Production Efficiency Improvement For Production Line Of Mass Production : A Case Study Using Poka Yoke Concepts.
PRODUCTION EFFICIENCY IMPROVEMENT FOR
PRODUCTION LINE OF MASS PRODUCTION: A CASE
STUDY USING POKA YOKE CONCEPTS
ROHAIDA BINTI YUSUFF
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UNIVERSITI TEKNIKAL MALAYSIA MELAKA
PRODUCTION EFFICIENCY IMPROVEMENT FOR
PRODUCTION LINE OF MASS PRODUCTION: A CASE STUDY
USING POKA YOKE CONCEPTS
This report submitted in accordance with requirement of the Universiti Teknikal Malaysia Melaka (UTeM) for the Bachelor Degree of Manufacturing Engineering
(Manufacturing Management) with Honours.
by
ROHAIDA BINTI YUSUFF
FACULTY OF MANUFACTURING ENGINEERING 2009
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UTeM Library (Pind.1/2007)
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
BORANG PENGESAHAN STATUS LAPORAN PSM
JUDUL: PRODUCTION EFFICIENCY IMPROVEMENT FOR PRODUCTION LINE OF MASS PRODUCTION: A CASE STUDY USING POKA YOKE CONCEPTS
SESI PENGAJIAN: Semester 2 (2008/ 2009)
Saya ROHAIDA BINTI YUSUFF
mengaku membenarkan laporan PSM / t esis (Sarj ana/ Dokt or Falsaf ah) ini disimpan di Perpust akaan Universit i Teknikal Malaysia Melaka (UTeM) dengan syarat -syarat
kegunaan sepert i berikut :
1. Laporan PSM / t esis adalah hak milik Universit i Teknikal Malaysia Melaka dan penulis.
2. Perpust akaan Universit i Teknikal Malaysia Melaka dibenarkan membuat salinan unt uk t uj uan pengaj ian sahaj a dengan izin penulis.
3. Perpust akaan dibenarkan membuat salinan laporan PSM / t esis ini sebagai bahan pert ukaran ant ara inst it usi pengaj ian t inggi.
4. *Sila t andakan (√) SULIT
TERHAD
TIDAK TERHAD
(Mengandungi maklumat yang berdarj ah keselamat an at au
kepent ingan Malaysia yang t ermakt ub di dalam AKTA RAHSIA RASMI 1972)
(Mengandungi maklumat TERHAD yang t elah dit ent ukan oleh organisasi/ badan di mana penyelidikan di j alankan)
(TANDATANGAN PENULIS)
Alamat Tet ap:
1205 Jalan Pasir Panj ang 21100 Kuala Terengganu Terengganu Darul Iman
Tarikh: 11/ 05/ 2009
(TANDATANGAN PENYELIA)
Cop Rasmi:
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FAKULTI KEJURUTERAAN PEMBUATAN
Rujukan Kami (Our Ref) : 15 Oktober 2012
Rujukan Tuan (Your Ref):
Pust akawan
Perpust akaan Universit i Teknikal Malaysia Melaka (UTeM) Taman Tasik Ut ama, Hang Tuah Jaya,
Ayer Keroh, 75450, Melaka
Saudara,
PENGKELASAN LAPORAN PSM SEBAGAI SULIT/ TERHAD
- LAPORAN PSM SARJANA MUDA KEJURUTERAAN PEMBUATAN (PENGURUSAN PEMBUATAN): ROHAIDA BINTI YUSUFF
TAJUK: PRODUCTION EFFICIENCY IMPROVEMENT FOR PRODUCTION LINE OF
MASS PRODUCTION: A CASE STUDY USING POKA YOKE CONCEPTS
Sukacit a dimaklumkan bahawa t esis yang t ersebut di at as bert aj uk
“ PRODUCTION EFFICIENCY IMPROVEMENT FOR PRODUCTION LINE OF MASS PRODUCTION: A CASE STUDY USING POKA YOKE CONCEPTS
” mohon
dikelaskan sebagai t erhad unt uk t empoh lima (5) t ahun dari t arikh surat ini memandangkan ia mempunyai nilai dan pot ensi unt uk dikomersialkan di masa hadapan.
Sekian dimaklumkan. Terima kasih.
“ BERKHIDMAT UNTUK NEGARA KERANA ALLAH”
Yang benar,
……….
EN. AB. RAHMAN BIN MAHMOOD Pensyar ah,
Fakult i Kej urut eraan Pembuat an
Universit i Teknikal Malaysia Melaka(UTeM) Karung berkunci 1200, Ayer Keroh,
75450, Melaka 06-2332546
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
Karung Berkunci 1200, Ayer Keroh, 75450 Melaka Tel : 06-233 2421, Faks : 06 233 2414
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DECLARATION
I hereby, declared this report entitled Production Efficiency Improvement for Production Line of Mass Production: A Case Study Using Poka Yoke Concepts is the result of my
own research except as cited in references.
Signature : ………..
Author’s Name : …ROHAIDA BINTI YUSUFF……….
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APPROVAL
This report is submitted to the Faculty of Manufacturing Engineering of UTeM as a partial fulfillment of the requirements for the degree of Bachelor of Manufacturing Engineering (Manufacturing Management) with Honours. The member of the supervisory committee is as follow:
(Signature of Supervisor)
……… (Official Stamp of Supervisor)
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ABSTRACT
Producing high quality of products and services is one of the key concerns in order to keep up with the competition in the global markets. Companies are putting a great effort on preventing customers from receiving faulty products and services by any means. However, the total elimination of mistakes in manufacturing processes has always been a great challenge for quality management. In this project, the applicability of Poka Yoke methodology in reducing the number of quality failures at Hicom Engineering Sdn.Bhd has been studied. Poka Yoke stands for the mistake proofing and is mainly developed for the purpose of eliminating human errors in manufacturing process. This project focuses on introduction and implementation of Poka Yoke concept to a selected production line at Hicom Engineeering Sdn.Bhd to improve the degree of quality performance and production efficiency by eliminating miss loading using Poka Yoke concept. Due to time constrain the profound investigation on production efficiency improvement was not made. A simulation to test the reliability of the device was made and result has shown a positive out come of the system.
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ii
ABSTRAK
Penghasilan produk dan perkhidmatan yang berkualiti merupakan satu kunci kejayaan yang menjamin kemenangan persaingan dalam pasaran dunia. Syarikat mestilah memerlukan usaha yang kuat bagi mengelakkan pelanggan mereka mereka daripada mengalami masalah dari segi produk dan perkhidmatan yang diberikan dalam semua aspek. Walaubagaimanapun, jumlah pengurangan dalam melakukan kesalahan dalam proses pengeluaran merupakan satu cabaran dalam pengurusan kualiti. Dalam menyiapkan projek ini, konsep ‘Poka Yoke’ telah dipelajari dan digunakan dalam mengurangkan jumlah kualiti produk yang tidak memenuhi kehendak pelanggan Hicom Engineering Sdn.Bhd. ‘Poka Yoke’ bermaksud penambahbaikan dan konsep ini diamalkan untuk mengurangkan kesilapan dalam menjalankan tugas akibat kecuaian manusia semasa proses pengeluaran. Projek ini bertumpu pada konsep pengenalan dan perlaksanaan ‘Poka Yoke’ pada satu jenis produk yang telah dipilih untuk memperbaiki perlaksanaan kualiti dan kecekapan kualiti dengan mengurangkan salah pasang produk pada mesin dengan menggunakan konsep ‘Poka Yoke’. Untuk menyiapkan projek ini, satu simulasi telah dibuat untuk menguji kebolehan alat tersebut dan ia telah memberi keputusan yang baik pada sistem.
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DEDICATION
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iv
ACKNOWLEDGEMENT
This project and the writing of this report has been a culmination for my studies in Universiti Teknikal Malaysia Melaka (UTeM). Many challengers have been faced during this project but at the same time it has been very interesting and rewarding.
Now that I am finishing this project, I would like to express my gratitude especially to my supervisor, Mr. Ab. Rahman bin Mahmood, for his constructive comments, ideas, support and guidance throughout this project.
Besides that, I would like to give my warmest thanks to the various people in the case company, Hicom Engineering Sdn.Bhd who have contributed to this work. Without your valuable and professional comments and criticism and outright support this wouldn’t have been possible.
Finally, many thanks to my family and all my friends for their endless support and energy they have given me during my studies.
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TABLE OF CONTENT
Abstract i
Abstrak ii
Dedication iii
Acknowledgement iv
Table of Content v
List of Tables viii
List of Figures ix
List of Abbreviation x
1. INTRODUCTION
1.1 Background 1
1.1.1 History of Poka Yoke 1
1.1.2 Company Background 2
1.2 Problem Statement 3
1.3 Objectives 3
1.4 Scope of Project 4
2. LITERATURE REVIEW
2.1 Definition and History of Poka Yoke 5
2.2 Errors and Defects in Poka Yoke 7
2.2.1 Human Error Classification 8
2.2.2 Classifying Mistakes 9
2.2.3 Root Cause Analysis 10
2.3 Inspection Techniques in the Field of Quality Control 13
2.3.1 Informative Inspection 14
2.3.2 Source Inspection 16
2.4 Types of Poka Yoke Devices 17
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vi
2.5.1 Characteristics of Poka Yoke 21
2.5.2 Process Deviation and Value Differences 21
2.6 Goal of Poka Yoke 22
2.7 Zero Quality Control 23
2.8 Company-Wide Poka Yoke 24
2.9 Implementations Process of Poka Yoke 24
2.10 Objectives of Poka Yoke Implementation 27
2.11 Characteristics of Quality Control Methods 28
2.12 Quality Costs and Mistake Proofing 29
3. METHODOLOGY
3.1 Flow Chart Explanation 32
3.1.1 Start 32
3.1.2 Define the Problem Statement, Objectives and Scope 32 3.1.3 Finding Literature Review; Books, Journal and Articles 33
3.1.4 Observation of Current Production 33
3.1.5 Collecting and Analyzing Miss Loading Data 33 3.1.6 Designing and Recommendation of Improvement Proposal 33
3.2 Gantt Chart 34
4. RESULT AND DISCUSSION
4.1 Introduction 35
4.2 Current production 36
4.3 Data Collection 39
4.4 Process Improvement 42
4.4.1 Experiment of Workability of the Device 43
4.4.2 Conclusion of the Experiment 47
4.5 Circuit Diagram 48
4.6 Schematic Diagram 50
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5. CONCLUSION 53
REFERENCES 55
APPENDICES
A Gantt Chart of PSM I B Gantt Chart of PSM II C Schematic Drawing
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viii
LIST OF TABLES
2.1 Classification of Human Errors 8
2.2 Classification Methods of Mistakes 10
2.3 Tool Summary for Root Cause Analysis 11
4.1 Data Rejection Cause of Miss-loading in Year 2008 39 4.2 Workability of the Poka Yoke Device in a Different Gap 44
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LIST OF FIGURES
2.1 Three Possible States of Mistakes with Three Functions of Poka Yoke 19
2.2 Poka Yoke for Assembly 23
2.3 Framework of Implementation Process 25
2.4 Mistake-Proofing Levels 26
3.1 Process Flow Chart 31
4.1 Exhaust Manifold Campro 37
4.2 Jigs Before Hold the Products 38
4.3 All Products Tie at the Jigs 38
4.4 Numbers of Product Rejects in 2008 40
4.5 Percentage of Product Rejects in 2008 40
4.6 Fishbone Diagram Illustrating Possible Defect Causes 41
4.7 Poka Yoke Device 43
4.8 Gap between the Product and Jig Block at 0.5 mm 45
4.9 No Gap between the Product and Jig Block 46
4.10 Gap between the Product and Jig Block at 0.8 mm 47
4.11 Circuit Diagram 49
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x
LIST OF ABBREVIATION
HICOM - Hicom Engineering Sdn. Bhd
Mm - Milimeter
Pcs - Pieces
PSM - Projek Sarjana Muda Sdn.Bhd - Sendirian Berhad
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CHAPTER 1
INTRODUCTION
This chapter introduces the background for the project, defines the problem statement, set objectives and scope for this study. An overall structure of this project is also provided.
1.1 Background
1.1.1 History of Poka Yoke
Poka Yoke was coined in Japan during the 1960s by Shigeo Shingo who was one of the industrial engineers at Toyota. Shigeo Shingo is also credited with creating and formalizing Zero Quality Control (Poka Yoke techniques to correct possible defects plus source inspection to prevent defects equals zero quality control).
Originally described as Baka-yoke, but as this means “idiot- proofing” the name was changed to the milder Poka Yoke. Poka yoke pronounced “POH-kah YOH-keh” means “fail-safing” or “mistake proofing”. Avoiding (yokeru) inadvertent errors (poka) is a behavior-shaping constraint or a method of preventing errors by putting limits on how an operation can be performed in order to force the correct completion of the operation. Where this is not possible, Poka Yokes perform a detective function, eliminating defects in the process as early as possible.
In 1963, a worker at Arakawa Body Company refused to use baka-yoke mechanisms in her work area, because of the term’s dishonorable and offensive connotation. Hence, the
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2
term was changed to Poka Yoke, which means ‘mistake-proofing’. Ideally, Poka Yokes ensure that proper conditions exist before actually executing a process step, preventing defects from occurring in the first place. Where this is not possible, Poka Yoke perform a detective function, eliminating defects in the process as early as possible.
1.1.2 Company Background
Hicom Engineering is a member of DRB-HICOM group of companies, offering state-of-art manufacturing capabilities to our customers. Hicom Engineering manufacture, machine precision castings and assemble components for automotive and general engineering purposes. Located in Selangor, Malaysia, Hicom Engineering was commissioned in 1991 with a total paid-up capital of USD8.07 million and a total investment of over USD18.4.
As one of Malaysia's leading manufacturers of cast-iron automotive components, we have a strong commitment to constantly improve the quality of our products. The MS ISO 9002 certification has only enhanced our commitment. Utilize the latest technological advances in support of our commitment to continuous improvement and provide the highest quality castings.
Hicom Engineering employs a diverse group of dedicated individuals with extensive experience in foundry and machining. Our employees are committed to the growth of the company and to achieving consistent quality for every Hicom Engineering product. Everyone at Hicom Engineering is responsible for his/her contribution to total quality that is a result of a unified approach at providing our customers with products that meet and exceed their expectations.
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1.2 Problem Statement
Poka Yoke is a method of preventing errors by putting limits on how an operation can be performed in order to force the correct completion of the operation. It can perform a detective function, eliminating defects in the process as early as possible. From this method, it can improve the production efficiency. The factor that effect the production efficiency are cycle time, loading and unloading time, machine breakdown, absenteeism, shortages of materials, down time of machine include machine setting, tool setting, parameter setting and quality problems, as well as factors that are outside the control of the operation manager.
At HICOM Engineering Sdn.Bhd, the problems of miss-loading occur frequently due to full-proof system was not incorporated to the production jigs. This lead to occurrence of product rejects and machine down time as a result of miss-loading. To solve this problem, many company implements this full-proof concept that called Poka Yoke. Evidence shows, it have a lot of improvement after the implementation of that system.
1.3 Objectives
The objectives of this study are:
1. Tostudy a Poka Yoke concept to improve production line at Hicom Engineering
Sdn.Bhd.
2. To improve the degree of quality performance and production efficiency by
eliminating miss-loading using Poka Yoke concept.
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4
1.4 Scope of Project
This project focuses on introduction and implementation of Poka Yoke concept to a selected production line at Hicom Engineering Sdn.Bhd. This research merely focuses on a production jig used for manufacturing of one kind of automotive component. Based on previous industrial experience by many companies, it is strongly believed that the reject rate will be reduced when there is no more part miss-loading cases. Ultimately, the production efficiency will increase when there is no more down time spent for producing defective parts that caused by miss-loading, machine setting time and jig setting-time.
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CHAPTER 2
LITERATURE REVIEW
This chapter introduces a theoretical background of Poka Yoke methodology. Besides that, it was focuses on the literature review of introduction and implementation of Poka Yoke concept to a selected production line at Hicom Engineering Sdn.Bhd.
2.1 Definition and History of Poka Yoke
Poka Yoke is a process improvement that improves visibility on the occurrence of defects, equipment, abnormalities and safety hazards for fast analysis and solution. Its purpose is to provide some intervention device or procedure to eliminate the possibility of a mistake or at worst case to catch it before it is transitioned into the next level of product or consigned to nonconforming product. Other than eliminating possibility for errors, mistake proofing is relatively inexpensive to install. Poka means inadvertent error and Yoke means prevention. Poka Yoke is implemented using simple low cost mistake proofing devices that detect abnormal situations before they occur or once they occurred stop production to prevent defects (Shingo, 1985).
Poka Yoke reduces the physical and mental burden of constantly checking for common errors that lead to defects such as missing process steps, process errors, miss set work pieces, missing or wrong parts, improper equipment set ups and so forth. A good Poka Yoke must be simple and low maintenance, very reliable, low cost, and designed for the specific workplace condition. When a Poka Yoke detects an error, it should either shutdown production or delivers a warning. Warning Poka Yokes should be used if the
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stopping of the line in the middle of a process increases the potential for defects. An effective Poka Yoke must inspect 100 percent of the items and provide immediate feedback for countermeasures (Shingo, 1985).
It was year 1961 when Shigeo Shingo, an industrial engineer at Toyota Motor Corporation introduced the concept of Poka Yoke. Based on Shingo’s long term experience and observation, he developed the concept of Poka Yoke and turned it from the idea into a formidable tool; a tool for achieving zero defect and eventually eliminating the need of quality control inspections. Since then, “Poka Yoke” has been an integral part of Japanese quality and manufacturing systems (Shimbun, 1988).
In its early days, term Poka Yoke was known as baka-yoke, meaning fool proofing. In the operator’s point of view, this term wasn’t very attractive, because of terms have dishonorable and offensive connotation. Soon after the name episode in one of the Japanese car manufacturing plants in 1963, the term to describe this methodology was changed to Poka Yoke. The term “Poka Yoke” stands for mistake proofing; referring originally devices, which serve to prevent the sort of inadvertent mistakes that anyone can make (Manivannan, 2006).
Many definitions for Poka Yoke can be found from the literature. The following statement describes best the idea of Poka Yoke from different aspects:
1. “The original idea behind Poka Yoke is to respect the intelligence of workers. Poka Yoke are for freeing worker’s time and mind to pursue more creative and value adding activities” (Shimbun, 1988).
2. “Error proofing is not so much a lean “tool” as it is a way of thinking and
evaluating problems. It is based on a philosophy that people do not intentionally make mistakes or perform the work incorrectly, but for various reason mistakes can and do occur” (Meier, 2006).
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Poka Yokes were originally developed for manufacturing, considered primarily physical devices to prevent mistakes from occurring. Nowadays the whole concept of Poka Yoke has a much more extensive purpose; it can be seen as a tool, as an effective quality control technique and finally as a quality philosophy. The basic principle behind all these "levels" is the prevention of defects. The creator of Poka Yoke concept, Shigeo Shingo, believed that defects could simply be eliminated in the first place, instead of relying on measures taken on after-the-fact. According to Shingo (1986), mistakes that lead to defects can be engineered out of the processes and defects can be eliminated this way. The well-known quality guru, Edward Deming, has once stated that "quality comes not from inspection, but from improvement of the process" (Manivannan, 2006). This statement is also the heart of the Poka Yoke philosophy. Rather than looking for defects, a true goal is to create processes that yield zero defects (Manivannan, 2006).
2.2 Errors and Defects in Poka Yoke
In order to have a thorough understanding of Poka Yoke, an understanding of why mistakes occur and what human factors make mistakes less likely is appropriate (Stewart & Grout, 2001). In addition, discussion of what do the words "mistake", "defect" and "error" mean in the context of Poka Yoke is provided. Shingo has made a clear distinction between a mistake and a defect. Mistakes are inevitable; people are human and cannot be expected to concentrate all the time, or always understand completely the instructions they are given. Defects results from allowing a mistake to reach the customer, and are thus entirely avoidable (Fisher, 1999).
Manivannan (2007) defines that a defect is any deviation from product specifications
that may lead to customer dissatisfaction. To be considered defective, the product must deviate from manufacturing or design specifications, and it must not meet the expectations of internal or external customers. According to Shingo (1986) the causes of defects lie in worker errors, and defects are the results of neglecting those errors. It follows that mistakes will not turn into defects if worker errors are discovered and
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8
eliminated beforehand. On the other hand, from the source inspection’s point of view, Shingo (1986) states that defects arise because errors are made and these two have a cause-and-effect relationship. Errors will not turn into defects if feedback and action takes place at the error stage.
2.2.1 Human Error Classification
Shimbun (1988) classifies ten different kinds of human errors, which are presented in table 2.1. Also Grout (1995) states about mistakes that to error is human. According to these, we will sooner or later come to the conclusion that almost all defects are caused by human errors.
Table 2.1: Classification of Human Errors (Shimbun, 1988).
TYPE OF HUMAN ERROR EXAMPLE
Forgetfulness Sometimes we forget things when we are
not concentrating.
Errors due misunderstanding Sometimes we make mistakes when we
jump to the wrong conclusions before we are familiar with the situation
Errors in identification Sometimes we misjudge a situation
because we view it too quickly or are too far away to see it clearly
Errors made by amateurs Sometimes we make mistakes through lack
of experience.
Willful errors Sometimes errors occur when we decide
that we can ignore rules under certain circumstances.
Inadvertent errors Sometimes we are absentminded and make
mistakes without knowing how they are happened.
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1.2 Problem Statement
Poka Yoke is a method of preventing errors by putting limits on how an operation can be performed in order to force the correct completion of the operation. It can perform a detective function, eliminating defects in the process as early as possible. From this method, it can improve the production efficiency. The factor that effect the production efficiency are cycle time, loading and unloading time, machine breakdown, absenteeism, shortages of materials, down time of machine include machine setting, tool setting, parameter setting and quality problems, as well as factors that are outside the control of the operation manager.
At HICOM Engineering Sdn.Bhd, the problems of miss-loading occur frequently due to full-proof system was not incorporated to the production jigs. This lead to occurrence of product rejects and machine down time as a result of miss-loading. To solve this problem, many company implements this full-proof concept that called Poka Yoke. Evidence shows, it have a lot of improvement after the implementation of that system.
1.3 Objectives
The objectives of this study are:
1. Tostudy a Poka Yoke concept to improve production line at Hicom Engineering Sdn.Bhd.
2. To improve the degree of quality performance and production efficiency by eliminating miss-loading using Poka Yoke concept.
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1.4 Scope of Project
This project focuses on introduction and implementation of Poka Yoke concept to a selected production line at Hicom Engineering Sdn.Bhd. This research merely focuses on a production jig used for manufacturing of one kind of automotive component. Based on previous industrial experience by many companies, it is strongly believed that the reject rate will be reduced when there is no more part miss-loading cases. Ultimately, the production efficiency will increase when there is no more down time spent for producing defective parts that caused by miss-loading, machine setting time and jig setting-time.
(3)
CHAPTER 2
LITERATURE REVIEW
This chapter introduces a theoretical background of Poka Yoke methodology. Besides that, it was focuses on the literature review of introduction and implementation of Poka Yoke concept to a selected production line at Hicom Engineering Sdn.Bhd.
2.1 Definition and History of Poka Yoke
Poka Yoke is a process improvement that improves visibility on the occurrence of defects, equipment, abnormalities and safety hazards for fast analysis and solution. Its purpose is to provide some intervention device or procedure to eliminate the possibility of a mistake or at worst case to catch it before it is transitioned into the next level of product or consigned to nonconforming product. Other than eliminating possibility for errors, mistake proofing is relatively inexpensive to install. Poka means inadvertent error and Yoke means prevention. Poka Yoke is implemented using simple low cost mistake proofing devices that detect abnormal situations before they occur or once they occurred stop production to prevent defects (Shingo, 1985).
Poka Yoke reduces the physical and mental burden of constantly checking for common errors that lead to defects such as missing process steps, process errors, miss set work pieces, missing or wrong parts, improper equipment set ups and so forth. A good Poka Yoke must be simple and low maintenance, very reliable, low cost, and designed for the specific workplace condition. When a Poka Yoke detects an error, it should either
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stopping of the line in the middle of a process increases the potential for defects. An effective Poka Yoke must inspect 100 percent of the items and provide immediate feedback for countermeasures (Shingo, 1985).
It was year 1961 when Shigeo Shingo, an industrial engineer at Toyota Motor Corporation introduced the concept of Poka Yoke. Based on Shingo’s long term experience and observation, he developed the concept of Poka Yoke and turned it from the idea into a formidable tool; a tool for achieving zero defect and eventually eliminating the need of quality control inspections. Since then, “Poka Yoke” has been an integral part of Japanese quality and manufacturing systems (Shimbun, 1988).
In its early days, term Poka Yoke was known as baka-yoke, meaning fool proofing. In the operator’s point of view, this term wasn’t very attractive, because of terms have dishonorable and offensive connotation. Soon after the name episode in one of the Japanese car manufacturing plants in 1963, the term to describe this methodology was changed to Poka Yoke. The term “Poka Yoke” stands for mistake proofing; referring originally devices, which serve to prevent the sort of inadvertent mistakes that anyone can make (Manivannan, 2006).
Many definitions for Poka Yoke can be found from the literature. The following statement describes best the idea of Poka Yoke from different aspects:
1. “The original idea behind Poka Yoke is to respect the intelligence of workers. Poka Yoke are for freeing worker’s time and mind to pursue more creative and value adding activities” (Shimbun, 1988).
2. “Error proofing is not so much a lean “tool” as it is a way of thinking and evaluating problems. It is based on a philosophy that people do not intentionally make mistakes or perform the work incorrectly, but for various reason mistakes can and do occur” (Meier, 2006).
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Poka Yokes were originally developed for manufacturing, considered primarily physical devices to prevent mistakes from occurring. Nowadays the whole concept of Poka Yoke has a much more extensive purpose; it can be seen as a tool, as an effective quality control technique and finally as a quality philosophy. The basic principle behind all these "levels" is the prevention of defects. The creator of Poka Yoke concept, Shigeo Shingo, believed that defects could simply be eliminated in the first place, instead of relying on measures taken on after-the-fact. According to Shingo (1986), mistakes that lead to defects can be engineered out of the processes and defects can be eliminated this way. The well-known quality guru, Edward Deming, has once stated that "quality comes not from inspection, but from improvement of the process" (Manivannan, 2006). This statement is also the heart of the Poka Yoke philosophy. Rather than looking for defects, a true goal is to create processes that yield zero defects (Manivannan, 2006).
2.2 Errors and Defects in Poka Yoke
In order to have a thorough understanding of Poka Yoke, an understanding of why mistakes occur and what human factors make mistakes less likely is appropriate (Stewart & Grout, 2001). In addition, discussion of what do the words "mistake", "defect" and "error" mean in the context of Poka Yoke is provided. Shingo has made a clear distinction between a mistake and a defect. Mistakes are inevitable; people are human and cannot be expected to concentrate all the time, or always understand completely the instructions they are given. Defects results from allowing a mistake to reach the customer, and are thus entirely avoidable (Fisher, 1999).
Manivannan (2007) defines that a defect is any deviation from product specifications that may lead to customer dissatisfaction. To be considered defective, the product must deviate from manufacturing or design specifications, and it must not meet the expectations of internal or external customers. According to Shingo (1986) the causes of defects lie in worker errors, and defects are the results of neglecting those errors. It
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eliminated beforehand. On the other hand, from the source inspection’s point of view, Shingo (1986) states that defects arise because errors are made and these two have a cause-and-effect relationship. Errors will not turn into defects if feedback and action takes place at the error stage.
2.2.1 Human Error Classification
Shimbun (1988) classifies ten different kinds of human errors, which are presented in table 2.1. Also Grout (1995) states about mistakes that to error is human. According to these, we will sooner or later come to the conclusion that almost all defects are caused by human errors.
Table 2.1: Classification of Human Errors (Shimbun, 1988).
TYPE OF HUMAN ERROR EXAMPLE
Forgetfulness Sometimes we forget things when we are
not concentrating.
Errors due misunderstanding Sometimes we make mistakes when we jump to the wrong conclusions before we are familiar with the situation
Errors in identification Sometimes we misjudge a situation because we view it too quickly or are too far away to see it clearly
Errors made by amateurs Sometimes we make mistakes through lack of experience.
Willful errors Sometimes errors occur when we decide
that we can ignore rules under certain circumstances.
Inadvertent errors Sometimes we are absentminded and make mistakes without knowing how they are happened.