design for assembly and application using boothroyd...
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DESIGN FOR ASSEMBLY AND APPLICATION USING BOOTHROYD
DEWHURST METHOD
MUHAMMAD SAFUAN BIN OTHMAN
Thesis submitted in fulfillment of the requirements
for the award of the degree of
Bachelor of Mechanical Engineering
Faculty of Mechanical Engineering
UNIVERSITI MALAYSIA PAHANG
APRIL 2010
ii
SUPERVISOR’S DECLARATION
I hereby declare that I have checked this project and in my opinion, this project is
adequate in terms of scope and quality for the award of the degree of Bachelor of
Mechanical Engineering.
Signature
Name of Supervisor: Mr. Mahendran Samykano.
Position: Supervisor
Date: April 2010
iii
STUDENT’S DECLARATION
I hereby declare that the work in this project is my own except for quotations and
summaries which have been duly acknowledged. The project has not been accepted
for any degree and is not concurrently submitted for award of other degree.
Signature
Name: Muhammad Safuan Bin Othman
ID Number: MA06093
Date: April 2010
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ACKNOWLEDGEMENT
This thesis is the end of my long journey in obtaining my Bachelor Degree in
Mechanical Engineering. I have been accompanied and supported by many people in
this journey. It is a pleasant aspect that I have now the opportunity to express my
gratitude for all of them.
First a very special thanks you to my supervisor, Mr. Mahendran for his great
patient and efforts to explain things clearly. He provided encouragements and lots of
good ideas in order for me to complete the testing and thesis writing period. I would
have been lost without his guidance and support.
I would also like to thank all lecturers who had helped me directly or
indirectly and shared their experiences with me. I am also indebted to the support of
my family and friends. They accompanied me went through the toughest moment. A
journey is easier when you travel together. Interdependence is certainly more
valuable than independences.
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ABSTRACT
This paper shows a detailed study to investigate the efficiency of Boothroyd
Dewhurst Design for Assembly (DFA) method that was applied to improve the
product design process. In today competitive world, companies try to cut down the
manufacturing cost and at the same time increase their profit. In order to be a
competent player in the market, the product should arrive into market within a short
time and reasonable price. Assembly cost is one of the major operations in
manufacturing but always ignored during designing stage. In this study, comparative
analysis was done between current and alternative design. The design was done by
using Solidwork software and analyzed by using manual and DFA software analysis
to get the efficiency of current design. Then, by applying Boothroyd Dewhurst DFA
method guideline, alternative design was generated and analyzed using the same
method to compare the effectiveness of this new alternative design. From the study,
it was found that the design efficiency increased from 16.7% to 46.4% when
Boothroyd Dewhurst DFA method was applied. The time of assemble also decreased
from 193.09 seconds to 58.48 seconds per product. From the result, it was proven
that this Boothroyd Dewhurst DFA method was able to improve the design in terms
of design efficiency, product assemble time and labor cost. This method can be
applied in manufacturing company in order to improve their design effectiveness.
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ABSTRAK
Kajian ini menunjukkan tentang kajian lanjut untuk mengkaji kecekapan
kaedah Boothroyd Dewhurst Rekabentuk untuk Pemasangan (DFA) yang
diaplikasikan untuk menambahbaik proses pemasangan rekabentuk. Dalam
persaingan dunia masa kini, syarikat-syarikat berusaha untuk mengurangkan kos
pengeluaran produk dan pada masa yang sama mereka cuba untuk meningkatkan
keuntungan syarikat. Untuk bersaing di pasaran dunia, produk yang dihasilkan
mestilah berada dipasaran di dalam masa yang cepat dengan harga yang berpatutan.
Kos pemasangan adalah salah satu operasi penting dalam bidang pembuatan tetapi
selalu diketepikan semasa proses mereka bentuk. Dalam kajian ini, analisis
perbandingan telah dibuat antara produk semasa dengan produk yang dicadangkan.
Rekabentuk dilakukan dengan menggunakan perisian Solidwork dan dianalisis
dengan menggunakan perkiraan manual dan juga perisian analisis DFA untuk
mendapatkan kecekapan bagi rekabentuk semasa. Kemudian, dengan
mengaplikasikan panduan kaedah Boothroyd Dewhurst DFA, rekabentuk cadangan
dihasilkan dan dianalisis dengan menggunakan kaedah yang sama untuk
membandingkan keberhasilan rekabentuk cadangan ini. Daripada kajian, telah
didapati kecekapan rekabentuk meningkat dari 16.7% kepada 46.4% apabila kaedah
Boothroyd Dewhurst DFA diaplikasikan. Masa untuk pemasangan juga telah
berkurang dari 193.09 saat untuk setiap produk kepada 58.48 saat untuk setiap
produk. Daripada hasil kajian, telah terbukti bahawa kaedah Boothroyd Dewhurst
DFA ini mampu untuk meningkatkan rekabentuk dari segi kecekapan rekabentuk,
masa pemasangan produk dan juga kos tenaga kerja. Kaedah ini boleh diaplikasikan
dalam syarikat pembuatan bagi meningkatkan kerberhasilan rekabentuk.
viii
TABLE OF CONTENTS
Page
SUPERVISOR’S DECLARATION ii
STUDENT’S DECLARATION iii
ACKNOWLEDGEMENTS v
ABSTRACT vi
ABSTRAK vii
TABLE OF CONTENTS viii
LIST OF TABLES xi
LIST OF FIGURES xii
LIST OF SYMBOLS xiv
LIST OF ABBREVIATIONS xv
CHAPTER 1 INTRODUCTION
1.1 Introduction 1
1.2 Objective 2
1.3 Scope of study 2
1.4 Important of study 2
1.5 Problem statement 3
1.6 Summary 3
CHAPTER 2 LITERATURE REVIEW
2.1 Design for assembly 4
2.1.1 Introduction of DFA
2.1.2 Comparison of assembly method
2.13 DFA guidelines
4
7
9
2.2 Boothroyd Dewhurst DFA method 13
2.3 Hitachi Assemblabilty Evaluation method 15
ix
2.3.1 Procedure of AEM 16
2.4 Lucas method evaluation 18
2.5 Summary 20
CHAPTER 3 METHODOLOGY
3.1 Introduction 21
3.2 Overview 21
3.3 Flow chart 22
3.4 Product 24
3.4.1 Product selection
3.4.2 Product information
24
25
3.5 Solid work designing of current product 25
3.6 Boothroyd Dewhurst DFA 29
3.6.1 Manual analysis
3.6.2 Manual handling code
3.6.3 Manual insertion code
3.6.4 Theoretical minimum value
3.6.5 Software analysis
29
30
31
31
31
3.7 Alternative Design 33
3.7.1 DFA guidelines 33
3.8 Solid work designing of alternatives design 34
3.9 Boothroyd Dewhurst DFA analysis for alternative design 35
3.10 Summary 35
CHAPTER 4 RESULTS AND DISCUSSION
4.1 Introduction 36
4.2 Part information 36
4.3 Current design analysis 40
4.3.1 Boothroyd Dewhurst DFA analysis
4.3.2 Manual current design analysis
4.3.3 Selection of part for redesign
4.3.4 Critics of all parts for redesign
41
42
43
45
4.4 Generate alternative design
46
x
4.4.1 Part information
4.4.2 Alternative design analysis
4.4.3 Manual alternative design analysis
47
49
50
4.5 Comparison between current and alternative design 51
4.6 Comparison of part between current and alternative design 53
4.7 Summary 56
CHAPTER 5 CONCLUSION AND RECOMMENDATIONS
5.1 Conclusion 57
5.2 Recommendation 58
REFERENCES
59
APPENDICES
A1 Gantt Chart For FYP1 60
A2 Gantt Chart For FYP2 61
B1 Exploded view of current design 62
B2 Exploded view of alternative design 63
C1 Manual handling table 64
C2 Manual handling table 65
C3 Manual insertion table 66
C4 Manual insertion table 67
D1 Analysis tool of Boothroyd Dewhurst DFA 68
D2 Executive summary of Boothroyd Dewhurst DFA 69
D3 Suggestion for redesign 70
D4 Suggestion for redesign 71
D5 Suggestion for redesign 72
xi
LIST OF TABLES
Table No. Title Page
2.2 Estimated cost for 2 products regarding applying DFMA 5
2.2 Sample Table of Boothroyd Dewhurst manual calculation 14
4.1 Part quantity, theoretical part, and material in the current design 37
4.2 Total number of different parts, total time of assembly, cost and
design efficiency for current design 41
4.3 Design for assembly analysis for current design 42
4.4 Suggestion of reduction for fasteners 43
4.5 Suggestion for redesign 44
4.6 Criticism and suggestion for all part 45
4.7 Part quantity, theoretical part, and material in the alternative
design
47
4.8 Total number of different parts, total time of assembly, cost and
design efficiency for alternative design
49
4.9 Design for assembly analysis for alternative design 50
4.10 Comparison between current and alternative design 51
4.11 Estimation of total product was assembling in one hour for both
designs
52
xii
LIST OF FIGURES
Figure No. Title Page
2.1 Misleading productibility guidelines 5
2.2 DFMA shortens the design process 6
2.3 Effect of DFMA on cost product 7
2.4 Relative costs of different assembly methods by type and
production volume
8
2.5 Production ranges for each type of assembly method 9
2.6 Hook- Under 10
2.7 Snap Fits 11
2.8 Assemblabilty evaluations and design improvement flow diagram 16
2.9 Lucas method procedure assemblies 19
2.10 Architecture of Lucas method system 19
3.1 Schematic flowchart of design for assembly and application using
Boothroyd Dewhurst method.
23
3.2 Car window regulator 24
3.3 Part information flow chart 25
3.4 Base drawing 26
3.5 Extrusion of line 27
3.6 Rail drawing 27
xiii
3.7 Handle drawing 28
3.8 Roller slider drawing 28
3.9 Sliding rail 29
3.10 α and β rotational symmetries 30
3.11 Software analysis 32
3.12 Software analysis 33
4.1 Original design of window regulator structure 38
4.2 Isometric view of current window regulator design 39
4.3 Exploded view of current window regulator design 40
4.4 Exploded view of alternative design 46
4.5 Isometric view of alternative design 46
4.6 Alternative design of window regulator structure 48
4.7 Current design of rail 53
4.8 Alternative design of base 53
4.9 Current design of motor 54
4.10 Alternative design of motor 54
4.11 Current design of roller 55
4.12 Alternative design of roller 55
xiv
LIST OF SYMBOLS
α Rotational symmetry of a part about an axis perpendicular to its axis of
insertion
β Rotational symmetry of a part about its axis of insertion
s Second
mm Millimetre
xv
LIST OF ABBREVIATIONS
DFA Design for assembly
DFMA Design for manufacturing assembly
CAE Computer aided engineering
AEM Assemblability evaluation method
NSF National Science Foundation
CAD Computer aided engineering
RM Ringgit Malaysia
NM Total Theoretical minimum part
CM Total assembly cost
TM Total assembly time
CHAPTER 1
INTRODUCTION
1.1 Introduction
Design for analysis or design for assembly was done in the early 1970. These
designs actually are done in several stages and include several persons. This process starts
from designers who are design the product and follow up by making prototype. After
prototype was been construct then the process is follow up by testing it and wait for the
approval. These designs for analysis not only finish until there but it continues by
manufacturing team by conduct the manufacturing plant. These planes are to make sure the
product have same functionality and produces in large amount of production. This plans is
to change the. This plans included the tools use, using different materials and different
components. Designs for assembly also are the integration of product design and process
planning into one common activity. The goal is to design a product that is easily and
economically manufactured. The importance of designing for manufacturing is underlined
by the fact that about 70% of manufacturing costs of a product are determined by design
decisions, with production decisions responsible for only 20%. These designs for assembly
is important in improving the quality in design, cut of cost of manufacturing of product and
increase efficiency of product produces
For this study, design for assembly is differ into three types which are Hitachi AEM
method, Lucas method, and Boothroyd Dewhurst method. These 3 methods are the most
usable method in any design process. The different of these 3 methods will be discussed
2
further in literature review. The practice of DFA as a distinct feature of designing is a
relatively recent development, but many companies have been essentially doing DFA for a
long time. For example, General Electric published an internal manufacturing producibility
handbook in the 1960's as a set of guidelines and manufacturing data for designers to
follow. These guidelines embedded many of the principles of DFA without ever actually
calling it that or distinguishing it from the rest of the product development process.
It wasn't until the 1970's that papers and books on the topic began to appear. Most
important among these were the publications of G. Boothroyd that promoted the use of
DFA in industry.
1.2 Objective
For this project, the main objectives are:
To study and apply Boothroyd Dewhurst method in design for assembly
Redesign a product using Boothroyd Dewhurst method.
Evaluate the original design efficiency over new design efficiency.
1.3 Scope of study
Study on Design for Analysis together with Boothroyd Dewhurst methodology.
Evaluate a product as a case study, analyze and redesign the product using
Boothroyd Dewhurst method.
Verification and validation on the method use.
1.4 Important of study
This study is important to simplify the product so that the cost of assembly is
reduced. Applying design for analysis also usually to improved quality and reliability, and a
reduction in production equipment and part inventory. These secondary benefits often
outweigh the cost reductions in assembly.
3
1.5 Problem statement
A manufacturing system is composed of a large number of distinct processes which
all influence product cost, product quality and productivity of system. This problem will
cause a company major losses in their business. Other than that, mostly lot of product
nowadays consist a lot of fasteners and unnecessary features. As a result, it will increase the
time to market. By the time reach to market, the design is already outdated and finally it
will lose its competency.
One of the methods used to overcome this problem is by using Boothroyd Dewhurst
DFA method. The advantage of this method is the problem regarding of manufacturing can
be detected in the early stage of design. This method also suggested the best possible way
to assemble a product by eliminating fasteners to other type of assemble such as snap fit,
press fit and etc. Other than that, this method also suggested to combine a part or
eliminated the unnecessary part. By applying this method, time of assemble can be lesser
and more product can be produce. This method also estimated the product cost of assemble
and design efficiency of the product in the early stage of design, designers in manufacturing
system always can estimated their efficiency and labor cost of their design before the
product been produce
This study is aim to improve the design and reduce the assembly parts as well as its
cost. Lesser parts mean lesser time needs to assembly the product as well as the cost.
1.6 Summary
This chapter described about overall introduction of this project. Background of this
project will discuss after defining problem statement. Then, scopes and objectives of this
project are determined as guidelines of the project.
CHAPTER 2
LITERATURE REVIEW
2.1 Design for assembly
2.1.1 Introduction of design for assembly (DFA)
The development of the original design for assembly method is early on 1960s on
automatic handling. A group technology classification system was developing to catalogue
automatic handling solutions for small parts. This shows that classification system could
help the designers to design parts that would be easy to handle. This continue in the mid of
70s when U.S National Science Foundation (NSF) awarded a substantial to extend this
approach to the general areas of design for manufacturing and design for analysis.
University of Salford in England also was awarded a government grant to study product
design for automatic assembly in the middle 70s (G.Boothroyd, at. all., 2002).
Also in the 1960s there was much talk about designing product so they could be
manufactured so easily. Recommendations commonly known as productibility guidelines
were develop. Figure 2.1 shows typical design guidelines that show how to simplifying the
individual parts. But it has made a wrong assumption that single complex parts are less
expensive to manufacture compare to the assembly part. This shows in Table 2.1 how the
author is made a wrong assumption (G. Boothroyd, at. all., 2002). Reflex with the figure
and table on the next page.
5
Figure 2.1: Misleading productibility guidelines (G. Boothroyd, at. all., 2002)
In Table 2.1, it shows that the right design is more expansive compare to the left
design. This shows how the author is made a wrong assumption according to the
implementation of DFA.
Table 2.1: Estimated cost for 2 products regarding applying DFMA
(G. Boothroyd, at. all., 2002)
6
Design also would be detailing of materials, shapes, and tolerances. Therefore, not
only is it important to take manufacture and assembly into account during product design,
but also these considerations must occur early as possible in the design cycle. This is
illustrated qualitatively in Figure 2.2 which is showing that extra time spent early in the
design process is more than compensated for by savings in time when prototypes takes
places. Thus, in addition to reducing product cost the application of design for assembly
shortens the times to bring product to the markets (G. Boothroyd, at. all., 2002).
Figure 2.2: DFMA shortens the design process
(G. Boothroyd, at. all., 2002)
7
Other than that, Figure 2.3 also shows effect of design for assembly on cost product.
Figure 2.3: Effect of DFMA on cost product
(Boothroyd at. all., 2002)
2.1.2 Comparison of Assembly Methods
Assembly methods can be divided into three major groups. In manual assembly,
parts are transferred to workbenches where workers manually assemble the product or
components of a product. Hand tools are generally used to aid the workers. Although this is
the most flexible and adaptable of assembly methods, there is usually an upper limit to the
production volume, and labor costs. Fixed or hard automation is characterized by custom-
built machinery that assembles one and only one specific product. Obviously, this type of
machinery requires a large capital investment. As production volume increases, the fraction
of the capital investment compared to the total manufacturing cost decreases. Indexing
tables, parts feeders, and automatic controls typify this inherently rigid assembly method.
Sometimes, this kind of assembly is called "Detroit-type" assembly. Soft automation or
robotic assembly incorporates the use of robotic assembly systems. This can take the form
of a single robot, or a multi-station robotic assembly cell with all activities simultaneously
controlled and coordinated by a PLC or computer (Vincent Chan, at. all., 2003). Although
8
this type of assembly method can also have large capital costs, its flexibility often helps
offset the expense across many different products. Graphically, the cost of different
assembly methods can be displayed as in Figure 2.4 show the non-linear cost for robotic
assembly reflects the non-linear costs of robots. The appropriate ranges for each type of
assembly method are shown approximately in Figure 2.5. Assembly methods should be
chosen to prevent bottlenecks in the process, as well as lower costs.
Figure 2.4: Relative costs of different assembly methods by type and production volume.
(Vincent Chan, at. all., 2003)
9
Figure 2.5: Production ranges for each type of assembly method
(Vincent Chan, at. all., 2003)
2.1.3 DFA Guidelines
Differrent books described DFA Guidelines in different ways. Some authors list
many guidelines and described it with detail while other authors categorised it with few list
before divided the main principle to another few principle. But surely the main objectives
for all guidelines remain same, to reduce the cost of assembly. The principles of DFA are:
1. Reduce the parts count. The objectives of this guidelines is to minimize the total
number of parts. There is two ways how this objectives can be achieved: First, design for
minimum number of parts and second, minimize number of fasteners and their components.
2. Design for minimun number of parts. Focussing on the main parts, when number of
parts is decreasing, the cost the assembly and whole product will also decreasing. There is 3
factors that should be considered. First, reduce the number of parts, second, remove non
10
essential components with its functions still achieved and third, combine several parts into
one components and manufactures as an integral multifunctional component.
3. Minimize number of fasteners and their components. Screw and washers can
increase the cost and time to assembly. Other alternatives fasteners can be used to replace
the screw and washers, such as snap fits, press fits and molded hinges, straps or hook. It
seems obvious with this technique (reduce parts count), the assembly costs would be less,
but the question remains whether the overall manufacturing costs have been reduced. Next
guidelines will show how to reduce overall cost (Poli, 2001).
Figure 2.6 show example of product with hook-under. This design is use as a
replacement of screw without sacrifice the function.
Figure 2.6: Hook- Under (Poli, 2001)