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OPTIMIZATION OF MULTI-ECHELON SUPPLY CHAIN KANBAN MODEL USING GENETIC ALGORITHM MAHDI SABAGHI A project report submitted in fulfilment ofthe requirements for the award of the degree of master of engineering (Industrial Engineering) Faculty of Mechanical Engineering Universiti Teknologi Malaysia AUGUST 2011

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OPTIMIZATION OF MULTI-ECHELON SUPPLY CHAIN KANBAN MODEL

USING GENETIC ALGORITHM

MAHDI SABAGHI

A project report submitted in fulfilment ofthe

requirements for the award of the degree of

master of engineering (Industrial Engineering)

Faculty of Mechanical Engineering

Universiti Teknologi Malaysia

AUGUST 2011

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111

Dedicated to my beloved parents who have been a great source ofmotivation,

inspiration, and endless patience and encouragement when it was most required.

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IV

ACKNOWLEDGEMENT

I offer my sincerest gratitude to my supervisor, Dr Wong Kuan Yew who has

supported me throughout my thesis with his patience and knowledge. I attribute the

level of my Masters degree to his encouragement and effort and without him this

thesis, too, would not have been completed or written.

Besides, I am forever indebted to my father, who taught me that the best kind

of know ledge to have is that which is learned for its own sake encouragement and

my mother, who taught me that even the largest task can be accomplished if it is

done one step at a time.

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v

ABSTRACT

A supply chain system (SCS) consists of organizations or companies that

utilizes approaches to have an effective relation between suppliers, manufacturers,

warehouses, distribution centers, retailers and finally, the customers. Kanban system

is an efficient and easy system to be implemented. In a kanban system each plant

sends signals to the following plant for needed parts. The kanban withdraws parts

instead of pushing parts from one station to another station. The workstations are

located along the production lines and only produce or deliver desired components

when they receive a card. The number ofkanbans can significantly influence the load

balance between processes and the amount of orders suppliers need to obtain from

subcontractors. Large kanban size results in large amount of WIP inventory at each

workstation. On the other side, although reducing kanban size causes a decrease in

WIP inventory it leads to transportation increases as well as reduction in the system

throughput rate. In this study a multi-echelon supply chain system controlled by

kanban system, is considered. Decision making is based on determination of the

number of kanbans as well as economic-quantity order of products. Since the

adopted model used in this study is mixed integer non-linear programming (MINLP)

type and solving it by exact algorithm such as branch and bound (B&B) takes a lot of

time, a heuristic method via Genetic algorithm (GA) is presented. Some problems are

solved by our proposed GA to illustrate the performance of the method.

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VI

ABSTRAK

Satu sistem rantaian bekalan terdiri daripada organisasi atau syarikat-syarikat

yang menggunakan pendekatan untuk mempunyai hubungan yang berkesan antara

pembekal, pengilang, gudang, pusat pengedaran, peruncit dan akbir sekali,

pelanggan. Sistem kanban adalah sistem yang cekap dan mudah untuk dilaksanakan.

Dalam sistem kanban setiap pokok menghantar isyarat kepada organisasi berikut

bagi bahagian-bahagian yang diperlukan. Kanban menarik balik bahagian-bahagian

dan bukannya meno lak bahagian dari satu stesen ke stesen yang lain. Stesen kerja

yang terletak di sepanjang lini pengeluaran hanya mengemukakan atau menyerahkan

komponen yang diingini apabila mereka menerima kad. Bilangan kanban boleh

mempengaruhi beban di antara proses dan jumlah pesanan bekalan yang perlu di

dapatkan daripada subkontraktor. Saiz kanban yang besar okan memberi saiz

inventori WIP yang besar di setiap stesen kerja. Dari segi lain, walaupun

mengurangkan saiz kanban menyebabkan pengurangan dalam inventori WIP, ia

membawa kepada peningkatan pengangkutan serta pengurangan dalam kadar

pengeluaran sistem. Dalam kajian ini, satu multi rantaian bekalan sistem yang

dikawal oleh sistem kanban dipertimbangkan. Keputusan dibuat berdasarkan

penentuan bilangan kanban serta ekonomi-kuantiti pesanan produk. Oleh sebab

model yang digunakan dalam kajian ini adalah jenis pengaturcaraan bukan linear

campuran integer dan menyelesaikan ia dengan algoritma yang tepat seperti branch

and bound mengambil banyak masa, satu kaedah heuristik melalui algoritma genetik

telah dibangunkan. Beberapa masalah telah diselesaikan oleh algoritma ini untuk

menguji prestasinya.

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CHAPTER

TABLE OF CONTENTS

TITLE

VII

PAGE

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENT iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS vii

LIST OF TABLES x

LIST OF FIGURES xi

1 INTRODUCTION 1

1.1 Overview 1

1.2 Problem Statement 6

1.3 Objective 7

1.4 Scope of study 8

1.5 Significance of study 8

1.6 Study Outline 9

2 LITERATURE REVIEW 10

2.1 Introduction 10

2.2 Background 10

2.2.1 Supply Chain Systems 10

2.2.2 Just-in-Time (JIT) 13

2.2.3 Push / pull systems 16

2.2.4 Kanban 17

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2.3 Previous works on Kanban Models in Supply

Chain Systems

2.4 Chapter Summary

V111

21

25

3 RESEARCH METHODOLOGY 26

3.1 Introduction 26

3.2 Research Framework 27

3.3 Problem Formulation 28

3.4 Scenario of Multi-echelon Supply Chain

contro lled by Kanban 29

3.5 Problem Assumptions 30

3.6 Inventory Cost Calculations 31

3.6.1 Raw Material Inventory Characteristics 31

3.6.2 Work in Process Inventory Characteristics 33

3.6.3 Finished Goods Inventory Characteristics 35

3.7 Total Cost of the System 37

3.8 Genetic Algorithms 37

3.8.1 Components of a Genetic Algorithm 39

3.8.2 Selecting the Variables and the Cost

Function 40

3.8.3 Precision and Boundary Limits of Variables 40

3.8.4 Initial Population 40

3.8.5 Evaluation of Fitness 41

3.8.6 Stopping Criterion 42

3.8.7 Generating a New Population 42

3.8.7.1 Selection 43

3.8.7.2 Crossover 43

3.8.7.3 Mutation 44

3.9 Chapter Summary 44

4 MODEL FORMULATION

4.1 Introduction

4.2 The Kanban Model Formulation

46

46

46

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IX

4.2.1 Index and the definitions: 46

4.2.2 Parameters and the definitions: 47

4.2.3 Variables and the definitions: 48

4.3 The Cost of raw material inventory 49

4.4 The Cost of Work in Process (WIP) Inventory 51

4.5 The Cost of Finished Goods Inventory 55

4.6 The Total cost ofthe system 56

4.7 Case Study 60

4.8 Chapter Summary 62

5 RESULTS AND DISCUSSION 63

5.1 Introduction 63

5.2 GAsetup 63

5.2.1 Pilot Test 64

5.2.1.1 STEP 1 64

5.2.1.2 STEP 2 67

5.2.1.3 STEP 3 69

5.2.1.4 STEP 4 71

5.2.1.5 STEP 5 73

5.2.2 Final Solution 73

5.3 Performance 75

5.4 Chapter Summary 78

6

7

8

CONCLUSION AND RECOMMENDATION

6.1 Conclusion

6.2 Future Work

REFRENCES

APPENDIX

79

79

80

81

84

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TABLE NO

LIST OF TABLES

TITLE

x

PAGE

1.1 Different Meaning of Kanban and Plant 3

4.1 The data for system parameters 61

4.2 Solutions Using Branch & Bond 62

5.1 STEP 1: Boundary limits and Results of three replicates 65

5.2 STEP 1: GA Settings 65

5.3 STEP 2: Boundary limits and Results of three replicates 67

5.4 STEP 2: GA Settings 67

5.5 STEP 3: Boundary limits and Results of three replicates 69

5.6 STEP 3: GA Settings 69

5.7 STEP 4: Boundary limits and Results of three replicates 71

5.8 STEP 4: GA Settings 71

5.9 Final Test: Summary of Results 73

5.10 Optimal Solution and Cost Value 74

5.11 Comparison ofGA outputs and Solver 75

5.12 A four-Stage Kanban Supply Chain System and the results 75

5.13 A five-Stage Kanban Supply Chain System and the

Results 76

5.14 A six-Stage Kanban Supply Chain System and the Results 76

5.15 A seven-Stage Kanban Supply Chain System and the

Results 77

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FIGURE NO

LIST OF FIGURES

TITLE

Xl

PAGE

1.1 Primary Components in a Supply Chain 2

1.2 A typical supply chain system 3

2.1 Typical Supply Chain System (Beamon, 1999) 11

2.2 A typical supply chain system 12

2.3 Schematic representation ofthe push system 16

2.4 Schematic representation ofthe pull system 17

2.5 A multi-stage supply chain system with kanban operations 20

2.6 Kanban operation between "i" and" i+1" plants 20

3.1 Research framework 27

3.2 Schematic Multi-Stage Supply Chain System Operated

under Kanban Supervision 29

3.3 Schematic Kanban Stage i Formed by two Adjacent Plants

i and i+l 30

3.4 Schematic View of Raw Material Replenishment Operated

by Kanban 32

3.5 Schematic View ofWIP Inventory Characteristics

Operated by Kanban at Plant i 34

3.6 WIP inventory characteristics Operated by Kanban 35

3.7 Schematic View of Finished Goods Characteristics

Operated by Kanabn 36

3.8 Picture Overview of Genetic Algorithm 39

3.9 Initial Population Matrix 41

3.10 Schematic View of Linear combination Crossover 43

3.11 Schematic view of Mutation 44

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XII

4.1 Characteristics of raw material inventory 50

4.2 Characteristics of WIP inventory at stage i 52

4.3 Calculating the WIP average inventory at stage i 53

4.4 Characteristics offmished goods inventory 56

4.5 A three-stage supply chain system 61

5.1 Cost Function for STEP 1, replication 1 66

5.2 GA Variable Allocating for STEP 1, replication 1 66

5.3 Cost Function for STEP 2, replication 3 68

5.4 GA Variable Allocating for STEP 2, replication 3 68

5.5 Cost Function for STEP 3, replication 1 70

5.6 GA Variable Allocating for STEP 3, replication 1 70

5.7 Cost Function for STEP 4, replication 1 72

5.8 GA Variable Allocating for STEP 4, replication 1 72

5.9 Solution Results of GA and Solver 77

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CHAPTER 1

INTRODUCTION

1.1 Overview

To better compete in today's global markets, many cornpames have been

trying to improve system managements, increase product and service quality, and

reduce manufacturing and inventory costs. For this reason, many new production

strategies were developed such as: just-in-time manufacturing, lean manufacturing,

kanban systems, and total quality management to improve the supp ly chain

management goals. In a supply chain system, in order to minimize the total system's

costs and also to satisfy the service level requirements, the aim is to produce products

in right quantities and distribute them to right location, at right time. A supply chain

system (SCS) is a set of approaches that utilizes an effective relation between

suppliers, manufacturers, warehouses, distribution centers, retailers and finally, the

customers (Chopra and Meindl, 2010). There are three main components in any

supply chain system, given as manufacturers, wholesalers and retailers, as it is shown

in Figure 1.1 (Wang and Sarker, 2006). However, it doesn't mean to have all of the

three components in a SCS, necessarily. Depending on the integration of the

independent systems, some SCSs may contain only one component while others may

contain more than one. This research has focused on the current proposed optimal

method that is called Wang method (Wang and Sarker, 2006). The main goal of this

investigation is to enhance the performance of the current method. Since this method

has app lied only the manufacture component, the same status is also used in this

study.

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r---- ---------------------------------------------------------

Retail erswholesalers

f"------.. Primary components,-----,

Figure 1.1 Primary Components in a Supply Chain

The procedure in any manufacturing system is like this; at the first plant the

raw material from the suppliers is used in order to produce the semi-finished

products. Semi-finished products will be sent to the next plants for supplementary

processing, until they enter the last plant for final processing to finished products.

The manufacturing facilities of a company may be located at the same city, or at

different cities or in different states. In this case, there may be considerable material

flows between manufacturing facilities which is the consequence of the work-in­

process formed by the semi-finished products. The word plants in the study can refer

to companies, plants, workshops, workstations, or machines, and Kanban can be a

meaning for AVG (Automated Guided vehicle), truck, ship, train, cart, toe, and so

on, depending on the situation. Table 1.1 lists the different meanings ofkanban in

different types ofplants.

Proper on time delivery means that the goods should be delivered exactly

according to the ordered quantity on the right location. Generally there are two types

ofSCS:

(a) Single-stage supply chain system (SSSCS);

(b) Multi-stage supply chain system (MSSCS);

Generally the manufacturing system in the supply chain system has at least

two plants. If SCS consists of only two plants, it is called SSSCS, but if it consists of

more than two plants it is MSSCS. In this study, the focus of the investigation is on

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Multi-stage supply chain system (MSSCS). However the model can also be

conducted for SSSCS problem.

Table 1.1 Different Meaning of Kanban and Plant

KanbanPlant Type Locations Transportation

Transporters

Workstations or AGV, fork-lifter,Sliop Intra House

work centers toe, trolley

Workstations or fork-lifter, toe,Plant Inter House

work centers trolley

Plants orPlant or Company Intra or Inter Cities Truck, Train, Ship

Companies

Plants or Truck, Train, Ship,Plant or Company Inter States

Companies Air-cargo

Companies Countries CompaniesTruck, Train, Ship,

Air-cargo

In a typical supply chain system, as it is drawn in figure 1.2, the flow of

material is downward (from supplier to customer), on the contrary, the flow of

information is upward, from customer to supplier.

Material flow

•r···.·-------- ----·---··--······--··---·---·---··. ·· ··.._-----

Retailer sMM

Manu facturers

=~ill}-~TI-+~ Whtlksa lcrs

r - - - - - -" Primary com ponents

,------

•lnformatlon no\\. '

Figure 1.2 A typical supply chain system

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Wang and Sarker (2006) have categorized the main operational activities of a

supply chain system in order to reflect the basic movement of goods, services, and

information in an integrated supply chain system. According to them, these activities

are:

(1) Raw materials: sales forecasting, inventory planning, and purchasing,

transportation between suppliers and manufacturers,

(2) Work-in-process: processing and managing efficiently the inventories of

partially completed products inside the manufacturing plants,

(3) Finished goods: warehousing of finished goods inventory, servicing the

customers, and transporting materials among the who lesalers, retailers, and

customers.

In this study, the focus is on these three activities, in order to optimize the

total cost ofthe system.

In any supply chain, transportation of materials plays an important role in the

system cost. For most firms, transportation is the single highest cost in distribution,

usually accounting for 30% to 60 % of distribution cost (Arnold and Chapman,

2001). A supply chain system which is operated with slow transportation is not

effective and indicates poor planning, poor communication and insufficient quality

levels. In order to remain competitive in the global market, every organization has to

focus on increasing productivity, alacrity response to customers, and raising the

standards of efficiency. Considering this vital role that transportation plays in the

system, managers should be more concerned about that.

Just in Time (lIT) manufacturing was first developed by Taiichi Ohno for

Toyota manufacturing plants in order to respond to consumer demands with

minimum delays. Major component of JIT philosophy is the kanban information

system which is described in detail by Monden (1993). The objective for

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implementing kanban in a system is to reduce the transportation cost in order to

increase the productivity and feasibility ofthe system.

In a Supply Chain System, the material flow and information flow between

two adjacent plants form a kanban stage. The kanban system is an element of just-in­

time (lIT) system that has captured the most attention of researchers. Kanban is a

Japanese word that means "visible sign" or card (Gupta et al., 1999). Gupta et al.

described the kanban as an information system which contains some information

such as kanban type, component name and number, the station location and the

destination station. They mentioned that this kanban system can improve the ability

of the system in controlling production and also simplicity in scheduling production,

alleviating the force on workers, easily identifying the parts by means of kanbans

which attached to the containers and reducing the volume of paper work. Numerous

companies have incorporated kanban procedures into their systems and have

demonstrated that it is a simple and effective method for implementing JIT

philosophy. For testifying the significance of kanban, according to Gupta et al

(1999), since 1977 a large number of manufacturing companies in the USA have

either implemented the JIT system or were seriously considering implementing it.

Kanban systems are normally applied to systems with reliable processes, low

set-up times, static demand, and sufficient capacity. It helps companies to maintain

production flexibility and responds quickly to minor changes in demand. With these

capabilities, kanban systems carry small amounts of safety stock inventories, whilst

meeting customer service objectives and requiring simple control systems (Monden,

1993).

In kanban systems, various factors such as the total number of kanbans,

transportation sizes (container size), and safety storage sizes have influence on the

efficiency of the manufacturing systems (Paris and Pierreval, 2001). For example,

the total number ofkanbans can control the inventory levels. Iftoo many kanbans are

used, it would result in large amount of work-in-process inventory at each

workstation. On the contrary, reduction of the number of kanbans will cause lower

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work-in-process inventory; however it leads to a downfall in the system throughput

rate (Savsar and Choueiki, 2000).

In this study, Kanban system is used to control SCS for achieving goals. The

supply chain system considered in this study consists of three parts: the suppliers,

manufacturers, and retailers. In the supply chain systems, the deliveries of raw

material from the suppliers, the work-in-process (WIP) in production stage, and the

finished goods to retailers are all controlled by the Kanbans. Determination of the

number of Kanbans and batch sizes between two plants to approach the JIT

production philosophy are the important factors in this study.

1.2 Problem Statement

Due to the rising cost of manufacturing and transportation costs, enterprises

have shown an increasing attention for effective supply chain management. Efficient

supply chain management can lead to decrease in production cost, inventory cost and

transportation cost. This would results in improvement of customer service

throughout at the stages that are all invo lved in the chain.

As it has been stated earlier there are two kinds of supply chain systems;

Single stage supply chain system (SSSCS) and Multi stage supply chain system

(MSSCS). SSSCS is the sort which there is just two plants in the supply chain

system. In this system the demand is received in the finished goods stage (second

stage), since the goods are produced in manufacturing stages, and the raw material is

replenished in the raw material stage (supplier). In this system the WIP just happen

between these two plants. In MSSCS there are more than two plants in the system

and the products manufactured in intermediate stages. The demand receives in the

finished goods stage and raw material rep lenishments happen at the raw material

stage. The WIP occurs in each two adjacent plants. The material and information

flow between each two adjacent stage compose a Kanban stage.

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The series of questions that come to mind in this area are:

(i) How the WIP inventories should be controlled and optimized in order to

minimize the cost ofthe system?

(ii) What is the ordering plan for the suppliers III order to procure raw

material?

(iii) What is the delivery policy for the retailers at the finished good stage for

dispatching the finished goods?

Supply chain systems controlled by Kanban mechanisms are naturally easier

to control. Moreover, it is necessary to consider about submitted models for Kanban

mechanism for estimation of Kanban supply chain parameters. This study presents a

model in supply chain system with regard to costs under just in time (JIT) philosophy

(Wang and Sarker, 2006). Since the model is mixed integer non-linear programming

(MINLP) type and solving it by exact algorithm such as branch and bound (B&B)

takes a lot of time, and as the larger the size of the problem, the harder to solve the

problem optimally. Thus, the following questions must be considered to enhance the

model performance and throughput.

(i) How to optimize the Kanban supply chain model to make a successful

decision?

(ii) How to optimize the proposed Kanban supply chain system to reduce the

calculation time?

1.3 Objective

Controlling the production and reducing work-in-process (WIP) in supply

chain system is an effective way in order to minimize the total cost of the system.

The Kanban operation system is to be configured based on the optimal results of the

model. The general objectives of this study are given as following:

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(i) To find the optimal number of Kanbans and the batch size in each stage

as well as the total quantity of production over one period in a supply

chain system.

(ii) To evaluate and compare the obtained results of the proposed model with

Branch and Bound (B&B), in order to understand the performance of

current model in solving Kanban models.

1.4 Scope of study

The supply chain system considered in this study consists of three parts: the

suppliers, manufacturers, and retailers. (a) The raw material, the input; (b) The

manufacturing system, the work-in-process, and; (c) The finished good part, the

output. In the supply chain systems, the deliveries of raw material from the suppliers,

the work-in-process (WIP) in production stage, and the finished goods to retailers are

all controlled by the Kanbans.

The manufacturing system III the supply chain has at least two plants

(MSSCS).

In order to optimize the Kanban supply chain model genetic algorithm IS

developed and Matlab tool is implemented in order to solve the proposed model.

1.5 Significance of study

Since the kanban numbers influence the product inventory level it is very

crucial for managers to determine the number of Kanbans used in the system. In

addition, the number of Kanbans can extensively influence the load balance between

processes and the amount of orders suppliers need to obtain from subcontractors.

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The MSSCS controlled by kanbans can be applied to many places. The

production companies that deal with the supp liers and retailers and their products'

processes are finished in more than two steps; indeed, the WIPs can be shipped in

batches. Good examples can be found in the automobile industry, oil industry,

grocery supply chain, furniture companies, electronics product companies, or apparel

production companies etc. If using the kanban technique, the amount of WIP

material, the batch size and the number of batches, and kanban numbers between

every two processes in a production cycle are to be determined.

1.6 Study Outline

The background of the problem and some of the concepts described in

Chapter 1 provided an introduction to the supply chain system operated under JIT

principle by Kanban technique. Chapter 2 presents a literature review on supply

chain, lIT philosophy, push and pull systems, and Kanban technique which has been

applied to the production. Research framework and the methodology to solve the

problem, architecture and solution strategies of the proposed genetic-based algorithm

method to solve the problem are presented in Chapter 3. Chapter 4 is about the

formulation of the Kanban model in multi stage supply chain systems. Next, in

Chapter 5, the optimized kanhan numbers and batch size quantity are obtained by

using Matlab tool to solve the problem and evaluate the obtained results. The

research summary, conclusions, and recommendations for future research can be

found in Chapter 6.

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