with a long queue

Collect data of the average waiting time (AWT) of semi-product on queue is anotherway to identify the bottleneck in the production line because the station will be thebottleneck if its prior queue has the longest AWT stated by Law and Kelton (1991)

2.3 Modeling and Simulation

2.3.1 Modeling and Simulation definition

Panvan (2020) stated:

Modeling and simulation (M&S) is the use of a physical and logical representation

of a given system to generate data and help determine decisions or make predictionsabout the system M&S is widely used in the social, physical sciences, engineering,manufacturing and product development, among many other areas

Maria (1997) said that “Modeling is the process of producing a model; a model is arepresentation of the construction and working of some system of interest” It is usefulfor industries including manufacturing system because this model can predict theimpact of changes on the system To get high effectiveness, the model need to bedesigned approximately to the existing system Simultaneously, it shouldn’t be toocomplicated to make sure the model can be applied easily and clearly

This method helps researcher can modify and run experiment easily without too manyrisks because all of scenarios for the new model of system are deployed and performed

in a simulation software Dooley (2002) pointed out the strengths of Simulation

compared to others that “If other methods answer the questions What happened, and how, and why? simulation helps answer the question What if?”.

2.3.2 The purpose of Modeling and Simulation

There are seven applications of M&S in social science pointed out by Axelrod (1997)including: entertainment, theory discovery, training, education, prediction, proof, andperformance It can be applied for many areas: design and analysis of productioncontrol systems, production planning, determine productivity in production systems,production processes, material handling systems, logistics operations, manage anddetermine the policy of stocking and purchasing materials of the inventory system.However, this study is about simulation for mattress manufacturing system, so I onlyfocus on 3 of applications which are prediction, performance and proof

 Prediction: base on the design of existing model, the output data can be easilycollected From that, it helps to build new model for improvement and forecast how thefuture behavior of the new one, so that researchers can change, modify the model untilmeet their expectations and targets

 Performance: with an appropriately calibrated and validated model, simulationcan be used to perform real tasks for an organization, such as diagnosis or decision-making

 Proof: as an ability of prediction mentioned above, simulation can providevisual data for experiments, so it can be used to prove which solution is good and feasible

to persuade superiors to deploy

2.3.3 Modeling of manufacturing system

Modeling of manufacturing system requires understanding of the types ofmanufacturing processes including characteristics, issues, objectives which relate toeach type of process There are five types of manufacturing processes as mentioned inthe former section 2.2.1 including:

In manufacturing system modeling, there are some of characteristics which need to be

noticed to build up a model For more detail, they are presented in the Table2.2:

Table 2 2 Characteristics of a manufacturing system model

Source: Use of simulation in manufacturing and logistics systems planning by Heilala

(1999)

2.3.4 Simulation tool

There are a lot of commercial simulation tools available These tools can be classified into three groups, according to Heilala (1999)

General-purpose simulation language: The type of simulation tool requires the

people who use this tool to be a proficient programmer, expertise at simulation as well

Simulation front-ends: The simulation front-ends are essentially interface programs

between the user and the simulation language being used

Simulators: The simulators utilize constructs and terminology common to the

manufacturing community, and offer graphical presentation and animation This type

of simulation tool is simple and easier for user without adept in program

Currently, some of simulators software can easily find in the market such as:AutoMod, WITNESS, Arena, Promodel, Extend+MFG and Flexsim, and so on

2.3.4.1 Introduction of Flexsim software

As mentioned above, there are a lot of Simulation software in the market, but in thisthesis, Flexsim version 2019 is used for this study Flexsim is a discrete-eventsimulation software package based on Windows system developed by FlexsimSoftware Products, Inc This powerful software allows the user to build a 3D computersimulation model of a real-life system and run experiments on it It provides naturalframework for simulation modeling; conceptual guidance; automated gathering ofstatistics; graphic symbolism for communication; animation; and increasingly,flexibility to change the model More specifically, with Flexsim, the user can collectoutput data through charts, diagrams, tables, and data can even be exported to Excel,Word, CVS and other software supporting the study and analysis To improve theproductivity of production line, Flexsim is a suitable choice because it can show thewhole process with sufficient parts and detail, e.g., conveyor, operator, processor,queue, forklift Besides, experiments can be deployed on computer quickly, they can

be completed within a month, a week, or a few hours depending on the complexity ofthe model and the skill of the engineer Therefore, users can reduce the time and costrequirements compared with physical testing

Figure 2 4 A logo image of Flexsim software

Source: Flexsim.com

2.3.4.2 Advantages and disadvantages of Simulation

Heilala (1999) stated that there are some advantages and disadvantages of simulation

shown in the Table 2.3 Through the information in the table, we can realize how

effective the simulation is and these are some reasons why Simulation can be a goodchoice for manufacturing system analysis

Table 2 3 The advantages & disadvantages of Simulation

 Study the behavior of a system  Expensive: high investment onflexibly without building the software license

 Reduce manufacturing cost and model is long and complex.risk through thorough testing  Simulation cannot accuratescenarios by software

100%

 Results are visual in general,

 Require accurate boundarycompared to other model

conditions and input data

 Find out problems existing in

 It’s quite difficult to interpretthe system easily

the simulation results

 Simple to perform ``What-If''

analysis

Source: Use of simulation in manufacturing and logistics systems planning by Heilala

(1999)

21

CHAPTER 3: CURRENT PROBLEMS AND THE

IMPLEMENTATION OF MODELING & SIMULATION

OF THE ACTUAL MATTRESS PRODUCTION LINE

3.1 Mattress production process description

The manufacturing process of the company is batch processing Because of theattributes of mattress production, there are a lot of designs and size leading to hundreds

of mattress types In general, all mattresses have the same process, the differencesbetween them are size, materials, components and the way to make them, so theyrequire highly skilled workers To meet the characteristics of similar basic process andthe variety of products, the suitable layout for the manufacturing process of thecompany is a combination of functional and product layout to take the advantages ofboth types A combination layout is possible where an item is being made in differenttypes and sizes The main sequence of operation follows the product layout, but ineach section, machinery is arranged in a functional layout to meet the variety

In the mattress production system of Dunlopillo Vietnam Ltd, the production line isdivided into 3 major Sections including Cover, Spring and Finishing The process ofmaking a mattress has a series of steps as follow:

In the Spring Section: the spring frame of the mattress is created The first step in this

section is to produce coils from steel wire to create 3 types of spring mattress i.e.Bonnel, CPS and IPS Three types of coil are produced by 3 automatic Coilermachines At the following stage, coils for Bonnel Spring are assembled, bend helicalwithout border wire by semi-automated machine, coils for CPS Spring are assembledand folded into non-woven, coils for IPS Spring are cut and assembled as well Thisstage also includes 3 semi-automated machine Subsequently, assembled springs arearranged and clipped into border wire and stabilizer at 2 processing tables

In the Cover Section: parallel to the Spring Section, cover of the mattress is also

produced The cover comprises of 3 parts i.e Top, Bottom and Border To begin with,Cover is quilted by several layers consisting of fabric, PU, fiber and non-woven.Depending on the type of mattress, processing time, quantity and type of layers willvary The quilted cover is produced in 2 automated Quilting machines In the next,

quilted Border is sent to 1 cutting machine to cut into accurate size Top and Bottom is cutautomatically in the quilting machines After that, Top, Bottom, Border continuously aresent to a series of tailoring machine (including 2 panel hemming machines, 1 borderhemming machines, 1 embroidery border machine, 3 panel sewing machines, 5 bordersewing machines) to hem and sew (sewing labels, flysheet, rope, ) Finally, all of them

are checked by QC workers and transferred to Finishing Section to attach to the spring In the Finishing Section: this Section comprises of 4 steps as 4 stations: Glue-box, Tape-

edge, QC and Packaging Spring frame from Spring Section is transferred to glue-boxstation to glue with different layers of PU side, PU sheet, felt, latex on 4 Glue-boxprocessing tables Next, Glued mattress is inserted cover and taped edge manually by 4operators with 4 Tape-edge machines After this step, the mattress is almost finished, then

it is sent to QC station with 2 tables to check all dimension parameters, characteristic,

visual of Top, Bottom, Border following to “The Instruction of finished mattress quality inspection” from QA-QC department The process finishes with Packaging stage at a

processing table along with 2 workers

Figure 3 1 Mattress structure

Source: Author’s compilation

Figure 3 2 Mattress production process

Source: Author’s compilation

Due to the different characteristic and the capacity imbalances in Spring, Cover and

Finishing Section, working time for each Section is different and it is shown as Table 3.1 below:

Table 3 1 The working schedule

Except for CPSand IPS Coilermachine

*Working 6 days per week (from Monday to Saturday)

Source: Author’s compilation

3.2 Current problem description

3.2.1 Current production perspective

Currently, production is mainly for export Due to the bulky product size that takes a

lot of space to store and the variety types of products, the major business model is

MTO (Make to order) Besides, some big markets such as Malaysia, Singapore, China,

Hong Kong have large orders and have the certain number of key products, so the

company also combines MTS (Make to stock) as well to meet the needs of these

markets In recent years, the purchase order has been relatively stable within the

capacity, so production and business activities have been controlled quite well

According to Monthly Production Report (MPR) in 3rd quarter, 2020, the average daily

yield is approximately 138 mattresses More detail is shown in Table 3.2

Table 3 2 The average daily yield of mattress production system in third quarter, 2020

Source: Monthly production report

In general, the current quantity of finished goods can meet the domestic and foreign

orders When the machine has problems, any unexpected things occur that delay the

production schedule, or the number of orders increases, the company still handle and meet

the delivery schedule by adjusting its internal capability However, the production is not

really efficient, so it will be very hard to deal with unforeseen situations if there are more

orders Looking at the output in the Table 3.2, the problem here is balancing loss leading

to accumulation phenomenon: Finish Section compared to the remainders Moreover,

based on the MPR (Table 3.3), Production productivity rate of Finishing and Cover

Section are very low There are a lot of reasons can cause this problem such as low

resource utilization, inappropriate resource allocation leads to the appearance of

bottlenecks, problems in planning, or downtime of machinery, etc This matter ispretty serious which can make wasted resources and high cost Therefore, it need moredetailed analysis to define thoroughly what problems are actually happening in theprocess and what solutions are optimal to solve them.

At the DVL, the Production Productivity Rate (PPR) is calculated by formula:

ℎ

The Average Production Productivity Rate per day for three sections are show in the

Table 3.3 below.

Table 3 3 The Average Production Productivity Rate per day

Finished Goods (unit) Spring Unit (Bonnel, Matt Cover (set)

IPS & CPS)

Total Total PPR Total Total PPR Total Total PPR working cycle (%) working cycle (%) working cycle (%) hours time hours time hours time

(hour) (hour) (hour) (hour) (hour) (hour)

Source: Monthly production report

3.2.3 Future demand forecast

As mentioned briefly about the problem of the company in the Introduction Thecompany within the next 2 years when the Covid19 pandemic will be graduallycontrolled, the company will expand more its business in Vietnam and Indonesialeading to the demand forecast for the following 2 years will increase as shown in

Table 3.4 below.

Thus, the existing production capacity needs to be calculated and measured to optimizeproduction efficiency Then compare it with the forecast demand to determine howmuch the factory needs to produce more accurately? Is the current capacity enough tomeet the demand? If not, what solutions do the company need to take to improve?