ASSEMBLABILITY DESIGN EFFICIENCY (ADE) ANALYSES FOR
DESIGN FOR AUTOMATIC ASSEMBLIES
BAIZURA BINTI ZUBIR @ ZUBAIR
A dissertation submitted in partial fulfilment of the
requirements for the award of the degree of
Master of Engineering –Advanced Manufacturing Technology
FACULTY OF MECHANICAL ENGINEERING
UNIVERSITI TEKNOLOGI MALAYSIA
NOVEMBER 2007
iii
To my beloved husband and daughter, thank you for your patients and loved
To my beloved father, thank you being a good father
To my mother, I will always miss you
iv
ACKNOWLEDGEMENT
During the process in finishing this dissertation, I had face many problems
which sometimes make me want to give up. Thankfully, I have the best and dedicated
supervisor, Dr Ariffin haji Abdul Razak. He gave the encouragement,guidance, and
critics to help me to finish this dissertation. Without his continued support and interest,
this dissertation would not have been the same as presented here.
My sincere appreciation also extends to others who have provided assistance at
various occasions. Their views and tips are useful indeed. I am also very grateful to have
a supportive and wonderful husband that had been so patient and always be at my back
for all the time. Thank you ALL so much.
v
ABSTRACT
The ability to quickly develop new products, which are of the lowest cost, the
highest quality and the fewest environment impact, is a key factor to meet the global
market demand. Design for Assembly (DfA) has been most widely applied in industries
with most impressive achievements. Since the prevalence of three well known DfA tools
– Boothroyd-Dewhurst DfA methodology, Hitachi Assemblability Evaluation Method
(AEM) and Lucas-Hull DfA method – in industries, significant developments have been
attempted in several directions not only by manual assembly but also by automatic
assembly. The purpose of this project is to determine the Assemblability Design
Efficiencies (ADE) by implementing the assembly analyses on the selected mechanical
product for Design for Automatic Assemblies (DFAA) methodology. The results from
the analyses will be used for further design improvements.
vi
ABSTRAK
Keupayaan untuk menghasilkan produk baru yang mempunyai ciri-ciri seperti
mempunyai kos yang rendah, tinggi kualiti dan dapat menghasilkan impak yang
minimum pada persekitaran merupakan faktor utama di dalam memenuhi pasaran
antarabangsa. Pemasangan untuk Reka bentuk (DfA) telah banyak diaplikasikan di
dalam industri dan telah menghasilkan pelbagai kejayaan. Sejak kewujudan tiga alat
DfA yang ternama – kaedah Boothroyd-Dewhurst DfA, kaedah analisis Hitachi
Assemblability (AEM) and kaedah DfA Lucas-Hull– di dalam industri, banyak
pembangunan penting telah dijalankan samada secara pemasangan insani ataupun
pemasangan automatik. Tujuan projek ini dijalankan ialah untuk menentukan
Kecekapan Keupayaan Pemasangan (ADE) dengan mengimplikasikan analisis
pemasangan pada produk mekanikal yang terpilih untuk Kaedah Pemasangan Automatik
bagi Reka bentuk (DFAA). Keputusan daripada analisis ini akan digunakan untuk
penambaikan reka bentuk akan datang.
vii
TABLE OF CONTENTS
CHAPTER
1
TITLE
PAGE
DECLARATION
ii
DEDICATION
iii
ACKNOLEDGEMENTS
iv
ABSTRACT
v
ABSTRAK
vi
TABLE OF CONTENTS
vii
LIST OF TABLES
xiv
LIST OF FIGURES
xvi
LIST OF SYMBOLS
xviii
LIST OF APPENDICES
xix
INTRODUCTION
1
1.1
Problem Statement
1
1.2
Objective of Study
3
1.3
Scope of Study
4
1.4
Methodology of Study
4
1.5
Significance of Findings
7
1.6
Report Structure
8
1.7
Summary
9
viii
2
LITERATURE REVIEW ON DESIGN FOR MANUAL
10
ASSEMBLY METHODOLOGY
2.1
Introduction
10
2.2
Design for “X”
11
2.3
Approaches for Implementing DFA
13
2.3.1 Hitachi Assemblability Evaluation Method
13
(AEM).
2.4
2.3.2 Boothroyd-Dewhurst (B-D) DFA
14
2.3.3 Lucas DFA
15
Assemblability Measures
2.4.1 Hitachi Assemblability Evaluation Method
17
17
(AEM)
2.5
2.4.2 Boothroyd Dewhurst DfA
18
2.4.3 Lucas DFA
20
Examples of DFA Methodologies
2.5.1
Redesign of a simple product using Hitachi
22
22
Assemblability Evaluation Method (AEM).
2.5.2
Redesign of a simple product using the
25
Boothroyd-Dewhurst DFA method
2.5.3 Redesign of a drain pump assembly using
29
Lucas DFA
2.6
3
Summary
DESIGN FOR AUTOMATIC ASSEMBLY (DFAA)
32
33
METHODOLOGY
3.1
Introduction
33
3.1.1
Fixed/ Hard automation
34
3.1.1
Robotic Assembly/ Soft automation
35
ix
3.2
Structure of DFAA
3.2.1
3.2.2
38
Product Level
38
3.2.1.1
Reduce Number of Parts
39
3.2.1.2
Unique Parts
40
3.2.1.3
Base object
41
3.2.1.4
Design base object
41
3.2.1.5
Assembly directions
42
3.2.1.6
Parallel operations
43
3.2.1.7
Chain of tolerances
44
3.2.1.8
Disassembly
44
3.2.1.9
Packaging
45
Part Level
45
3.2.2.1
Need to Assemble Part?
47
3.2.2.2
Level of Defects
48
3.2.2.3
Orientation
48
3.2.2.4
Non-Fragile parts
49
3.2.2.5
Hooking
50
3.2.2.6
Centre of Gravity
50
3.2.2.7
Shape
51
3.2.2.8
Weight
52
3.2.2.9
Length
52
3.2.2.10 Gripping
54
3.2.2.11 Assembly Motion
54
3.2.2.12 Reachability
55
3.2.2.13 Insertion
56
3.2.2.14 Tolerances
56
3.2.2.15 Holding Assembled Parts
57
3.2.2.16 Fastening Method
58
3.2.2.17 Joining
58
3.2.2.18 Check/Adjust
59
x
3.3
Applications of DFAA
3.3.1
Design and Evaluation During Early
59
59
Product Development
3.3.2
Redesign and Evaluation of an Existing
60
Product
4
3.4
Evaluation Philosophy and Criterions of DFAA
61
3.5
Summary
62
PRODUCT DETAIL FOR OLD DESIGN
63
4.1
Introduction
63
4.2
Product Specification
64
4.3
Product Structure
66
4.3
Product Assembly Operation Sequences
67
4.4
5
4.3.1
Base Part
67
4.3.2
Cover Part
69
Summary
72
EVALUATION OF THE ORIGINAL DESIGN
73
5.1
Introduction
73
5.2
Product Level Evaluation of The Old Design
74
5.2.1
Reduce Number of Parts
74
5.2.2
Unique Parts
75
5.2.3
Base Object
75
5.2.4
Design Base Objects
75
5.2.5
Assembly Directions
76
5.2.6
Parallel Operations
76
5.2.7
Chain of Tolerances
78
5.3
Part Level Evaluation of The Old Design
78
8.2.1
79
Base Socket
xi
5.2
6
8.2.2
Switch On/Off
80
8.2.3
Spring
80
8.2.4
Panel 3 Pin
80
8.2.5
Cover Socket
80
8.2.6
Life Plate
81
8.2.7
Life Clamp
81
8.2.8
Life Screw φ6 X 11
81
8.2.9
Life U Plate
81
8.2.10 Connector Panel 3 Pin
82
8.2.11 Plate Switch On/Off
82
8.2.12 Earth U Plate
82
8.2.13 Earth Plate
82
8.2.14 Earth Clamp
83
8.2.15 Earth Screw φ6 X 11
83
8.2.16 Neutral U Plate
83
8.2.17 Neutral Clamp
83
8.2.18 Neutral Screw φ6 X 11
84
8.2.19 Screw φ5 X 12
84
8.2.20 Screw φ6.5 X 23
84
Summary
PROPOSED IMPROVEMENTS ON THE ORIGINAL
84
86
DESIGN
6.1
Introduction
86
6.2
Improvement of The Original Design
86
6.2.1
Eliminating Screws φ5 X 12 and Changing
87
to Snap Fits
6.2.2
Joining Life Plate, Life U Plate, Panel 3 Pin
88
and Connector 3 Pin
6.2.3
Joining Earth Plate, and U Plate
89
xii
6.2.4
6.3
7
Summary
PRODUCT DETAIL FOR PROPOSED DESIGN
90
91
92
7.1
Introduction
92
7.2
Product Specification
92
7.3
Product Structure
94
7.4
Product Assembly Operation Sequences
94
7.5
8
Joining Clamp and Screw φ6 X 11
7.4.1
Base Part
95
7.4.2
Cover Part
95
7.4.3
All Parts
96
Summary
EVALUATION OF THE NEW DESIGN
97
98
8.1
Introduction
98
8.2
Product Level Evaluation of The New Design
98
8.3
8.2.1
Reduce Number of Parts
99
8.2.2
Unique Parts
99
8.2.3
Base Object
100
8.2.4
Design Base Objects
100
8.2.5
Assembly Directions
100
8.2.6
Parallel Operations
100
8.2.7
Chain of Tolerances
101
Product Level Evaluation of The New Design
102
8.3.1
Base Socket
103
8.3.2
Switch on/off
103
8.3.3
Spring
103
8.3.4
Panel 3 Pin
103
8.3.5
Cover Socket 3 Pin
104
xiii
8.4
9
8.3.6
Life Plate
104
8.3.7
Life Clip
104
8.3.8
Earth Plate
104
8.3.9
Earth Clip
105
8.3.10 Neutral Plate
105
8.3.11 Neutral Clip
105
8.3.12 Screw φ6.5 X 23
105
Summary
106
DISCUSSION
107
9.1
Introduction
107
9.2
Comparison Between The Original Design and
108
Proposed Design
10
9.2.1
Number of Components
110
9.2.2
Number of Unique Components
111
9.2.3
Assembly Index for Product Level
112
9.2.4
Assembly Index for Part Level
112
CONCLUSIONS AND FUTURE
113
RECOMMENDATIONS
10.1 Introduction
113
10.2 Conclusions
113
10.3 Future Recommendations
115
REFERENCES
116
APPENDICES
118
xiv
LIST OF TABLES
TABLE NO.
TITLE
PAGE
1.1
Gantt chart for Master Project I
5
1.2
Gantt chart for Master Project II
7
2.1
DFX as lifecycle oriented or ability oriented (WDK, 1993)
12
2.2
DFA worksheet analysis
18
2.3
Evaluation score and the cost ratio of the original design
23
2.4
Evaluation score and the cost ratio of redesign 1
24
2.5
Evaluation score and the cost ratio of redesign 2
25
2.6
Manual assembly worksheet for the original design
26
2.7
Manual assembly worksheet for Redesign 1
27
2.8
Manual Assembly Worksheet for Redesign 2
28
3.1
The evaluation of the part reduced in the product
40
3.2
The evaluation of the unique parts in the product
40
3.3
The evaluation of the base object of the product
41
3.4
The evaluation of the design base object of the product
42
3.5
The evaluation of the assembly directions of the product
42
3.6
The evaluation of the parallel operations of the product
43
3.7
The evaluation of the chain of tolerances of the product
44
3.8
The evaluation need to assemble part of each part
45
3.9
The evaluation level of defects of each part
47
3.10
The evaluation for orientation of each part
48
3.11
The evaluation for non-fragile parts
48
3.12
The evaluation for hooking of each part
49
3.13
The evaluation for centre of gravity of each part
49
3.14
The evaluation for shape of each part
50
3.15
The evaluation for weight of each part
51
xv
3.16
The evaluation for length of each part
52
3.17
The evaluation for gripping of each part
52
3.18
The evaluation for assembly motion of each part
53
3.19
The evaluation for reachability of each part
54
3.20
The evaluation for insertion of each part
55
3.21
The evaluation for tolerances of each part
55
3.22
The evaluation for holding assembled parts
56
3.23
The evaluation for fastening method of each part
57
3.24
The evaluation for joining of each part
58
3.25
The evaluation for check/ adjusts of each part
59
3.26
Evaluation sheet for Product Level
61
3.27
Evaluation sheet for Part Level
62
4.1
Three (3) Pin Wall Socket Specification
64
5.1
Evaluation sheet of product level for the old design of 3 pin
74
wall socket
5.2
Evaluation sheet of part level for the old design of 3 pin wall
79
socket
7.1
Specification of Three (3) Pin Wall Socket New Design
92
8.1
Evaluation sheet of product level for the old design of 3 pin
99
wall socket
8.2
Evaluation sheet of part level for the new design of 3 pin
102
wall socket
9.1
Comparison in Percentage between the Original Design and
108
Proposed Design
9.2
Comparison between the Number of Components in Original
Design and New Design
111
xvi
LIST OF FIGURES
FIGURE NO.
TITLE
PAGE
1.1
Types of DFA
2
1.2
Flow Chart Master Project I
5
1.3
Flow Chart Master Project II
6
2.1
Assembly sequence flow chart
21
2.2
Original design
22
2.3
Redesign 1
23
2.4
Redesign 2
24
2.5
Original design
25
2.6
Redesign 1
27
2.7
Redesign 2
28
2.8
Original drain pump assembly design
30
2.9
Redesign using the Lucas DFA method
31
3.1
Classification of Automatic Assembly
33
3.2
DFAA Method
38
3.3
Suggested structure for Product level in the DFAA method
39
(Stephan Eskilander, 2001)
3.4
Suggested structure for Part level in the DFAA method
46
(Stephan Eskilander, 2001)
4.1
(a) Front view (b) Back view of 3 pin wall socket
63
4.2
Three (3) Pin Wall Socket Structure of the Old Design
66
4.3
Summary of the Assembly Process for Base Part
67
4.4
(a) Before assembled (b) After assembled for base part
68
4.5
Assembly Sequences for Cover Part
70
4.6
(a) Before assembled (b) After assembled for cover part
71
5.1
Parallel Operations
77
xvii
6.1
The location of screw φ5 X 12 on the 3 pin wall socket
86
6.2
The Proposed Design from Screws φ5 X 12 to Snap Fits
87
6.3
The Proposed Design from Separate Life Plates to a Life
88
Plate
6.4
The Proposed Design from Separate Earth Plates to an Earth
89
Plate
6.5
The Proposed Design from Separate Clamp and Screw
89
φ6 X 11 to a Clip
7.1
Three (3) Pin Wall Socket Structure of the New Design
93
7.2
Summary of the Assembly Process for Base Part
94
7.3
Assembly Sequences for Cover Part
95
7.4
Assembly Sequences for 3 Pin Wall Socket of the New
96
Design
8.1
Parallel Operations
101
9.1
Comparison Number of Components in Old and New
109
Designs
9.2
Comparison Number of Unique Components in Old and
109
New Designs
9.3
Comparison between Assembly Index in Old and New
Designs
110
xvi
LIST OF SYMBOLS
AEM - Assemblability Evaluation Method
E
- Assemblability Evaluation Score
DFA
- Design for Assembly
DFAA - Design for Automatic Assembly
DFM - Design for Manufacture
DFE
- Design for environment
DFC
- Design for cost
DFT
- Design for test
DFMA - Design for Manufacture and Assembly
DFX
- Design for “X”
TM
- Assembly time
CM
- Assembly cost
NM
- Theoretical minimum number of parts
ADE - Assembly Design Efficiency
K
- Estimated Assembly Cost Ratio
xix
LIST OF APPENDICES
APPENDIX
TITLE
PAGE
A1
Manual Handling Time (seconds)
118
A2
Manual Insertion and Fastening Time (seconds)
119
B1
Design Samples of 3 Pin Wall Socket (Overall)
120
CHAPTER 1
INTRODUCTION
1.1
Problem Statement
Design for assembly (DFA) is a way to improve assembly ease and reduce
assembly time. It will also reduce product costs by reducing the number of parts,
optimizing manufacturing processes, simplifying parts handling and improving product
assembly. Furthermore, the implementation of DFA will encourage the design of
products to be produced at minimum cost with maximum quality and reliability. Many
leading companies such as Ford, Kodak, General Motors, IBM, NCR, Xerox and more
have save millions of money when using DFA analysis in their designs.
DFA indicates the important in analyzing both the part design and the whole
product for any assembly problems early in the design process. Furthermore, it can also
be defined as "a process for improving product design for easy and low-cost assembly,
focusing on functionality and on assemblability concurrently."
DFA is classified into two major groups: manual and automatic assembly as
shown in Figure 1.1.
2
Design for Assembly
(DfA)
Design for Manual
Assembly
Design for Automatic
Assembly
Figure 1.1: Types of DFA
Design for manual assembly involves benches or simple conveyors and the
assembly station has bins with un-oriented parts. Besides that, it also has simple jigs and
fixtures with manual clamping and simple, light tools with an inexpensive setup costs.
On the other hand, design for automatic assembly (DFAA), involves any
mechanical assembly process which perform assembly operations without human
interaction. DFAA is divided into two: high speed (special purpose) transfer assembly
and robotic assembly. High speed transfer assembly involved machines that are built to
produce specific product. The components are part feeders, single purpose workheads
and transfer devices. Meanwhile, the robotic assembly is similar to non-synchronous
special purpose assembly stations, except the robots replace the single-purpose
workheads.
Between these two types of DFA, the most common practice is manual assembly
due to its versatility, flexibility, economical and sensing capabilities of human assembly
workers. Meanwhile, for automatic assemblies the characteristics above are difficult to
get economically but the advantage is mechanical assembly equipments have the
capability to work many hours compare to human assembly workers.
However, when we apply automatic assembly on the product it can also be
implemented on manual assembly. Mazka (1985) stated that “Any product designed for
automated assembly will be easier to assemble manually”. It means that, if a product
can be prepared for automatic assembly, it will also be much easier for a human to
assemble. According to Herbertsson (1999) in 1960s, when products began to be
3
redesigned for automatic assembly, it was often discovered that the redesigned product
was so easy to assemble manually that automatic assembly was no longer economically
feasible.
Due to potential benefits that DFAA have compare to DFA for manual assembly
so for this project, we will focus on DFAA to improve the product design of a
mechanical product. At the same time, we also have to consider some operations that
may be have to be carried out manually, which it is necessary to include also the
analysis for manual assembly.
Besides that, in DFA analysis we can compare the assembly efficiency for both
DFA for manual assembly and DFAA for automatic assembly. From there, we can make
improvements on the product itself that will suit automatic assembly process that in
return will give benefits to us.
The product case study of a 3 pin wall socket will clarify the application of
DFAA analysis, show the utility of the product structure of DFAA method, and allow
the exploration between product evolution of the original design and proposed design
for further improvements.
1.2
Objective of Study
The objective of the study is to improve the product design by determining the
Assemblability Design Efficiencies (ADE) using Design for Automatic Assemblies
(DFAA) methodology for mechanical product.
4
1.3
Scope of Study
The scope of this study is to use Design for Automatic Assembly (DFAA)
methodology in assembly analyses. A case study of a mechanical product will clarify
the application of the method with the analyses and percentage of ADE.
1.4
Methodology of Study
The methodology of the study for Master Project I and II were included in
session 2006/2007 semester II and session 2007/2008 semester I. The details of this
methodology are shown in forms of flow diagrams (Figure 1.1 and 1.2) and Gantt
charts (Table 1.1 and 1.2) which are located by semesters.
For Master Project I, the project was done in semester 2006/2007 (II). The flows
of works are shown in Figure 1.2 and Table 1.1.
5
Start
Idea Generation
Gantt Chart & Flow Chart
Definition Problems
Semester
2
Data
Collection
Presentation
Brainstorming
Primary Report
Literature Review
No
DFAA Evaluation Original Design
OK
Figure 1.2: Flow Chart Master Project I
No.
1
2
3
4
5
6
7
8
Dec
26
Task Descriptions
1
January
8 15 22
29
2006/2007 (II)
February
5 12 19
Problem Definition
Data Collection
Literature Review
Product Description
DFAA Evaluation of the Original Design
Propose Design Improvement
Primary Report
Presentation
Table 1.1: Gantt chart for Master Project I
26
5
March
12 19
26
April
2
6
For Master Project II, the project was done in semester 2006/2007 (III). The
flows of works are shown in Figure 1.3 and Table 1.2.
Semester
2
DFAA Evaluation New Design
OK
No
Yes
Comparison of the Results
Discussion of the Results
Conclusion
Final Report
End
Figure 1.3: Flow Chart Master Project II
7
No
Task Descriptions
1
2
3
4
5
6
7
Continue Proposing Design Improvements
DFAA Evaluation of the New Design
Comparison of the results
Discussion of Results
Conclusion
Final Report
Presentation
2007/2008 (I)
July
August
September
9 16 23 30 6 13 20 27 3 10 17 24 1
October
November
8 15 22 29 5 12 19
Table 1.2: Gantt chart for Master Project II
1.5
Significance of Findings
DFAA is a way to reduce the part count in a design. The way it is done is by
using a good design practice rules and guidelines on how the product can be assembled
in most efficiently and economically ways. As a result from the approach, it will
reduced the product cost, time-to-market and improve product quality.
The analysis of DFAA methodology in this project using ADE on the original
and proposed design will improve the product design of this case study. This analysis is
evaluative methods that rate or score the assemblability of designs at an early stage in
the design process. They use their own synthetic data to provide guidelines and metrics
to improve the design in its ability to be assembled. From the result, it can improve the
product design for further improvement in future.
8
1.6
Report Structure
The report of this project is divided into ten (10) chapters which comprises
the ADE analyses for DFAA. Consequently, towards developing a better understanding,
all the contents were developed in order to meet the knowledge and application of
DFAA.
Chapter 1 explores the introduction to the problem which consists the reality of
the usage and benefits of DFAA in today’s industries. Then, the objective of the project
is highlighted together with the scope of the project. Later, the project methodology is
shown in Gantt chart and flow chart. Afterwards, the significance of the findings was
discussed to give a better view on the impact of the project. Lastly, the report structure
is to summarize the contents of the project.
Chapter 2 is on the literature review on design for manual assembly
methodology. In this chapter, design for “X” is included to brief the function of “X” as a
specific property or a lifecycle phase of the product. Then, the tools use in implementing
DFA is then discussed along with the assemblability measures. The tools discussed here
were Boothroyd Dewhusrt method, Hitachi Assemblability Evaluation method and
Lucas DFA evaluation method. Later, the examples of DFA methodologies were given
to provide better understanding on DFA.
Chapter 3 explains on Design for Automatic Assembly (DFAA). It shows the
structure and applications of DFAA in industries. Besides that, it also explains on
evaluation philosophy along with the design rules and evaluation criterions.
Chapter 4 discusses on the old design of the product where it explained the
product specification, material and structure. Then, it describes the function of each
component and continued with the product assembly operation sequences. Then, the
9
weakness of the original design is discussed to make better improvements on the
proposed design
Chapter 5 is regarding the evaluation of the original design which is done at
product level and part level evaluation.
Chapter 6 illustrates the ideas and sketches of the proposed design. It also
includes the minor and major improvements on the original design.
Chapter 7 discusses on the proposed design of the product where it explaines the
product specification, material and structure. Then, it describes the function of each
component and continues with the product assembly operation sequences.
Chapter 8 is regarding the evaluation of the proposed design which is done at
product level and part level evaluation.
Chapter 9 consists of the discussion of the whole project regarding the
comparison between the old design and proposed design of the wall socket.
Chapter 10 is the final chapter which is the conclusion of the project and the
suggestions for future recommendation of the project.
1.7
Summary
This project concentrated on the improvement of the product design by using
Design for Automatic Assemblies (DFAA) methodology. It is done by determining the
Assemblability Design Efficiencies (ADE) for a mechanical product.
CHAPTER 2
LITERATURE REVIEW ON DESIGN FOR MANUAL ASSEMBLY
METHODOLOGY
2.6
Introduction
Design for manual assembly consists of parts that are conveying to workbenches
where workers manually assemble the product or components of a product. Hand tools
are generally used to assist the workers. Although this is the most flexible and adaptable
of assembly methods, there is usually an upper limit to the production volume, and
labour costs (including benefits, cases of workers compensation due to injury, overhead
for maintaining a clean, healthy environment, etc.) are higher.
Obviously, the following design guidelines for manual assembly depend on the
skill of the worker which consists of:
ƒ
eliminate the need for workers to make decisions or adjustments.
ƒ
ensure accessibility and visibility.
ƒ
eliminate the need for assembly tools and gauges (i.e. prefer self-locating parts).
ƒ
minimise the number of different parts - use "standard" parts.
ƒ
minimise the number of parts.
ƒ
avoid or minimise part orientation during assembly (i.e. prefer symmetrical
parts).
ƒ
prefer easily handled parts that do not tangle or nest within one another.
11
Many of the products do not lend themselves to these guidelines. Many such
products are sold as "ready-to-assemble" kits or require that assembly be shifted to
cheaper labour markets.
2.7
Design for “X”
Several companies try to reduce product cost and time-to-market besides
improving their product quality. That is why product designers are required in a
company. They are required to give advice consists of good design practice rules and
guidelines on how the product can most be most efficiently and economically
assembled. All this is requirements applies on DFA.
The applications of DFA are formally known and used in various companies in
different regions in the world. It gave improvements on the product design based on the
assembly ease. Later on, it is extended to other aspects of designs that reflected
concurrent engineering which include design for manufacture (DFM), design for
environment (DFE), design for cost (DFC), design for test (DFT), design for fabrication
(DFF) and etc. Generally, all this application can be referred as design for “X” or DFX.
DFX is the aim activity to fit the life phase system. According to WDK
(1993), there are two ways to explain X which X can be:
1-
A specific property (for example quality, cost or environmental effects).
2-
A lifecycle phase of the product (for example part assembly, manufacturing or
service) or one of the sub processes (for example feeding or gripping).
WDK also explained that there are different aspects of X which can be seen
12
in Table 2.1.
Environment
Risk
Flexibility
Efficiency
Cost
Time
Quality
Table 2.1: DFX as lifecycle oriented or ability oriented (WDK, 1993)
Planning
Fabrication
Assembly
Design for
Assembly
Testing
Transport
Sales
Installation
Operation
Service
Scrapping
Design for
Flexibility
Recycling
Deposition
The common DFX methods that are most being used are Design for Assembly
(DFA) and Design for Manufacture (DFM). Other methods are rare being used because
there are rather new and have not commonly used yet.
DFX tool is used by multifunctional teams in a company to attract and direct the
information from various departments to the designer. This information must be in a
common language so it is easier for everyone to understand.
13
2.8
Approaches for Implementing DFA
DFA are measured by three of the better-known quantitative evaluation
techniques: Boothroyd-Dewhurst (USA), Lucas (UK) and Hitachi (Japan). All of these
three evaluations have been used in industry. The first evaluation method was Hitachi
Assemblability Evaluation Method (AEM) where it was first developed in the late
1970s. Later, Design for Assembly (DFA) was being introduced around 1980 to reflect
the work of Professor Geoffrey Boothroyd at the University of Massachusetts. The
Lucas DFA method was developed in the early 1980's by the Lucas Corp. Among these
three methods, Boothroyd-Dewhurst is the most widely used.
2.8.1
Hitachi Assemblability Evaluation Method (AEM).
The Hitachi AEM analyses the motions and operations, called 'assembly
operations', necessary to insert and secure each component of the product. A simple
downward motion is considered to be the easiest and fastest assembly operation. Penalty
points are awarded for every motion or operation that differs from, or is in addition to,
this simple motion. This method makes use of assemblability and assembly cost ratio
indices to identify the weak points of a design.
The procedure begins by entering the motions and operations necessary for
assembly onto an AEM form. From drawings (detailed or conceptual) or samples, the
analyst completes an AEM form by entering the part names and numbers in the same
order that assembly takes place The form is used to compare the assembly processes to
the optimum, and given a penalty from the synthetic assembly data.
14
The AEM does not distinguish between manual, robotic and automatic assembly.
Two reasons for this are given: The strong correlation between the degree of assembly
difficulty involved in manual, robot and dedicated assembly, and the difficulty involved
in predicting the production mode at the design stage.
Hitachi claims that the system is simple and easy to use, and that that it saves
them tens of millions of dollars annually. Its application is mandatory within the
company (Andreasen et al. 1988).
2.8.2
Boothroyd-Dewhurst (B-D) DFA
B-D DFA evaluation centres on establishing the cost of handling and inserting
component parts. This procedure is mainly aimed at mechanical assemblies. The process
can be applied to manual or automated assembly, which is further subdivided into high
speed dedicated or robotic. An aid to the selection of the assembly system is also
provided by a simple analysis of the expected production volume, pay back period
required, number of parts in the assembly, and number of product styles. Regardless of
the assembly system parts of the assembly are evaluated in terms of, ease of handling,
ease of insertion and a decision as to the necessity of the part in question. The findings
are then compared to synthetic data and from this a time and cost is generated for the
assembly of that part.
The design for assembly work has aroused interest in the USA, and several large
companies like Ford, Xerox, General Electric, and General Motors have tested the
system. The system has also been examined by several large companies in Europe
(Andreasen et al. 1988).
15
2.8.3
Lucas DFA
The Lucas procedure aroused from the idea that a knowledge-based approach,
used in conjunction with a CAD system, was a possible way forward. The structure and
expertise used in this system are the result of knowledge engineering in organizations
which are involved in the manufacture and marketing of mechanized (flexible and
dedicated) assembly systems. This technique shares with the Boothroyd Dewhurst
procedure the aim of reducing component numbers, and analysis of insertion processes.
There is only a single analysis used for robotic and automatic assembly, and it is
strongly argued that, like AEM, it is equally valuable in manual assembly stations.
While not strictly generative, through questioning the designer about component
functions and end their relationship with the product specification, the procedure can be
used to avoid crucial errors and to provide a better starting point for the design for
assembly processes. Another feature of this technique is an initial specification for the
design of the product assembly system.
The Lucas analysis is carried out using an iterative process of the following
points (in presented order):
ƒ
Product specification
ƒ
Product design
ƒ
Functional analysis
ƒ
Feeding analysis
ƒ
Gripping analysis
ƒ
Insertion analysis
ƒ
Assessment
During product design it is important to decide if each product is unique. If not
standardization of components and assembly procedures should be considered (creating
a product family).
16
Functional analysis is carried out according to the rules of value analysis, and
components are divided in to those which have high functional priority and those
components which are of low functional importance. Assembly cost may be reduced by
elimination or combination of components with low functional importance.
The feeding analysis is concerned with the problems of handling components
and sub-assemblies from the point of manufacture to their presentation with in the
automatic assembly machine. Each component is assigned a feeding cost index.
The gripping analysis examines the ease with which each part can be held for
transportation. Each component is assigned an appropriate index according to its
suitability for griping.
The insertion process analysis requires the designer to generate an assembly
sequence flowchart and to assign and to assign a cost index to the individual process.
The assessment stage involves the systematic completion of the drawing-block for an
assembly, and the result of the analysis are used as an aid to generate improved
proposals which are likewise assessed.
Variables representing the value off each cost index for the entire product are
created: Np (number of parts), Ci (insertion cost), Cp (feeding cost), Cg (gripping cost),
and Cm (labor cost) are minimized, and Nt and Na (totally and annually respectively)
are maximized. Finally, the total cost of assembly is determined.
17
2.9
Assemblability Measures
DFA is a formal analysis procedure that validates and evaluates a product design
with respect to manufacture and assembly of its components parts. It is important to
measure the improvements and goals of DFA. Three methods for DFA measurements
that are considered here: AEM, B-D DFA and Lucas DFA.
2.9.1
Hitachi Assemblability Evaluation Method (AEM)
The Hitachi method offers a number of metrics as its evaluation: assembly time
(AT), assemblability evaluation score (E) which is a scale of 0 (infinitely hard to
assemble) to 100 (ideal assembly), assembly cost ratio (K) that indicates the cost of a
redesign as a ratio of the original cost, and simplicity factor (SF) which is a combination
of E and a measure of the design efficiency of an assembly. This step is followed by the
so called judgement stage, where the evaluation indices are compared with target values.
Finally come design improvement, if necessary.
18
2.9.2
Boothroyd Dewhurst DfA
A DFA analysis is performed by completing a worksheet as shown in Table 2.2
below:
Table 2.2: DFA worksheet analysis
c9
Name of assembly
minimum parts
c8
Estimation for theoretical
Operation time = c2(c4 + c6)
c7
Operation cost = 1.069 x 10-3(c7)
c6
Manual insertion time per code
c5
Manual insertion code
c4
Manual handling time per part
c3
Manual handling code
carried out consecutively
c2
No of times the operation is
Part ID
β
α
c1
WALL
SOCKET
Σ
TM
CM
NM
Once the parts have been added to the worksheet the first stage of any analysis is
an attempt at part reduction by reducing the number of components that must be
assembled and then to ensure that the remaining components are easy to assemble.
In order to aid the identification of those components which are candidates for
elimination or combination with other components three simple criteria are used:
a) During operation of the product, does the part move relative to all other parts
already assembled? Only gross motion should be considered - small motions that
can be accommodated by elastic hinges, for example, are not sufficient for a
positive answer.
b) Must the part be of a different material that or be isolated from all other parts
already assembled? Only fundamental reasons concerned with material
properties are acceptable.
19
c) Must the part be separate from all those already assembled because other wise
necessary assembly or disassembly of other separate parts would be impossible?
If a part is justified by any one of these reasons, it is deemed to be a necessary part
and receives a 1 in the worksheet. If justification is not possible, then that part is nonessential, receiving a 0 in the worksheet, and should be designed out or combined with
another essential part.
The second stage of the analysis is to examine the handling and insertion of each
component part. For manual assembly a two digit handling code and a two digit
insertion code are identified from synthetic data tables. The tables categorise
components with respect to their features for handling such as size, weight, and required
amount of orientation. For insertion, categories are for aligning of the part, type of
securing method, and whether the part is secured on insertion or as a separate process.
These codes are then cross-referenced to identify the time for that operation from the
table. The codes and subsequent times are entered into the worksheet and used to
determine a number of metrics.
Assembly time (TM) is determined by summing the handling and insertion
times. Assembly cost (CM) is proportional to TM by a factor that accounts for wage rate
and overheads. Theoretical minimum number of parts (NM) is the summation of all
those essential parts categorised by a 1. Design efficiency is defined as the ideal
assembly time divided by the estimated assembly time. The ideal assembly time is given
by 3NM, where the 3 represents a handling time of 1.5 and insertion time of 1.5, for an
ideal component. The estimated assembly time is TM. Though costs and times are
determined care must be taken in the use of these values in an absolute sense, as with
other techniques values are best used for comparison of re-designs.
20
2.9.3
Lucas DFA
Lucas DFA method encompasses a functional analysis, a handling or feeding
analysis and a fitting analysis. The method involves the assigning and summing of
penalty factors associated with potential design problems similar to the Hitachi method
but with the inclusion of handling (or feeding) as well insertion. These penalty factors
are combined with an assembly sequence flow chart (Figure 2.1) and generate three
assemblability scores. The three scores; design efficiency, feeding/handling ratio and
fitting ratio are generated in three stages of the analysis. All components of an assembly
undergo functional analysis, categorising them into an A (essential) part or a B (nonessential) part. The design efficiency is derived from the ratio of essential parts to total
parts (A/(A+B)). A suggested target of 60% is to be aimed for. The feeding or handling
analysis examines each component with respect to a knowledge base to determine a
feeding index, these are then summed for the total assembly. The feeding index has a
threshold of 1.5 indicating that any greater score be considered for redesign for feeding.
The feeding ratio is the ratio of feeding index total to number of essential components,
and has its own threshold of 2.5. Fitting analysis follows the same formula as feeding,
utilising a knowledge base, determining a fitting index, and finally a fitting ratio. These
scores can then be compared to thresholds or values established for previous designs
21
Figure 2.1: Assembly sequence flow chart
22
2.10
EXAMPLES OF DFA METHODOLOGIES
There are three examples of DFA methodologies for each of the approaches.
All the examples are taken from their respective origin.
2.5.1
Redesign of a simple product using Hitachi Assemblability Evaluation
Method (AEM).
An illustration of a simple redesign procedure is shown in Figure 9, Figure 10
and Figure 11. It shows the original and two redesigns of a block attachment to a
chassis.
Step 1: (Original design)
Here it is necessary to attach a small block B, to a chassis A. The initial method, shown
in Figure 2.2, involves the use of bolt C.
Figure 2.2: Original design
23
Table 2.3: Evaluation score and the cost ratio of the original design
Set chassis A
Bring down B and
hold it to maintain
orientation
Fasten screw C
Part
Assemblability
Evaluation
Score
100
E
Assemblability
Evaluation
Score
Assembly Cost
Ratio
50
73
1
K
65
Step 2: (Redesign 1)
Examining the original design, the holding down to maintain orientation is the worst
individual evaluation score and the suggestion is that the need for holding be removed
by spot-facing the chassis shown in Figure 2.3. This gives an improved evaluation score
and cost ratio as a result of this (Table 2.4).
Figure 2.3: Redesign 1
24
Table 2.4: Evaluation score and the cost ratio of redesign 1
Set chassis A
Bring down B
(orientation is
maintained by spotfacing)
Fasten screw C
Part
Assemblability
Evaluation
Score
100
E
Assemblability
Evaluation
Score
Assembly Cost
Ratio
100
88
0.8
K
65
Step 3: (Redesign 2)
Here, the bolt has been removed and the block attached to the chassis by using a press
fit. The assembly evaluation score for the press fit is less than that for simple block
placement and reduces from 100 to 80 but, importantly, one part has been eliminated.
As a result, although the product evaluation score has not significantly improved (89
compared with 88), the assembly cost ratio has significantly improved because of the
reduced number of parts (Figure 2.4 and Table 2.5).
Figure 2.4: Redesign 2
25
Table 2.5: Evaluation score and the cost ratio of redesign 2
Set chassis A
Bring down and
pressfit block B
2.5.2
Part
Assemblability
Evaluation
Score
100
80
E
Assemblability
Evaluation
Score
K
Assembly Cost
Ratio
89
0.5
Redesign of a simple product using the Boothroyd-Dewhurst DFA method
Figure 2.5: Original design
26
Figure 2.5 shows a simple sub-assembly used in the construction of a gas-flow
meter. The objective is to analyse the design using the Boothroyd-Dewhurst method
with the intention of using the information obtained to create a new, easier-to-assemble,
less expensive sub-assembly. In this analysis only manual assembly will be considered.
For the redesign of an existing product, it will be assumed that the functional parts must
have the same dimensions and be made of the same materials.
Table 2.6: Manual assembly worksheet for the original design
part no
number
repeats
total
manual
min
assembly assembly number
time
cost
parts
remarks
6
2
6
1.2
0
nut
5
2
6
1.2
0
washer
4
1
4
0.8
1
plate
3
1
3
0.6
0
bearing housing
2
2
20
4
0
screw
1
-
-
-
-
complete assembly
39
7.8
1
Design efficiency = 3 * min parts / assembly time = 3 * 1 / 39 = 0.077
Table 2.6 shows a design for a manual assembly worksheet for the product shown in
Figure 2.5.
If at least two parts are necessary, these would have to be the bearing housing
and the plate, as these are both functional, and all the other parts merely fasteners. There
are many possibilities for joining the bearing housing to the plate using integral
fastening: one proposed solution is by the use of integral rivets as shown in Figure 2.6.
The worksheet for this solution is shown in Table 2.7.
27
Figure 2.6: Redesign 1
Table 2.7: Manual assembly worksheet for Redesign 1
part no
3
2
1
total
manual
min
number
assembly assembly number
repeats
time
cost
parts
remarks
1
1
-
3
0.6
1
bearing housing
4
0.8
0
plate
complete assembly
7
1.4
1
Design efficiency = 3 * min parts / assembly time = 3 * 1 / 7 = 0.428
The plate can be placed either way up, but it does have rotational asymmetry and
is ‘thin’. One solution is to have one axially-symmetric integral fastener as shown in
Figure 2.7. For this solution, the bearing housing cannot be improved since it still needs
to be assembled one way up, and one of two ways round, but the plate is now easier to
handle. The worksheet for this solution is shown in Table 2.8.
28
Figure 2.7: Redesign 2
Table 2.8: Manual Assembly Worksheet for Redesign 2
part
no
3
2
1
total
manual
min
number
assembly assembly number
repeats
time
cost
parts
1
1
-
remarks
3
0.6
1
bearing housing
3
0.6
0
plate
complete assembly
6
1.2
1
Design efficiency = 3 * min parts / assembly time = 3 * 1 / 6 = 0.5
29
2.5.4
Redesign of a drain pump assembly using Lucas DFA
Figure 2.8 and Figure 2.9 show how the Lucas method can show design
efficiency and the feeding/handling and fitting ratios and how redesigning a product can
improve them.
In design efficiency, the first Drain Pump design shows a poor design efficiency
of 4 essential parts out of 25 (16%). The second design reduces the number of parts to 6
with a resulting design efficiency of 66%.
A visual comparison between the two ASFs shows that the redesign is much
simpler to assemble. This is reflected in the difference between the two Fitting Ratios
(4.0 for the redesign compared to 19.9 for the original).
The redesign has reduced the number of components by getting rid of the bolts,
washers and nuts. These happen to attribute the higher feeding analysis scores (and
fitting) to the total (this makes sense because these tend to be difficult to assemble in
reality). As a consequence the feeding and handling ratio has reduced from 6.9 to 1.63.
30
Figure 2.8: Original drain pump assembly design
31
Figure 2.9: Redesign using the Lucas DFA method
32
2.6
Summary
There are three different types of DFA methodologies: Boothroyd Dewhurst,
Hitachi and Lucas which can be applied in a product. Each method had its on approach
and function ability that refers to their principle. All of these methods are not just
refered to quantitative measure but required human interpretation to retain the results
which refers to their unique cases. Knowledge and skills are important in using this
method in order to get a good result.
Boothroyd Dewhurst applies quantitative measures where each part of the
product is number according to its assemblability. At the end, all the numbers from each
parts are summarized to gain the overall measures of the original design. Then,
afterwards the product has to be redesigned by minimizing the parts in the original
products. Later, it will be measured again using the same technique earlier with the new
design. The overall value can be maximized if at the redesign stage the parts that
contribute to the highest score were to be highlighted. All these reflect back on the
knowledge and skills of the designer. Other methods, Lucas and Hitachi, applied the
same strategy but with different approaches.
CHAPTER 3
DESIGN FOR AUTOMATIC ASSEMBLY (DFAA) METHODOLOGY
3.6
Introduction
In automatic assembly, the various individual assembly operations are generally
carried out at separate workstations. For this method of assembly, a machine is required
for transferring the partly completed assemblies from workstation to workstation, and a
means must be provided to ensure that no relative motion exists between the assembly
and the workheads or robot while the operations is being carried out. As the assembly
passes from station to station, it is necessary that it be maintained in the required
attitude. For this purpose, the assembly is usually built up on a base or work carrier, and
the machine is designed to transfer the work carrier from station to station.
Generally the automatic assembly may be divided into two classes on the basis
of system configuration as shown in Figure 3.1:
DF2A
Fixed/ Hard
Automation
Robotic assembly/
Soft
Automation
Figure 3.1: Classification of Automatic Assembly
34
3.1.1
Fixed/ Hard automation
Fixed or hard automation is characterised by custom-built machiner 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.
According to Boothroyd (1994), the rules of product design used in this type of
automation are:
ƒ
minimize the number of parts.
ƒ
ensure that the product has a suitable base part on which to build the assembly.
ƒ
ensure that the base part has features that enable it to be readily located in a
stable
position in the horizontal plane.
ƒ
if possible, design the product so that it can built up in layers, each part being
assembled from above and positively located so that these is no tendency for it to
move under the action of horizontal forces during the machine index period.
ƒ
try to facilitate assembly by providing chamfers or tapers that help to guide and
position the parts in the correct position.
ƒ
avoid expensive and time-consuming fastening operations, such as screw
fastening, soldering, and so on.
Besides that, Boothroyd (1994) also stated that for rules of design parts in this
automation must:
ƒ
Avoid projections, holes, or slots that cause tangling with identical parts when
placed in bulk in the feeder. This may be achieved by arranging the holes or slots
to be smaller than the projections.
35
ƒ
Attempt to make the arts symmetrical to avoid the need for extra orienting
devices and the corresponding loss in feeder efficiency.
ƒ
If symmetry cannot be achieved, exaggerate asymmetrical features to facilitate
orienting or, alternatively, provide corresponding asymmetrical features that can
be used to orient the parts.
3.1.1
Robotic Assembly/ Soft automation
Robotic assembly or soft automation or 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.
Compared to humans, robots are extremely inflexible and stupid. However, they can be
programmed to do one thing over and over again with high speed and accuracy
compared to humans.Although this type of assembly method can also have large capital
costs, its flexbility often helps offset the expense across many different products.
According to Boothroyd (1994) the design rules of robotic assembly are:
ƒ
Reduce part count – this is a major strategy for reducing assembly, manufacture,
and overhead costs irrespective of the assembly system to be used.
ƒ
Include features such as leads, lips, chamfers, etc., to make parts self-aligning in
assembly. Because of the relatively poor repeatability of many robot
manipulators – when compared to dedicated workhead mechanisms – this is a
vitally important measure to ensure consistent fault-free part insertions.
ƒ
Ensure that parts which are not secured immediately on insertion are selflocating in the assembly. For multistation robot assembly systems, or one-arm
single-station systems, this is an essential design rule. Holding down of
unsecured parts cannot be carried out by a single robot arm, and so special
36
ƒ
fixturing is required which must be activated by the robot controller. This adds
significantly to special-purpose tooling and, hence, assembly costs. With a twoarm single-station system, one arm can, in principle, hold down an unsecured
part while the other continues the assembly and fastening processes. In practice,
this requires one arm to change end-of-arm tooling to a hold-down device; the
system then proceeds with 50% efficiency while one arm remains immobile.
ƒ
Design parts so that they can all be gripped and inserted using the same robot
gripper. One major cause of inefficiency in robot assembly system is the need
for gripper or tool changes. Even with rapid gripper or tool change system, each
change to a special gripper and then back to the standard gripper is
approximately equal to two assembly operations. Note that the use of screw
fasteners always results in the need for tool changes since robot wrist can seldom
rotate more than one revolution.
ƒ
Design products so that they can be assembled in layer fashion from directly
above (z-axis assembly). This ensures that the simplest, least costly, and most
reliable 4 degree-of-freedom robot arms can accomplish the assembly tasks. It
also simplifies the design of the special-purpose workfixture.
ƒ
Avoid the need for reorienting the partial assembly or for manipulating
previously assembled parts. These operations increase the robot assembly cycle
time without adding value to the assembly. Moreover, if the partial assembly has
to be turned to a different resting aspect during the assembly process, then this
will usually results in increased workfixture cost and the need to use a more
expensive 6 degree-of-freedom robot arm.
ƒ
Design parts that can be easily handled from bulk. To achieve this goal avoid
parts that:
i. Nest or tangle in bulk
ii. Are flexible
iii. Have thin or tapered edges that can overlap or “shingle” as they move
along a conveyer or feed track
iv. Are so delicate or fragile that recirculation in a feeder would cause
damage
37
v. Are sticky or magnetic so that a force comparable to the weight of part
is required for separation
vi. Are abrasive and will wear the surfaces of automatic handling systems
vii. Are light so that air resistance will create conveying problems
ƒ
Is parts are to be presented using automatic feeders, then ensure that they can be
oriented using simple tooling. Follow the rules for ease of part orientation
discussed earlier. Note, however, that feeding and orienting at high speed is
seldom necessary in robot assembly, and the main concern is that the features
that define part orientation can be easily detected.
ƒ
If parts are to be presented using automatic feeders, then ensure that they can be
delivered in an orientation from which they can be gripped and inserted without
any manipulation. For example, avoid the situation where a part can only be fed
in one orientation from which it must be turned over for insertion. The will
require a 6 degree-of-freedom robot and special gripper, or a special 180° turn
delivery track – both solutions leading to unnecessary cost increases.
ƒ
If parts are to be presented in magazines or part trays, then ensure that they have
a stable resting aspect from which they can be gripped and inserted without any
manipulation by the robot. If the production conditions are appropriate, the use
of robots holds advantages over the use of special-purpose workheads and some
design rules can be relaxed. For example, a robot can be programmed to acquire
parts presented in an array – such as in a pallet or part tray which has been
loaded manually, thus avoiding many of the problems arising with automatic
feeding from bulk. However, when making economic comparisons, the cost of
manual loading of magazines must be taken into account.
38
3.7
Structure of DFAA
DFAA method is structured according to the design rules and guidelines used in
designing products for automatic assembly. It can be divided into two sections as
shown in Figure 3.2:
DFAA
Method
Product
Level
Part
Level
Figure 3.2: DFAA Method
3.2.1
Product Level
According to Stephan Eskilander (2001), product level is a design rules for the
studied object (module/product), He also suggested question for this part level which is
shown in Figure 3.3.
39
Product Level
Reduce number of
parts
Unique parts
Base object
Design base object
Assembly directions
Chain of tolerances
Parallel operations
Disassembly
Packaging
Figure 3.3: Suggested structure for Product level in the DFAA method
(Stephan Eskilander, 2001)
3.7.1.1 Reduce Number of Parts
The overall functionality of a product is influenced by the number of parts in a
product. The possibility for the number of parts to be reduced can be done by three of
these methods:
40
i.
integrated features and functions from several parts to a single part by
production methods such as casting, forging and injection molding.
ii.
reduce the number of fastening elements such as screws, bolts and pin. Snap
fits is a fastening features which can be considered due to its simpler
movements which can facilitate automatic assembly
iii.
considered disassembly, maintenance and service
Table 3.1 shows the evaluation of the part reduced in the product.
Table 3.1: The evaluation of the part reduced in the product
Reduce number of parts within each module. Too many parts
contribute to large work content within the module
Number of parts ≤20
9 points
20<Number of parts≤30
3 points
Number of parts>30
1 point
3.7.1.2 Unique Parts
Different parts required different types of assembly equipments. As a result,
standardized is important for parts in the product to minimize the unique parts that will
affect the automatic assembly process. Table 3.2 shows the evaluation of the unique
parts in the product.
Table 3.2: The evaluation of the unique parts in the product
Proportion of unique parts =Number of unique parts in the object
Total number of parts in the object
Proportion of unique parts <40%
9 points
40% ≤Proportion of unique parts ≤70%
3 points
Proportion of unique parts >70%
1 point
41
3.7.1.3 Base object
The first part of the product which the other assemblies can proceed from is the
base object. It has become a requirement to have a base component during automatic
assembly. Table 3.3 shows the evaluation of the base object of the product.
Table 3.3: The evaluation of the base object of the product
Base object is a first part that the rest of the assembly can proceed
from. All assembly operations are performed on the base object, which
leads to simple fixtures and few assembly directions
With base object
9 points
Without base object
1 point
3.7.1.4 Design base object
The design of the base object should be done so that it can be gripped, fixed and
transported without loosing its point of reference. Besides that, the base object should
have:
ƒ
radii and chamfers which can make it easily to be placed in its fixture.
ƒ
steady design placing in the fixture. Then, the guiding insertion of the holes and
pegs should be conical.
ƒ
simple contour which ease fixturing.
ƒ
stable centre of gravity
ƒ
do not shows a larger number of composition points
Table 3.4 shows the evaluation of the base object of the product.
42
Table 3.4: The evaluation of the design base object of the product
Design base objects for easy fixturing
The base object is designed in a way that no further fixture, besides for
9 points
the object itself, is needed for the rest of the assembly. The base object
does not need repositioning during assembly. One assembly direction
Assembling the module requires multiple fixtures that each has only
3 points
one fixed position. The base object has to be reoriented or transferred
between fixtures during assembly
Assembling the module requires one or multiple fixtures that have
1 point
several movable positions. The base object must be transferred
between and/ or repositioned in the fixtures during assembly.
3.7.1.5 Assembly directions
The assembly operations for a product should ideally occur from one
direction, which is from the above. Assembly direction from above is likely to be use
because it is much easier to assemble parts with the aid of gravity force during inserting
and fastening process. Table 3.5 shows the evaluation of the assembly directions of the
product.
Table 3.5: The evaluation of the assembly directions of the product
Assembly directions, totally in the whole product/ module
One assembly direction into a fixed base object
9 points
Two assembly directions into a fixed base object (alternatively one
3 points
assembly direction in a movable base object with two different fixed
positions).
Three or more assembly directions into a fixed base object
(alternatively assembly in a movable base object with several different
fixed positions).
1 point
43
3.7.1.6 Parallel operations
The total lead-time of an assembly procedure can be considerably shortened if
the assembly operations can be carried out in parallel. For that reason, a product
assembly should be designed to support a straight assembly sequence that does not
require sub-assemblies, but can be assembled in parallel if possible. Besides reducing
the lead-time, a parallel assembly process and a standardized set of parts may ensure
that all the variants of the product can be produced in the final assembly. Table 3.6
shows the evaluation of the parallel operations of the product
Table 3.6: The evaluation of the parallel operations of the product
Parallel operations according to the following example:
1
3
1
5
7
2
6
8
5
2
4
6
7
3
9
8
4
10
11
9
12
7
The assembly sequence to the left has parallel operations; the
9
sequence to the right has
10
parallel operations.
12
>50% parallel operations
9 points
0% < parallel operations ≤50%
3 points
No parallel operations
1 point
44
3.7.1.7 Chain of tolerances
The chain of tolerances or multiple tolerances should be minimized in the design
of a product to have more dependable assembly process in automatic assembly. It is
because automatic assembly systems have determined measures for grippers,
fixtures and etc, which all tolerances must be accordingly adjusted. Thus, the
assembly system will probably stop when any measure of the parts is out of tolerances
compatible with the tolerances of the assembly equipments. Table 3.7 shows the
evaluation of the chain of tolerances of the product
Table 3.7: The evaluation of the chain of tolerances of the product
Chain of tolerances should be minimized to have more reliable
assembly process
No chains of tolerances significant for the assembly process. Only the
9 points
tolerance of each individual part is significant
There are chains of two tolerances significant for the assembly process
3 points
in the module.
There are chains of three or more tolerances significant for the
1 point
assembly process in the module.
3.7.1.8 Disassembly
The ease of disassembly of a product has to be considered qualitatively in
automatic assembly. There is no evaluation criterion for disassembly found directly
applicable. A product that is easy to disassemble also determines that it is serviceable
and easy to adjust. Therefore, simple standard fastening methods should be
implemented and number of parts should be reduced in order to achieve easier and
45
cheaper disassembly process. There are some important guidelines that have to be
considered related with this design rule which are:
i.
Hazardous substances in a product that can cause difficulties in
disassembly
and re-usability, should be avoided.
ii.
Valuable parts must be designed to be easily removed for further re-use.
iii.
Large range of materials in a product should be avoided.
3.7.1.9 Packaging
The packaging of a product should have a minimum of material and space.
Besides that, a product packed should remain in the right orientation until it is delivered
to the customer. Eventually, there is no evaluation criterion for packaging found directly
applicable.
3.2.3
Part Level
Stephan Eskilander (2001) stated that part level is a design rules for each part of
the module/ product. He suggested question for this part level which is shown in
Figure 3.4.
46
Part Level
Need to assemble part?
Level of defects
Orientation
Non-fragile parts
Hooking
Centre of gravity
Shape
Weight
Length
Gripping
Assembly motions
Reachability
Insertion
Tolerances
Hold assembled parts
Fastening method
Joining
Check/adjust
Figure 3.4: Suggested structure for Part level in the DFAA method
(Stephan Eskilander, 2001)
47
3.2.2.1 Need to Assemble Part?
The aim of a design rule is to simplify the product through the reduction total
number of separate parts. This can be also considered as an approach to the integration
of parts. According to the DFMA methodology, there are three criteria used to identify
the parts that are possible to be eliminated or integrated [1]:
1. During operation of the product, does the part move relative to all other parts
already assembled?
2. Must the part be of a different material than or be isolated from all other parts
already assembled?
3. Must the part be separate from all other parts already assembled because
otherwise necessary assembly or disassembly of other separate parts would
be impossible?
If any of these questions are answered with a “yes”, it shows that the part is
supposedly necessary for the assembly. If all three questions are answered with “no”,
then the part has no reason to exist and should be eliminated or integrated with others.
Table 3.8 shows the evaluation for need to assemble part of each part.
Table 3.8: The evaluation need to assemble part of each part
Need to assemble part? The question describe above have to be
answered for evaluation. A part that does not perform a relative
motion has to be of another material or must be separated in order for
assembly /disassembly reasons to be eliminated or integrated
The path has reasons for being separate (at least one “yes” to the three
9 points
questions)
The part should be eliminated/ integrated (all three questions answered
with “no”) but the part is still a separate part in the product.
1 point
48
3.2.2.2 Level of Defects
The parts and components that are produced within the company and
standardized parts must be reliable with low level of defects. The defects in terms of
functionality and geometrical should be eliminated. Table 3.9 shows the evaluation for
level of defects of each part.
Table 3.9: The evaluation level of defects of each part
Level of defects of parts that are to be assembled. Geometric defects
that might cause unscheduled stops in an automatic assembly system
should be avoided, or parts with functional defects
P<0,1%
9 points
0,1% ≤ P ≤1,5%
3 points
P>1,5%
1 point
3.2.2.3 Orientation
The need for orientation should be minimized but when it is needed, the parts
should be designed with an easy orientation to produce high reliability. Table 3.10
shows the evaluation orientation of each part.
Table 3.10: The evaluation for orientation of each part
Orientation. If a part should be delivered oriented, cost and
uncertainty in the process would be eliminated.
No need for re-oriented of the part
9 points
Part is partly oriented, but needs final orientation
3 points
Part orientation needs to be re-created
1 point
49
3.2.2.4 Non-Fragile parts
The non-fragile parts are necessary for automatic feeding. In automatic
assembly, vibratory feeders are widely used as feeding solution, but they require nonfragile parts with center of gravity and shapes that can be used for such feeding
system. Table 3.11 shows the evaluation for non-fragile parts.
Table 3.11: The evaluation for non-fragile parts
Feeding often requires non-fragile parts
Part is not fragile
9 points
Part can be scratched, which is not acceptable
3 points
Part can not fall without deforming
1 point
3.2.2.5 Hooking
The parts that have the criteria below should be avoided in automatic assembly:
ƒ
nested, tangled and hooked up together when storing in bulk is highly not
suggested in automatic assembly.
ƒ
projecting shapes, holes, gaps or cut-outs should be avoided.
ƒ
made using sticky and magnetic materials
ƒ
fed in tape or ribbons
Table 3.12 shows the evaluation for hooking of each part.
Table 3.12: The evaluation for hooking of each part
State during feeding, hooking: There should be no risk of parts
Man.
hooking into each other for example a bulk vibration feeder
ref time
Parts cannot hook to each other and tangle up.
9 points
0s
Parts can hook to each other and tangle up
1 point
0,7s
50
3.2.2.6 Centre of Gravity
The center of gravity in a part should be correctly positioned to simplify
orientation and aid feeding process in automatic assembly. The center of gravity
should give the part a very stable state of rest, and should be positioned very
eccentrically. Table 3.13 shows the evaluation for centre of gravity of each part.
Table 3.13: The evaluation for centre of gravity of each part
Centre of gravity for the part should be positioned for use in feeding.
Drop the part repeatedly on a table to determine its state of rest.
Simple orientation often means reliable and cost effective feeding
Part has a stable state of rest and orients itself with correct side
9 points
upwards.
Part has a stable state of rest but orients itself with wrong side
3 points
upwards.
Part has an unstable state of rest and orients itself with different sides
1 point
upwards.
3.2.2.7 Shape
To facilitate orientation in automatic assembly, there are some factors that
should be considered regarding part shape:
ƒ
Shapes that can be used as means for orientation should be placed in the outer
contours and preferably well visible.
ƒ
Include obstacles for rotation in the contour.
ƒ
Surfaces on the parts should be designed suitably like surfaces with clear
contrast to be easily identified by the vision system in automatic assembly.
ƒ
Symmetrical shapes are encouraged. If part impossible to be symmetrical in
51
shape, it is better to make it more asymmetrical. Asymmetries in a part should
not be bigger than 0.1 of the diameter or 0.1 of the length to simplify
orientation in a feeder.
ƒ
Part should have as few vital orientations as possible to simplify orientation.
The evaluation criterion used for this design rule is based on the total sum of
the alpha and beta rotational symmetries of the part [1]. Alpha symmetry, α depends
on the angle through which a part must be rotated about an axis perpendicular to the
axis of insertion, to repeat its orientation. Beta symmetry, β depends on the angle
through which a part must be rotated about the axis of insertion, to repeat its
orientation. Table 3.14 shows the evaluation for shape of each part.
Table 3.14: The evaluation for shape of each part
Shape of a part is the sum of α- and β-symmetry. Symmetrical
Man.
ref. time
parts decrease the need for unique orientation
α + β <360
9 points
0s
360≤α + β <540
3 points
0,6s
540≤α + β ≤720
1 point
0,9s
3.2.2.8 Weight
The part that is too heavy requires larger and stiffer equipment and can cause
risk
for impact stress. However, part that is too light can also cause problems with
adhesion forces. Therefore, the weight of a part should be designed within the right
balance to facilitate automatic assembly. Table 3.15 shows the evaluation for weight of
each part.
52
Table 3.15: The evaluation for weight of each part
Weight, of the part. This affects the choice of equipment
Man.
ref. time
0,1g ≤G ≤ 2kg
9 points
0s
0,01g ≤G < 0,1g or 2kg <G ≤ 6kg
3 points
1,5s
G< 0,01g or G > 6kg
1 point
3s
3.2.2.9 Length
The length of a part affects the design of assembly equipments like feeders,
grippers and fixtures. An automatic assembly system must be adjusted to the size of
parts that are to be assembled. Therefore, the length of a part should also be
considered critically like the weight mentioned just now. Table 3.16 shows the
evaluation for length of each part.
Table 3.16: The evaluation for length of each part
Length. The length of a part is the longest side of an enclosing
Man.
prism. This affects the choice of equipment
ref. time
5 mm ≤ L ≤ 50 mm
9 points
0s
2 mm ≤ L < 5 mm or 50 mm < L ≤ 200 mm
3 points
0,7s
L < 2 mm or L > 200 mm
1 point
1,2s
3.2.2.10
Gripping
A gripper is less flexible and usually requires more space than human hand.
Therefore, all parts must be designed for ease of gripping in automatic assembly. There
are some aspects related to the design for easy gripping should be considered as below:
53
ƒ
The surface for gripping should be possible to be use as final positioning of part
when it is being gripped.
ƒ
The gripping system should be designed in a way that many parts can be gripped
with the same gripper. Special surfaces for gripping parts are not always
needed, but sometimes necessary to avoid multiple grippers.
ƒ
Must use the surfaces for gripping that ensure that the part always is positioned
the same way and avoid designing soft and easily deformed parts that are
difficult to grip with mechanical grippers.
ƒ
The outer and inner contours of parts should be gripper friendly with defined
gripping surfaces.
ƒ
The ability to grip a part increases if the part is symmetrical, compact, nonslippery and in constant shape.
ƒ
Round parts should be designed with the center line to be gripped coaxial to
the gripper or the center line of the robot.
ƒ
The center of gravity for the part should be as close as possible to the gripping
position.
ƒ
Equally large parts to be assembled should be designed in one sequence, in
order to lower the number of gripper changes.
Table 3.17 shows the evaluation for gripping of each part.
Table 3.17: The evaluation for gripping of each part
Gripping is simplified if there are defined surfaces with determined
Man.
geometry for use. Soft parts are difficult to grip with a mechanical
ref. time
gripper since the parts can deform from the forces in the gripper.
Part has surfaces for gripping and can be gripped with the same
9 points
0s
3 points
0s
1 point
1s
gripper as the previous part.
Part has surfaces for gripping, but requires a new, unique gripper
that could not be used for the previous part, Part has surfaces for
gripping and can use the same gripper as used earlier, but not for
the previous part.
Part has surfaces for gripping or is flexible.
54
3.2.2.11
Assembly Motion
The assembly motions involved in automatic assembly should be as simple as
possible where all parts should be possible to assemble with one hand. Manual assembly
with one hand will be similar to automatic assembly. Pushing a part in place is the
fastest
assembly motion, followed by pulling, sliding and rotating. Ideally, a part should be
assembled by only one motion. Combination of these assembly motions should be
avoided. Table 3.18 shows the evaluation for assembly motion of each part.
Table 3.18: The evaluation for assembly motion of each part
Assembly motion (during insertion) will be faster, the simpler they
Man.
are.
ref. time
Assembly motion consists of a pressing motion with one part being
9 points
0s
3 points
0,5s
1 point
0,8s
assembled to already assembled parts.
Assembly motion consists of further motions than pressing motion
with one part.
Assembly motion is an operation with multiple movable parts that
simultaneously are assembled already assembled parts with other
motions than pressing motion.
3.2.2.12
Reachability
The parts designed are necessary to have enough space for assembly equipments
during insertion, fastening and any other operations. Avoided the obstacles that can
cause difficulties to the motions of the equipments. Table 3.19 shows the evaluation for
reachability of each part.
55
Table 3.19: The evaluation for reachability of each part
Reachability for assembly operation should not be limited. All
Man.
parts should be inserted in the same direction.
ref. time
No restrictions or problems for reaching when fitting the part
9 points
0s
Reachability is limited. Other assembly direction than previous part
3 points
4,5s
Reachability is limited and requires special tools or grippers to
1 point
7s
perform the assembly operation. Other assembly direction than
previous part.
3.2.2.13
Insertion
Insertion can be simplified by using chamfers and guiding surfaces. Besides that,
small gap should also be allowed within the part to compensate for tolerances that are
not
ideally derived., friction should be minimized between parts during assembly,
since high friction might require more complicated and expensive assembly
equipments. Less complex insertion process should be implemented to facilitate
automatic assembly. Table 3.20 shows the evaluation for insertion of each part.
Table 3.20: The evaluation for insertion of each part
Insertion is simplified if there are chamfers or other guiding
Man.
surfaces, e.g. an edge that can be used as a mechanical guide for the
ref. time
fitting operation, in the part.
Chamfers exists to simplify the insertion operation
9 points
0s
No chamfers, but other guiding surfaces simplifies the insertion
3 points
0,2s
1 point
0,5s
operation
No chamfers or other guiding surfaces
56
3.2.2.14
Tolerances
The tight tolerances for parts should be avoided if possible. It is because they can
lead to higher manufacturing costs and higher risk of failure during insertion
operations in automatic assembly. Table 3.21 shows the evaluation for tolerances of
each part.
Table 3.21: The evaluation for tolerances of each part
Tolerances for insertion operations, for example the distance
Man.
between a peg and a hole during insertion or whenever there is
ref. time
manipulation of parts relative to each other. Too small tolerances
increase the risk of failure during insertion and the system could
stop.
Tolerance> 0,5 mm
9 points
0s
0,1 mm ≤ Tolerance ≤ 0,5 mm
3 points
0,2s
Tolerance < 0,1 mm
1 point
0,4s
3.2.2.15
Holding Assembled Parts
To holding assembled parts is required if any parts cannot keep its orientation
and position after assembly. A part should be designed with features that can enable it to
maintain its position without any external assistance. The features are like snap fits,
support and secure placing of the center of gravity. Table 3.22 shows the evaluation for
holding assembled parts.
57
Table 3.22: The evaluation for holding assembled parts
Holding assembled parts is necessary if parts cannot keep
Man.
orientation and position after assembly. Parts that are secured
ref. time
immediately, i.e. does not lose orientation or position if the
assembly is turned up side down, ensures a more reliable assembly
process
Part is secured immediately at insertion
9 points
0s
Part keeps orientation and position, but is not secured
3 points
0s
Part must be held after insertion to keep orientation and position
1 point
4s
3.2.2.16
Fastening Method
The number of fastening elements in a product should be minimized by
integration and standardization. Assembling fasteners should entail simple motions like
snap fits, and their assembly direction should be identical to each other. Table 3.23
shows the evaluation for fastening method of each part.
Table 3.23: The evaluation for fastening method of each part
Fastening method. How is the analyzed part itself fastened?
Man.
ref. time
No fastening method at all (the part is placed on or in an already
9 points
0s
Screwing-or pressing operations.
3 points
3s
Adhesive fastening methods, welding, soldering, riveting
1 point
8s
assembled part), or only snap fits.
58
3.2.2.17
Joining
To simplify automatic assembly process, a part should be designed for easy and
quick fitting, joining and securing, in order. Extra equipments like screwdrivers
should not be needed to fit the part into place. Take for instance like snap fits, it does
not need any tools to fasten the part. All joining involved should be from the same
direction, preferably from above with the aid of gravity. Table 3.24 shows the
evaluation for joining of each part.
Table 3.24: The evaluation for joining of each part
Joining : Extra equipment or tools (e.g. press tools or screwdrivers)
Man.
should not be needed to fit the part into place.
ref. time
No extra equipment is needed
9 points
0s
Extra equipment or tools are needed to fit the part in place and the
3 points
2s
1 point
3s
extra operation is performed in assembly direction.
Extra equipment or tools are needed to fit the part in place and the
extra operation is not performed in assembly direction.
3.2.2.18
Check/Adjust
The adjustment operations are difficult and expensive to be automated. Every
extra operation for checking or adjusting of part should be avoided if possible. “Poka
yoke” should be implemented to eliminate the risk of assembling in the wrong way. In
cases where adjustment cannot be avoided, adjustments of the product should be
performed separately after automatic assembly. Parts should be designed to ensure
clear controls with as simple sensors as possible. Table 3.25 shows the evaluation for
check/ adjusts of each part.
59
Table 3.25: The evaluation for check/ adjusts of each part
Check/Adjust is not needed if the product is designed according to
Man.
“poka yoke”, i.e. it is impossible to assemble the part in more than
ref. time
one way. Every extra operation for checking or adjusting is extra
work and a symptom of a design that is not quite satisfactory.
Unnecessary to check if part is in place
9 points
0s
Necessary to check if part is in place or assembled correctly
3 points
1s
Necessary to adjust or re-orient part.
1 point
2s
3.8
Applications of DFAA
The application of DFAA is applicable in two ways, one is design and evaluation
during early product development and the other one is redesign and evaluation of an
existing product.
3.8.1
Design and Evaluation During Early Product Development
There are two cases that can be mentioned here in this application. One if there
is a modular concept for the product but the other one is if there is no any modular
concept. How it is done?
For the first case, when there is a modular concept then the product developers
can continue with the detailed design of the module. After that, the design team can start
60
using DFAA method at the product level that included the design rules for the whole
object. Next step of the process is to go on with analyzing and designing each part of the
object. Design rules are structure in a basic assembly sequence is given to the user of
DFAA method. The users are free to go over back and forth in the method.
For the second case, when there is no modular concept, the product concept can
be taken as a modular concept. The process start at product level and by applying DFAA
method within the limited section of the product or a subassembly the procedure is still
useful.
3.3.2
Redesign and Evaluation of an Existing Product
For this application, the structure of the object must be analyzed before the
attempt to use DFAA method during redesign process. The assembly sequence is
determined by the product structure and every object that is analyzed, the assembly
sequence will start at the base object. The remaining parts should be assembled on the
base part without interference but if it happened, the object can be broken into
subassemblies.
Then, the object are analyzed using the evaluation sheet of product level
continue by part level. Concurrent with working the method, discussion and suggestion
for redesign can be recorded together with the analysis result for documentation. If there
is any new or other matters arising during the process must be added to the DFAA
method to prevent any mistakes.
61
3.9
Evaluation Philosophy and Criterions of DFAA
The evaluation philosophy that is used in DFAA is a qualitative evaluation. The
principles of this evaluation is a guide to the process adapted solution and which the
aspects involved here is critical and should not be overlooked. For intended users of the
method, they are required to avoid the unwanted solutions.
The evaluation criteria are scheme with a level point which is derived from the
SINTEF method, DFA House, Hitachi AEM and Sony DAC method. The level point’s
scheme is according to Modular Function Deployment (MFD) method is:
ƒ
Nine (9) points for best solution from an automatic assembly view
ƒ
Three (3) points for an acceptable, but not completely satisfactory solution
from an automatic assembly view
ƒ
One (1) points for unwanted from an automatic assembly view. Before
manufacturing, these solutions should be redesigned.
All this points are placed into the evaluation sheet for the product level
(Table 3.26) and part level (Table 3.27) according to design rules stated in section 3.2.
Table 3.26: Evaluation sheet for Product Level
PRODUCT LEVEL
Reduce
Unique
Base
Design
Assembly
Parallel
Chain of
number of
parts
object
base
directions
operations
tolerances
parts
Object/Product/Module
objects
SUM
62
Table 3.27: Evaluation sheet for Part Level
Part Level
SUM
Check/Adjust
Joining
Fastening method
Holding assembled method
Tolerances
Insertion
Reachability
Assembly motion
Gripping
Length
Weight
Shape
Centre of gravity
Hooking
Fragile parts
Orientation
Level of defects
Need to assemble part?
Number of identical parts
List of all parts
Then these points are summarized at the end of the procedure. The total score of
the product is divided with maximum score:
100 ×
3.10
Total score for the evaluated product
= DFA2 index in %
Maximum ideal score
Summary
DFAA method is divided into two levels, product and part levels. For product
level analysis, the evaluation is done on the whole product meanwhile for part level
analysis, the evaluation is done on each part of the product. Along with the evaluation,
each analyses are given the design rules which will helps the designer to improve the
design of their product.
CHAPTER 4
PRODUCT DETAIL FOR OLD DESIGN
4.5
Introduction
The selected product case study for this report is a three (3) pin wall socket
as shown in Figure 4.1. This product is used to supply electrical energy to electrical
appliance in any place.
(a)
(b)
Figure 4.1: (a) Front view (b) Back view
of 3 pin wall socket
64
4.6
Product Specification
The 3 pin wall socket specification contain the quantity, material, functions and
critiques for each part of the product. All this specification is shown in Table 4.1:
Table 4.1: Three (3) Pin Wall Socket Specification
Part
Description
Qty
Material
Function
Critique
As a base for the
Standard
socket connection
size
No.
1
2
Base socket 3 pin
Switch on/off
1
1
Plastic
Plastic
To switch on/ off the
power
3
Panel 3 pin
1
Plastic
To convert the 3 pin
holes
4
5
6
Spring
Cover socket 3 pin
Life plate
1
1
1
Standard
size
Standard
size
Carbon
To draw the panel 3
Steel
pin up and down
size
Plastic
As a cover for the
Can be
Copper
Standard
socket
neglected
To connect electricity
Standard
from switch on/off to
size
life wire
7
Life Clamp
1
Carbon
To clamp the life wire
Steel
8
Life Screw ∅6 X 11
1
Carbon
size
To hold the life wire
Steel
9
Life U Plate
1
Copper
Standard
Can be
neglected
To connect panel 3 pin
to life wire
Standard
size
65
Table 4.1: Three (3) Pin Wall Socket Specification (Continued)
10
Connector panel 3
1
Copper
pin
11
Plate switch on/off
To connect U plate
and plate switch on/off
1
Copper
Standard
size
To connect between
Standard
switch on/off and life
size
wire
12
Earth U plate
1
Copper
To connect between
Standard
earth wire and earth
size
plate
13
Earth Plate
1
Carbon
To connect between
Standard
Steel
earth wire and cover
size
socket 3 pin
14
15
Earth Clamp
Earth Screw ∅6 X 11
1
1
Carbon
To clamp the earth
Steel
wire
Carbon
To hold the earth wire
Steel
16
Neutral U Plate
1
Copper
Standard
size
Can be
neglected
To connect a point
Standard
from panel 3 pin to
size
neutral wire
17
Neutral Clamp
1
Carbon
To clamp neutral wire
Steel
18
Neutral Screw ∅6 X
1
20
Screw ∅5 X 12
Screw ∅6.5 X 12
size
To hold neutral wire
Steel
11
19
Carbon
2
2
Standard
Can be
neglected
Carbon
To hold base socket to
Steel
cover socket
neglected
Carbon
To hold socket to wall
Standard
Steel
Can be
size
66
4.3
Product Structure
This product is divided into three (3) parts which contain the base part, cover part
and screw φ6.2 X 23. The detail of this structure is shown in Figure 4.2:
3 pin wall socket
Base Part
Cover Part
Screw ∅6.5 X 2320
Base socket 3 pin1
Cover socket 3 pin5
Switch on/off2
Life components
Panel 3 pin3
Life plate6
Spring4
Life Clamp7
Screw ∅5 X 1219
Life Screw ∅6 X 118
Life U Plate9
Connector panel 3 pin10
Plate switch on/off11
Earth components
Earth U plate12
Earth Plate13
Earth Clamp14
Earth Screw ∅6 X 1115
Neutral components
Neutral U Plate16
Neutral Clamp17
Neutral Screw ∅6 X 1118
Figure 4.2: Three (3) Pin Wall Socket Structure of the Old Design
67
4.7
Product Assembly Operation Sequences
The assembly operation sequences of a wall socket is required to be done because
it will be needed in evaluation of the product and modifying to the proposed design. For
product assembly, every part will be assembled at least one type of assembly operation.
Every type of movement and direction of the parts done will be indicated and recorded.
4.7.1
Base Part
The base part of the 3 pin wall socket consists of five (5) parts: base socket1,
switch on/off2, panel 3 pin3, spring4 and screw ∅5 X 1219. For the first assembly process,
no tool is used to assemble all the components.
First, the spring4 is fixed into the panel 3 pin3. Then, insert this assemble part into
the base socket1. At the same time, the switch on/off2 is placed into the base socket1. As a
summary to this assembly process is shown as Figure 4.3:
Spring4
Panel 3 pin3
Switch on/off2
Base socket 3 pin1
Figure 4.3: Summary of the Assembly Process for Base Part
68
Figures 4.4 (a) and (b) show the base part before and after being
assembled to give a clear view of each part.
Base socket 3pin1
Switch on/off2
Spring4
Panel 3 pin3
(a)
(b)
Figure 4.4: (a) Before assembled (b) After assembled
for base part
69
4.7.2
Cover Part
The cover part consists of fourteen (14) parts: cover socket 3 pin5, life
plate6, life clamp7, life screw φ6 X 118, life U plate9, cnnector 3 pin10, plate switch
on/off11, earth U plate12, earth plate13, earth clamp14, earth screw φ6 X 1115, neutral U
plate16, neutral clamp17 and neutral screw φ6 X 1118. The assembly process for each part
in the cover part requires different tools or no tool at all.
The assembly process for this cover part can be divided into three assemblies
processes. These assemblies are shown below:
a)
Life Assembly Parts
Firstly, the life plate6 is insert into the base socket 3 pin5. Then the life
clamp7 is fix into its part on the base cover socket 3 pin5. Later, by using
a screw driver, tighten the screw ∅6 X 118 into the life clamp7. Afterwards,
allocate the plate switch on/off11 on the base socket 3 pin5 and the life U
plate9. Lastly, place the connector 3 pin10 on the top of the life U plate9.
b)
Earth Assembly Part
Insert the earth U plate12 into the base cover socket 3 pin5. Then, fix the earth
clamp14 into its location and take a screw driver to tighten the earth screw ∅6
X 1115 into the earth clamp14. Afterwards, allocate the earth plate13into the
earth clamp14.
c)
Neutral Assembly Parts
Fix the neutral U plate16 into the base cover 3 pin5 and then allocate the
neutral clamp17 into its allocation on the base cover 3 pin5. Later, tighten the
neutral screw ∅6 X 1118 with a screw driver into the neutral clamp17.
As a summary to these assemblies processes are shown as Figure 4.5:
70
Life plate6
Earth U plate12
Neutral U plate16
Life clamp7
Earth clamp14
Neutral clamp17
Life screw
∅6 X 118
Earth screw
∅6 X 1115
Neutral screw
∅6 X 1118
Plate switch
on/off11
Earth plate13
Life U plate9
Connector panel 3 pin10
Cover socket
3 pin5
Figure 4.5: Assembly Sequences for Cover Part
Figures 4.6 (a) and (b) show the cover part before and after being assembled to
give a clear view of each part.
71
Earth Screw ∅6 X 1115
Screw ∅5 X 1219
Earth Clamp14
Life Screw ∅6 X 116
Life Clamp7
Earth Plate13
Plate switch
on/off11
Earth
LifeUClamp
Plate12
Life Plate6
Neutral Screw ∅6 X 1118
Neutral
Life Clamp
Clamp17
Cover socket
3 pin5
Neutral U Plate16
Life U Plate9
Screw ∅5 X 1219
(a)
(b)
Figure 4.6: (a) Before assembled (b) After assembled
for cover part
Connector
panel 3 pin10
72
4.8
Summary
The product detail of the old design which is the 3 pin wall socket has been done
in this chapter. The detail consists of the product specification and structure. In product
specification, it explained on the material, quantity and the critique of each part of the
product. For product structure, it defined the overall structure of the product with the
assembly operation sequences of the product.
The product is divided into 3 parts: base part, cover part and screw ∅6.5 X 23
where each part has their own components to be considered during the assembly process.
The total number of parts in this product is 20 which included the unique components and
screws which can be redesigned back to give a good impact to ADE later on.
73
CHAPTER 5
EVALUATION OF THE ORIGINAL DESIGN
5.4
Introduction
For this product, 3 pin wall socket, the DFAA application that is used is the
redesign and evaluation of an existing product. First step is the structure of the 3 pin wall
socket must be analyzed before the attempt to use DFAA method during redesign
process. The assembly sequence has been determined by the product structure and every
object that is analyzed, the assembly sequence will starts at the base object. All this
information can be seen in Chapter 4.
Now is the second step of the method, the object is analyzed using the evaluation
sheet of product level continue by part level. The product level is done first because the
analysis is done on the whole product meanwhile for part level it is done on each part of
the product.
For both level, the evaluation points system is the same for each criterion. The
leveled point’s scheme is divided into three parts:
™ nine (9) points is for the best solution
™ three (3) points is for an acceptance, but not completely satisfactory
™ one (1) point is for unwanted solution
74
The applications of these points were applied in Tables 5.1and 5.2.
The evaluations were done according to the analysis as discussed in Chapter 3.
From this analysis, we will retain the result for ADE which will help us to improve our
product later on.
5.5
Product Level Evaluation of The Old Design
The product level evaluation is done on the whole product. All the numbers that
were included in Table 5.1 were taken from the data in the previous chapter 4 which
consist of the product specification and structure which are important to be included in
this product level evaluation. The result for the old design of a 3 pin wall socket is shown
in Table 5.1.
Table 5.1: Evaluation sheet of product level for the old design of 3 pin wall socket
PRODUCT LEVEL (BASE)
Reduce
Unique
Base
Design
Assembly
Parallel
Chain of
number of
parts
object
base
directions
operations
tolerances
3
9
9
parts
Object/Product/Module
9
SUM
objects
1
9
9
49
For product level evaluation of the base of 3 pin wall socket, Table 5.1 shows that
the evaluation were done according to the stated design rule as discussed in Chapter 3.
75
5.5.1
Reduce Number of Parts
The number of parts in this old design is 20. Therefore, according to the design
rule, the point given is 9.
5.5.2
Unique Parts
The unique parts of the old design refer to the ratio below:
Number of unique parts in the object 20
=
= 90.9%
Total number of parts in the objects 22
Due to this percentage, the point given for this design rule is 1.
5.5.3
Base Object
This old design has a part that can be used as the base object which the first part
where the rest of the assembly can be performed on. Therefore, according to the design
rule, the point given is 9.
5.5.4
Design Base Objects
The design base object does not required any orientation or fixturing during
assembly process. Therefore, according to the design rule, the point given is 9.
76
5.5.5
Assembly Directions
The assembly direction for this old design requires two assembly directions which
fix into the base object. Therefore, according to the design rule, the point given is 3.
5.5.6
Parallel Operations
The parallel operations is shown in the previous chapter in the product assembly
operation sequence where it can be shown in Figure 5.1:
77
Spring4
Panel 3 pin3
Switch on/off2
Life plate6
Earth U plate12
Life clamp7
Earth clamp14
Neutral clamp17
Life screw
∅6 X 118
Earth screw
∅6 X 1115
Neutral screw
∅6 X 1118
Plate switch
on/off11
Earth plate13
Life U plate9
Connector panel 3 pin10
Cover socket
3 pin5
Base socket 3 pin1
Screw ∅5 X 12
Screw∅5
∅6.5
X 19
23
Screw
X 12
Figure 5.1: Parallel Operations
According to Figure 5.1, the parallel operations is 12/20 = 60%. Therefore,
according to the design rule, the point given is 9.
Neutral U plate16
78
5.5.7
Chain of Tolerances
The chain tolerances should be minimized to gain a more dependable assembly
process. For this old design, there is no chain tolerance and all parts were taken as
individual tolerances. Therefore, according to the design rule, the point given is 9.
As a result from the evaluation done in the product level, the assembly index, A for the
old design:
Assembly index, A =
5.6
Sum
49
=
= 77.8%
Maximum po int s 63
Part Level Evaluation of The Old Design
The part level evaluation is done on each part of the product. The evaluation is
done in Table 5.2 which all the numbers that were included were taken from the data in
the previous chapter 4 which consist of the product specification and structure which are
important to be included in this part level evaluation. The result for the old design of 3
pin wall socket is shown in Table 5.2.
79
Table 5.2: Evaluation sheet of part level for the old design of 3 pin wall socket
Part Level
Need to assemble part?
Level of defects
Orientation
Fragile parts
Hooking
Centre of gravity
Shape
Weight
Length
Gripping
Assembly motion
Reachability
Insertion
Tolerances
Holding assembled method
Fastening method
Joining
Check/Adjust
Screw ∅6.5 X 23
Screw ∅5 X 12
9
1
9
9
1
1
9
9
9
9
1
1
3
3
3
3
9
9
3
3
3
3
1
1
3
3
3
3
1
1
3
3
3
3
9
9
Neutral Screw ∅6 X 11
Neutral Clamp
1
1
9
1
9
9
1
3
3
9
3
3
1
3
3
1
3
3
9
74
1
9
9
3
9
9
9
1
3
9
9
9
3
9
3
9
9
9
9
130
112
SUM
Number of identical parts
2
2
List of all parts
82
74
Neutral U Plate
1
9
9
1
9
1
1
1
3
9
9
9
3
9
3
9
9
9
9
Earth Screw ∅6 X 11
Earth Clamp
1
1
9
1
9
9
1
3
3
9
3
3
1
3
3
1
3
3
9
74
1
9
9
1
9
1
9
1
3
9
3
9
3
9
3
9
9
9
9
114
Earth Plate
1
1
3
1
9
9
9
1
3
9
3
9
9
3
3
9
9
9
9
108
Earth U plate
1
1
9
1
9
1
1
1
3
9
3
9
3
9
3
9
9
9
9
98
Plate switch on/off
1
1
3
1
9
9
9
1
3
9
3
9
9
3
9
9
9
9
9
114
Connector panel 3 pin
1
1
3
1
9
9
9
1
3
9
3
9
9
9
9
9
9
9
9
120
Life U Plate
1
1
9
1
9
1
1
1
3
9
3
9
3
9
3
9
9
9
9
98
Life screw ∅6 X 11
Life clamp
1
1
9
1
9
9
1
3
3
9
3
3
1
3
3
1
3
3
9
74
1
9
9
1
9
1
9
1
3
9
3
9
9
9
3
9
9
9
9
120
Life plate
1
9
3
1
9
9
9
1
3
9
9
9
9
3
9
9
9
9
9
128
Cover socket 3 pin
1
9
3
1
3
1
3
1
3
3
3
9
9
9
9
9
9
9
9
102
Panel 3 pin
1
9
3
1
3
1
3
1
3
9
3
9
9
3
3
9
9
9
9
96
Spring
1
9
1
1
3
1
1
9
1
9
3
3
3
3
1
9
9
3
9
78
Switch on/off
1
9
3
1
3
9
3
1
1
9
3
9
9
3
3
9
9
9
9
102
Base socket 3 pin
1
9
3
1
3
9
9
1
3
3
9
9
9
9
9
9
9
9
9
122
TOTAL SUM: 2020
Assembly Index New , ANew =
5.6.1
Total Number
2020
=
= 62.3%
Maximum Po int s * Number of Parts 162 * 20
Base Socket
The ADE score for the base socket is 75.3%. This percentage is considered
acceptable for automatic assembly. It is because the base has a stable state of rest and it
can orientate on its own with the correct side upwards.
80
5.6.2
Switch On/Off
The score for ADE on switch on/off is 63% which is low for automatic assembly.
It is because the switch on/off it is too light and it can not orientate on its own with the
correct side upwards
5.6.3
Spring
The score for ADE on spring is 48.1% which is low for automatic assembly.
It is because the spring can get tangle onto other parts and it do not has stable state of
rest.
5.6.4
Panel 3 Pin
The score for ADE on panel 3 pin is 59.3% which is low for automatic assembly.
It is because the panel 3 pin is too light and it can not orientate on its own with the correct
side upwards
5.6.5
Cover Socket
The score for ADE on cover socket is 63% which is low for automatic assembly.
It is because the cover socket can not orientate on its own with the correct side upwards
and can get tangle up with other parts.
81
5.6.6
Life Plate
The score for ADE on life plate is 79% which is acceptable for automatic
assembly. It is because the life plate has a stable state of rest and it can orientate on its
own with the correct side upwards.
5.6.7
Life Clamp
The score for ADE on life clamp is 74.1% which is acceptable for automatic
assembly. It is because the life clamp has a stable state of rest and it can orientate on its
own with the correct side upwards.
5.6.8
Life Screw φ6 X 11
The score for ADE on life screw φ6 X 11 is 45.7% which is low for
automatic assembly. It is because the life screw φ6 X 11 can not orientate on its own with
the correct side upwards and can get tangle up with other parts.
5.6.9
Life U Plate
The score for ADE on life U plate is 60.5% which is low for automatic assembly.
It is because the life U plate can not orientate on its own with the correct side upwards
and can get tangle up with other parts.
82
5.6.10 Connector Panel 3 Pin
The score for ADE on connector panel 3 pin is 74.1% which is acceptable for
automatic assembly. It is because the connector panel 3 pin has a stable state of rest and
it can orientate on its own with the correct side upwards.
5.6.11 Plate Switch On/Off
The score for ADE on plate switch on/ off is 70.4% which is acceptable for
automatic assembly. It is because the plate switch on/ off has a stable state of rest and it
can orientate on its own with the correct side upwards.
5.6.12 Earth U Plate
The score for ADE on earth U plate is 60.5% which is low for automatic
assembly. It is because the earth U plate can not orientate on its own with the correct
side upwards and can get tangle up with other parts.
5.6.13 Earth Plate
The score for ADE on earth plate is 66.7% which is low for automatic
assembly. It is because the earth plate can not orientate on its own with the correct side
upwards and can get tangle up with other parts.
83
5.6.14 Earth Clamp
The score for ADE on earth clamp is 70.4% which is acceptable for automatic
assembly. It is because the earth clamp has a stable state of rest and it can orientate on its
own with the correct side upwards.
5.6.15 Earth Screw φ6 X 11
The score for ADE on earth screw φ6 X 11 is 45.7% which is low for automatic
assembly. It is because the earth screw φ6 X 11 can not orientate on its own with the
correct side upwards and can get tangle up with other parts.
5.6.16 Neutral U Plate
The score for ADE on neutral U plate is 45.7% which is low for automatic
assembly. It is because the neutral U plate can not orientate on its own with the correct
side upwards and can get tangle up with other parts.
5.6.17 Neutral Clamp
The score for ADE on neutral clamp is 80.2% which is acceptable for automatic
assembly. It is because the neutral clamp has a stable state of rest and it can orientate on
its own with the correct side upwards.
84
5.6.18 Neutral Screw φ6 X 11
The score for ADE on neutral screw φ6 X 11 is 45.7% which is low for automatic
assembly. It is because the neutral screw φ6 X 11 can not orientate on its own with the
correct side upwards and can get tangle up with other parts.
5.6.19 Screw φ5 X 12
The score for ADE on screw φ5 X 12 is 45.7% which is low for automatic
assembly. It is because the screw φ5 X 12 can not orientate on its own with the correct
side upwards and can get tangle up with other parts.
5.6.20 Screw φ6.5 X 23
The score for ADE on earth screw φ6.5 X 23 is 50.6% which is low for automatic
assembly. It is because the earth screw φ6.5 X 23 can not orientate on its own with the
correct side upwards and can get tangle up with other parts.
5.7
Summary
The assembly index for product level of the old design 3 pin wall socket is
77.8% and the assembly index for part level of the old design 3 pin wall socket is
85
62.3%. From this result, we can conclude that the design is considered low for automatic
assembly and should has improvement in the new design.
86
CHAPTER 6
PROPOSED IMPROVEMENTS ON THE ORIGINAL DESIGN
6.4
Introduction
The proposed improvements were done after determining the product details and
evaluating the design. These improvements are required for the product details and the
ADE analysis further on.
6.5
Improvement of The Original Design
The improvements for the original design involved the eliminating and
combining components to reduce the part count in a product. These changes involved the
following components:
i.
Eliminating screws φ5 X 12 and changed to snap fits
ii.
Joining life plate, life U plate, connector 3 pin and panel 3 pin to become
one
iii.
Joining earth plate, and earth U plate to become one
iv.
Joining plate and screw φ6 X 11
87
6.5.1
Eliminating Screws φ5 X 12 and Changing to Snap Fits
The old design for the screw φ5 X 12 is to hold the cover socket to the base
socket. This is shown in Figure 6.1:
Screw φ5 X 12
Cover
Socket
Base
Socket
Figure 6.1: The location of screw φ5 X 12 on the 3 pin wall socket
For the proposed design, this screw is changed to snap fit which is easier to be done in
automatic assembly. The Figure 6.2 shows the proposed design of the snap fits.
88
Old design
New design
(a) Base Socket
Old design
New design
(b) Cover Socket
Figure 6.2: The Proposed Design from Screws φ5 X 12 to Snap Fits
6.5.2
Joining Life Plate, Life U Plate, Panel 3 Pin and Connector 3 Pin
The old design for life plate, life U plate, panel 3 pin and connector 3 pin are
separated parts as shown in Figure 6.3(a). In the proposed design, all these plates will be
combined to become a plate, life plate. See Figure 6.3(b).
89
Connector 3 Pin
Life Plate
Life U Plate
Panel 3 Pin
(a) Old design
Life Plate
(b) New design
Figure 6.3: The Proposed Design from Separate Life Plates to a Life Plate
6.5.3
Joining Earth Plate, and U Plate
The old design for earth plate and earth U plate are separated parts as shown in
Figure 6.4(a). In the proposed design, all these plates will be combined to become a
plate, earth plate. See Figure 6.4(b).
90
Earth Plate
Earth U Plate
(a) Old design
Earth Plate
(b) New design
Figure 6.4: The Proposed Design from Separate Earth Plates to an Earth Plate
6.5.4
Joining Clamp and Screw φ6 X 11
The old design for clamp and screw φ6 X 11 are separated parts as shown in
Figure 6.5(a). In the proposed design, all these plates will be combined to become a
plate, a clip. See Figure 6.5(b).
Clamp
Screw φ6 X 11
(a) Old design
Clip
(b) New design
Figure 6.5: The Proposed Design from Separate Clamp and Screw φ6 X 11 to a Clip
91
6.6
Summary
There are four improvements done on the original design. The improvements are
on eliminating or combining the components which will effect the product details,
structure and the ADE analysis. This improvements will give a good impact to the
automatic assembly system..
92
CHAPTER 7
PRODUCT DETAIL FOR PROPOSED DESIGN
7.6
Introduction
The product detail of the new design for 3 pin wall socket will be discussed using
the information gather from the previous chapter 6. This new design is to ensure that it
will be a good impact towards automatic assembly compared to the old design.
7.7
Product Specification
The new design of 3 pin wall socket specification contain the quantity, material,
functions and critiques for each part of the product. The total number of components for
the new design is 12. This number is much smaller compared to the old design which
consists of 22 components. All this specification is shown in Table 7.1.
93
Table 7.1: Specification of Three (3) Pin Wall Socket New Design
Part
Description
Qty
Material
Function
No.
1
Base socket 3 pin
1
Plastic
As a base for the socket connection
2
Switch on/off
1
Plastic
To switch on/ off the power
3
Panel 3 pin
1
Plastic
To convert the 3 pin holes
4
Spring
1
Carbon
To draw the panel 3 pin up and down
Steel
5
Cover socket 3 pin
1
Plastic
As a cover for the socket
6
Life plate
1
Copper
To connect electricity from switch
on/off to life wire
7
Life clip
1
Carbon
To hold the life wire
Steel
8
9
Earth Plate
Earth Clip
1
1
Carbon
To connect between earth wire and
Steel
cover socket 3 pin
Carbon
To hold the earth wire
Steel
10
Neutral U Plate
1
Copper
To connect a point from panel 3 pin to
neutral wire
11
Neutral Clip
1
Carbon
To hold the neutral wire
Steel
12
Screw ∅6.5 X 12
2
Carbon
Steel
To hold socket to wall
94
7.8
Product Structure
This product is divided into three (3) parts which consists of the base part, cover
part and screw φ6.2 X 23. The detail of this structure is shown in Figure 7.1:
Wall socket 3 pin
Cover part
Base part
Screw φ6.5 X2312
Cover socket5
Base socket1
Life components
Switch on/off2
Life plate6
Spring4
Life clip7
Panel 3 pin3
Earth components
Earth plate8
Earth clip9
Neutral
Neutral U plate10
Neutral clip11
Figure 7.1: Three (3) Pin Wall Socket Structure of the New Design
7.9
Product Assembly Operation Sequences
The assembly operation sequences of a wall socket is required to be done because
it will be needed in evaluation of the product and modifying to the proposed design. For
product assembly, every part will be assembled at least one type of assembly operation.
Every type of movement and direction of the parts done will be indicated and recorded.
95
7.9.1
Base Part
The base part of the new design of the 3 pin wall socket did not any changes
compared to the old design. This new design consists of five (5) parts: base socket1,
switch on/off2, panel 3 pin3, spring4 and screw ∅5 X 1219. For the first assembly process,
no tool is used to assemble all the components.
First, the spring4 is fixed into the panel 3 pin3. Then, insert this assemble part into
the base socket1. At the same time, the switch on/off2 is placed into the base socket1. As a
summary to this assembly process is shown as Figure 4.4:
Spring4
Panel 3 pin3
Switch on/off2
Base socket 3 pin1
Figure 7.2: Summary of the Assembly Process for Base Part
7.9.2
Cover Part
The cover part consists of seven (7) parts: cover socket 3 pin5, life
plate6, life clip7, earth plate8, earth clip9, neutral plate10 and neutral clip11. The assembly
process for each part in the cover part requires different tools or no tool at all.
The assembly process for this cover part can be divided into three assemblies
processes. These assemblies are shown on the next page:
96
d)
Life Assembly Parts
Firstly, the life plate6 is insert into the cover socket 3 pin5. Then the life
clamp7 is fix into its part on the base cover socket 3 pin5.
e)
Earth Assembly Part
Insert the earth plate8 into the cover socket 3 pin5. Then, fix the earth clip9 into
its location
f)
Neutral Assembly Parts
Fix the neutral plate10 into the cover 3 pin5 and then allocate the neutral clip11
into its allocation on the base cover 3 pin5.
As a summary to these assemblies processes are shown as Figure 7.3:
Life plate6
Earth plate8
Life clipp7
Earth clip9
Neutral plate10
Neutral clip11
Cover socket
3 pin5
Figure 7.3: Assembly Sequences for Cover Part
7.4.3
All Parts
From Figures 7.2 and 7.3, the parts afterwards will be assembled together using
two unit of screw φ6.5 X 23. The tool use for this assembly is a screw driver. Combining
both assemblies, the final assemblies is shown in Figure 7.4.
97
Spring4
Panel 3 pin3
Switch on/off2
Life plate6
Earth plate8
Neutral plate10
Life clipp7
Earth clip9
Neutral clip11
Base socket 3 pin1
Cover socket
3 pin5
Screw φ6.5 X 2312
Figure 7.4: Assembly Sequences for 3 Pin Wall Socket of the New Design
7.10
Summary
The product detail of the new design which is the 3 pin wall socket has been done
in this chapter. The detail consists of the product specification and structure. In product
specification, it explained on the material, quantity and the critique of each part of the
product. For product structure, it defined the overall structure of the product with the
assembly operation sequences of the product.
The product is divided into 3 parts: base part, cover part and screw ∅6.5 X 23
where each part has their own components to be considered during the assembly process.
The total number of parts in this product is 12 which included the unique components and
screws which can be redesigned back to give a good impact to ADE later on.
98
CHAPTER 8
EVALUATION OF THE NEW DESIGN
8.5
Introduction
The new design of the 3 pin wall socket is discussed in this chapter. The ADE
analysis which consists of the product level evaluation and part level evaluation is done
to prove that this new design is better compared to the old design.
8.6
Product Level Evaluation of The New Design
The product level evaluation is done on the whole product. All the numbers that
were included in Table 8.1 were taken from the data in the previous chapter 4 which
consist of the product specification and structure which are important to be included in
this product level evaluation. The result for the old design of a 3 pin wall socket is shown
in Table 8.1.
99
Table 8.1: Evaluation sheet of product level for the old design of 3 pin wall socket
PRODUCT LEVEL (BASE)
Reduce
Unique
Base
Design
Assembly
Parallel
Chain of
number of
parts
object
base
directions
operations
tolerances
1
9
9
9
9
parts
Object/Product/Module
9
SUM
objects
9
55
For product level evaluation of the base of 3 pin wall socket, Table 8.1 shows that
the evaluation were done according to the stated design rule as discussed in Chapter 4.
5.7.1
Reduce Number of Parts
The number of parts in this new design is 12. Therefore, according to the design
rule, the point given is 9.
5.7.2
Unique Parts
The unique parts of the new design refer to the ratio below:
Number of unique parts in the object 11
=
= 91.7%
Total number of parts in the objects 12
Due to this percentage, the point given for this design rule is 1.
100
5.7.3
Base Object
This new design has a part that can be used as the base object which the first part
where the rest of the assembly can be perform on. Therefore, according to the design rule,
the point given is 9.
5.7.4
Design Base Objects
The design base object do not required any orientation or fixturing during
assembly process. Therefore, according to the design rule, the point given is 9.
5.7.5
Assembly Directions
The assembly direction for this new design required one assembly directions
which fixed into the base object. Therefore, according to the design rule, the point given
is 9.
5.7.6
Parallel Operations
The parallel operations is shown in the previous chapter in the product assembly
operation sequence where it can be shown in Figure 8.1:
101
Spring4
Panel 3 pin3
Switch on/off2
Life plate6
Earth plate8
Neutral plate10
Life clipp7
Earth clip9
Neutral clip11
Cover socket
3 pin5
Base socket 3 pin1
Screw φ6.5 X 2312
Figure 8.1: Parallel Operations
As shown in the previous page, the parallel operations is 7/12 = 58.3%. Therefore,
according to the design rule, the point given is 9.
5.7.7
Chain of Tolerances
The chain tolerances should be minimized to gain a more dependable assembly
process. For this old design, there is no chain tolerance and all parts were taken as
individual tolerances. Therefore, according to the design rule, the point given is 9.
As a result from the evaluation done in the product level, the assembly index, A for the
old design:
Assembly index, A =
Sum
55
=
= 87.3%
Maximum po int s 63
102
8.7
Product Level Evaluation of The New Design
The part level evaluation of the new design for 3 pin wall socket is shown in
Table 8.2. The assembly index, A for the new design is 71.8%. The application of screw
is eliminated in the new design and changed to other design or snap fit. The application
of snap fit is done to ease the automatic assembly process.
Table 8.2: Evaluation sheet of part level for the new design of 3 pin wall socket
Part Level
N eed to assem ble part?
L evel of defects
O rientation
Fragile parts
H ooking
C entre of gravity
Shape
W eight
L ength
G ripping
A ssem bly m otion
R eachability
Insertion
T olerances
H olding assem bled m ethod
Fastening m ethod
Joining
C heck/A djust
2
1
1
9
9
9
1
3
9
9
9
9
9
9
3
3
3
3
9
9
3
9
3
3
9
9
9
3
3
3
3
9
3
3
3
9
9
9
120
Neutral Plate
1
9
9
3
9
9
9
1
3
9
9
3
9
3
3
9
9
9
9
124
Earth Clip
1
9
9
3
9
9
9
3
3
9
9
3
9
3
3
9
3
9
9
120
Earth Plate
1
9
9
3
9
9
9
1
3
9
9
9
9
3
3
9
9
9
9
130
Life clip
1
9
9
3
9
9
9
3
3
9
9
9
9
3
3
9
3
9
9
126
SU M
N um ber of identical parts
Screw ∅6.5 X 23
Neutral Clip
List of all parts
98
Life plate
1
9
9
3
9
9
9
1
3
9
3
9
9
3
3
9
9
9
9
124
Cover socket 3 pin
1
9
9
9
3
9
9
1
3
3
3
3
9
9
9
9
9
9
9
124
Panel 3 pin
1
9
9
3
3
9
9
1
3
9
3
3
9
3
3
9
9
9
9
112
Spring
1
9
3
3
3
1
1
3
1
9
3
3
9
3
1
9
3
9
9
82
Switch on/off
1
9
9
3
3
9
9
3
1
9
3
3
9
3
3
9
9
9
9
112
Base socket 3 pin
1
9
9
9
3
9
3
1
3
3
3
9
9
9
9
9
9
9
9
TOTAL SUM:
Assembly Index New , ANew =
Total Number
1396
=
= 71.8%
Maximum Po int s * Number of Parts 162 * 12
124
1396
103
8.7.1
Base Socket
The ADE score for the base socket is 76.4%. This percentage is considered
acceptable for automatic assembly. It is because the base has a stable state of rest and it
can orientate on its own with the correct side upwards.
8.7.2
Switch on/off
The ADE score for switch on/ off is 69.1%. This percentage is considered
acceptable for automatic assembly. It is because the switch on/ off has a stable state of
rest and it can orientate on less level of defects.
8.7.3
Spring
The ADE score for spring is 50.6%. This percentage is considered low for
automatic assembly. It is because the spring can get tangle onto other parts and it do not
has stable state of rest.
8.7.4
Panel 3 Pin
The ADE score for panel 3 pin is 69.1%. This percentage is considered
acceptable for automatic assembly. It is because the panel 3 pin has a stable state of rest
and it can orientate on less level of defects.
104
8.7.5
Cover Socket 3 Pin
The ADE score for cover socket 3 pin is 76.5%. The percentage is considered
acceptable for automatic assembly. It is because the cover socket 3 pin has a stable state
of rest and it can orientate on its own with the correct side upwards.
8.7.6
Life Plate
The ADE score for life plate is 76.5%. The percentage is considered
acceptable for automatic assembly. It is because the life plate has a stable state of rest and
it can orientate on its own with the correct side upwards.
8.7.7
Life Clip
The ADE score for life clip is 77.8%. The percentage is considered
acceptable for automatic assembly. It is because the life clip has a stable state of rest and
it can orientate on its own with the correct side upwards.
8.7.8
Earth Plate
The ADE score for earth plate is 80.2%. The percentage is considered
acceptable for automatic assembly. It is because the earth plate has a stable state of rest
and it can orientate on its own with the correct side upwards.
105
8.7.9
Earth Clip
The ADE score for earth clip is 74.1%. The percentage is considered
acceptable for automatic assembly. It is because the earth clip has a stable state of rest
and it can orientate on its own with the correct side upwards.
8.7.10 Neutral Plate
The ADE score for neutral plate is 76.5%. The percentage is considered
acceptable for automatic assembly. It is because the neutral plate has a stable state of rest
and it can orientate on its own with the correct side upwards.
8.7.11 Neutral Clip
The ADE score for neutral clip is 74.1%. The percentage is considered
acceptable for automatic assembly. It is because the neutral clip has a stable state of rest
and it can orientate on its own with the correct side upwards.
8.7.12 Screw φ6.5 X 23
The ADE score for screw φ6.5 X 23 is 60.5%. The percentage is considered
low for automatic assembly. It is because the screw φ6.5 X 23 do not has a stable state of
rest and it can not orientate on its own with the correct side upwards.
106
8.8
Summary
The assembly index for product level of the new design 3 pin wall socket is
87.3% and the assembly index for part level of the new design 3 pin wall socket is
71.8%. From this result, we can conclude that the design is considered acceptable for
automatic assembly. Even thought that, improvements can be done in future to get a
better evaluation.
107
CHAPTER 9
DISCUSSION
9.3
Introduction
The ADE analyses from the previous chapter showed that the product has four
improvements. The percentage of ADE is still below the expectation. The number of each
assembly can be reduced by reviewing the evaluation sheets.
For base socket 3 pin, all the parts are still required in the analyses but for cover
base socket the number parts is suggested to reduce from 15 to 7 parts. Assumptions for
both assemblies are made regarding the level of defects and orientation. The gripping
evaluation shows that a standard gripper surfaces are required. For insertions of some of
the parts will cause difficulties due to different insertion directions and also unavailable
chamfers on the parts.
Holding during the assembly process reflects a non-stable process in DFAA
analyses. Furthermore, the fastening method used here is the screwing operations which
required special equipments to perform the task.
Obviously, in the evaluation, for each criterion which scores “1” and “3” required
carefully considerations. It should be considered back whether it would be possibly
required improvement or not.
108
9.4
Comparison Between The Original Design and Proposed Design
The result obtained from the new design is better compared to the old design. The
main improvements can be seen in Table 9.1 which included the number of components
and number of unique components. Besides that, it also included the evaluation of the old
and new design in terms of product level and part level analysis.
Table 9.1: Comparison in Percentage between the Original Design and Proposed Design
Criteria
Original
New Design
Improvement
Design
Number of Components
22
13
40.9%
Number of Unique
20
12
40.0%
77.8%
87.3%
12.2%
62.3%
71.8%
15.2%
Components
Assembly Index for
Product Level
Assembly Index for Part
Level
These results can also be seen in Figures 9.1, 9.2 and 9.3 where the comparison
are shown graphically in these figures.
109
Number of Components
Comparison Number of Components
25
22
20
13
15
10
5
0
Original Design
New Design
Design Stage
Figure 9.1: Comparison Number of Components in Old and New Designs
Num ber of
Com ponents
Com parison Num ber of Unique Com ponents
25
20
15
10
5
0
20
12
Original Design
New Design
Design Stage
Figure 9.2: Comparison Number of Unique Components in Old and New Designs
110
Comparison between Assembly Index
100.0
80.0
Percentage
(%)
60.0
87.3
77.8
71.8
62.3
40.0
20.0
New Design
0.0
Original Design
Product
Part Level
Level
Assembly Index
Figure 9.3: Comparison between Assembly Index in Old and New Designs
9.4.1
Number of Components
According to Table 9.1, the main improvement is achieved in the number of
components. The number of components for the original design is 22 meanwhile the new
design is 13. There is a reduction of 9 components which contribute to 40.9%
improvements. The functionality of the original design has not been changed but with a
little bit of redesigning this is achieved. The improvements concentrate on eliminating
screw and changing it to snap fit and combining life, earth and neutral components. To
see more details on the action take on the old design, please refer to Table 9.2.
111
Table 9.2: Comparison between the Number of Components in Original Design and New
Design
Original No.
9.4.2
Original Component
1
Base socket (1)
2
Life plate (1)
3
Life U plate (1)
4
Connector 3 pin (1)
5
Plate switch on/off (1)
6
Life clamp (1)
7
Life screw φ6X11 (1)
8
Earth U plate (1)
9
Earth plate (1)
10
Earth clamp (1)
11
Earth screw φ6X11 (1)
12
Neutral U plate (1)
13
Neutral clamp (1)
14
Neutral screw φ6X11 (1)
15
Cover socket (1)
16
Action Taken
Include snap fit
New Component
New No.
Base socket (1)
1
Combine
Life plate (1)
2
Combine
Life clip(1)
3
Combine
Earth plate(1)
4
Combine
Earth clip (1)
5
Neutral U plate (1)
6
Neutral clip (1)
7
Include snap fit
Cover socket (1)
8
Switch on/off (1)
No Action
Switch on/off (1)
9
17
Spring (1)
No Action
Spring (1)
10
18
Panel 3 pin (1)
No Action
Panel 3 pin (1)
11
19
Screw φ5X12 (2)
Change to snap fit
20
Screw φ6X24 (2)
No Action
No Action
Combine
Screw φ6X24 (2)
Number of Unique Components
The new design gives a good result in terms of total number of unique
components. Referring to the results obtained, the original design which consists of 20
different types of components has been reduced to only 12 different types of components
in the new design implemented. This indicates that total of 8 components in types have
been eliminated with the reduction percentage of 40.0%. The improvements concentrate
on eliminating screw and changing it to snap fit and combining life, earth and neutral
12
112
components. To see more details on the action take on the old design, please refer to
Table 9.2.
9.4.3
Assembly Index for Product Level
The assembly index for product level of the original design is 77.8% meanwhile
for the new design is 87.3%. The difference in percentage of the assembly index for
product level is 9.5%. This contributes to an increase of 12.2% in the assembly index.
The increment has given a acceptable value for automatic assembly.
9.4.4
Assembly Index for Part Level
The assembly index for part level of the original design is 62.3% meanwhile for
the new design is 71.8%. The difference in percentage of the assembly index for product
level is 9.5%. This contributes to an increase of 15.2% in the assembly index. The
increment has given a acceptable value for automatic assembly. Part level index is more
critical in measuring the design performance compare to product level index. It is because
the part level evaluates every single components of the product regarding to all its design
rules.
113
CHAPTER 10
CONCLUSIONS AND FUTURE RECOMMENDATIONS
10.4
Introduction
After completing all the tasks required to fulfill the scope of project,
some important concluding remarks and future recommendations are discussed in this
last chapter.
10.5
Conclusions
The use of DFAA methodology for assembly analyses is to provide the best
product design in terms of reducing the part in a product. This will shorter the assembly
time, lower the manufacturing and assembly cost, besides increasing the quality of the
product. The main purpose of this project related to DFAA where the product design is
improved by determining the Assemblability Design Efficiencies (ADE) using Design for
Automatic Assemblies (DFAA) methodology for mechanical product. For this project,
the mechanical product is a 3 pin wall socket.
114
Achieving this purpose it requires four stages which must be accomplished
included:
1. First stage: The literature review is done on DFX, DFA and DFAA. In DFX, the
relationship ‘Design for’ methods under the same family of DFX is identidy. For
DFA methods, the well known ones such as Boothroyd-Dewhurst DFA Method,
Lucas-Hull DFA Method, and Hitachi Assemblability Evaluation Method
(AEM)is discussed. Lastly, more discussion is done on DFAA to get a clear view
on the concept.
2. Second stage: Identify the mechanical product for the project and did the ADE
which included the product detail, structure, sequence and the evaluation at
product level and part level.
3. Third stage: Redesign the product and proposed the new improvement which will
give a good impact to automatic assembly. The new design is done with its details
which included the product detail, structure, sequence and the evaluation at
product level and part level.
4. Fourth stage: Comparison between the old and new design is done to see if there
is any improvement on the product and gain the purpose of this project.
There are improvements in the new design where from ADE we can get the
differences between the old and new designs. The assembly index for product level has
an increment of 9.5% meanwhile for part level is 9.5% also. This has made the purpose
of this project where this product, 3 pin wall socket has improve the product design by
determining the Assemblability Design Efficiencies (ADE) using Design for Automatic
Assemblies (DFAA) methodology.
115
10.6
Future Recommendations
Possibly, there are some drawbacks existed in the current DFAA, and most of
them may be subjected for future research and improvement. For future
recommendations, there are a number of possibilities to be developed further on as stated
as below:
1. Introduce software that can simply the process of DFAA where the designer only
required to key in the necessary value to get the overall result. This will make this
methodology widely applied due to this simplicity.
2. The redesign process is a complicated process. It is a good helps to the designer if
software can be created to include all the design rules in part level and product
level of DFAA. Then, this software can integrate the information given by the old
product and make a new design with varies of optional which is suitable for the
design.
3. Automatic assembly can be done not only on the design area but also on others
areas such as machining, testing, production and etc. The application done and the
tool used should not be too complicated because it will burden the work done.
4. For part level, there is time estimation given but not implemented in the
evaluation. Therefore, the time estimation should be applied in the evaluation
later on so that user can compare the times needed for assembly between old and
new designs, and take this as an additional guide in improving product design.
116
REFERENCES
1. Eskilander, S. (2001). Design for Automatic Assembly- A Method For Product
Design: DFA2. Royal Institute of Technology, Stockholm: Doctoral Thesis.
2. Boothroyd, G., Dewhurst, P., and Knight, W. (1994). Product Design for
Manufacture and Assembly. New York: Marcel Dekker, Inc.
3. Boothroyd, G., Dewhurst, P. (1991). Product Design for Assembly. Boothroyd
Dewhusrt Inc.
4. Whitney, Daniel E., (2004), Mechanical Assemblies – Their Design, Manufacture,
and Role in Product Development, Oxford University Press
5. Crowson, Richard, Assembly Processes – Finishing, Packaging, and Automation,
Taylor & Francis Group.
6. University of Bolton. Design for eXcellence, Unit 1: Introduction to DFX. United
Kingdom.
http://www.ami.ac.uk/courses/ami4813_dfx/u01/s01/index.asp
Access Date: 16th February 2007
7. Design for X.
http://www.betterproductdesign.net/guide/design4X.htm
Access Date: 20th February 2007
117
8. Integrated Product Process Systems. Design for Assembly.
http://www.lboro.ac.uk
Access Date: 21st February 2007
9. WDK, Andreasen,M., M., Olesen, J., “Consensus Statemnets from DFX Workshop”,
Institute for Engineering Design, Denmark, 1993
118
APPENDIX A1
119
APPENDIX A2
120
APPENDIX B1
Design Samples of 3 Pin Wall Socket (Overall)