COST REDUCTION STUDY OF AUTOMOTIVE PART USING DFA M ETHOD...

COST REDUCTION STUDY OF AUTOMOTIVE PART USING DFA METHOD: CAR SEAT

MUHAMMAD BIN MOHD NOOR

Report submitted in fulfillment of the requirements for the awards of the degree of

Bachelor of Mechanical Engineering with Automotive Engineering

Faculty of Mechanical Engineering UNIVERSITI MALAYSIA PAHANG

JUNE 2012

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ABSTRACT

Design for Assembly (DFA) has been widely used in industry and has produced many

successes. Some of the methods known in the DFA industry now are the Boothroyd-

Dewhurst DFA method, Hitachi Assemblability Evaluation Method (AEM) and the

Lucas –Hull DFA method. With these well-known methods, many important changes

and developments carried out either manually or through the automatic assembly. The

goals of this project are to analyse existing car seat using Boothroyd-Dewhurst DFA

and Hitachi Assemblability Evaluation Method (AEM) in terms of assembly time,

assembly cost and assembly efficiency. The car seat that has been used in this project is

a car seat of Proton Wira. The original car seat has been analysed and showed that

Boothroyd-Dewhurst DFA has low percentage design efficiency compare to Hitachi

AEM DFA method. The assembly cost of both methods is same. The assembly time of

both methods also calculated.

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ABSTRAK

Reka bentuk untuk pemasangan (DFA) telah digunakan dengan meluas dalam industri

dan telah menghasilkan banyak kejayaan. Beberapa cara mengetahui dalam industri

DFA sekarang ialah kaedah Boothroyd-Dewhurst DFA, cara menganalisis Hitachi

Assemblability (AEM) dan kaedah Lucas DFA-Hull. Dengan kaedah-kaedah terkenal

ini, banyak pertukaran-pertukaran yang penting dan perkembangan-perkembangan

dijalankan sama ada secara manual atau melalui perhimpunan automatik. Matlamat-

matlamat projek ini akan menganalisis tempat duduk wujud menggunakan Boothroyd-

Dewhurst DFA and Hitachi Assemblability Evaluation Method (AEM) dalam soal masa

pemasangan, kecekapan kos pemasangan dan pemasangan. Tempat duduk yang telah

digunakan dalam projek ini ialah satu tempat duduk Proton Wira. Tempat duduk asal

telah dianalisis dan ditunjukkan yang Boothroyd-Dewhurst DFA mempunyai kecekapan

reka bentuk peratus rendah berbandingan kaedah Hitachi AEM DFA. Kos pemasangan

kedua-dua kaedah sama. Masa pemasangan kedua-dua kaedah turut dikira.

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TABLE OF CONTENTS

Page

EXAMINER APPROVAL DOCUMENT i

TITLE PAGE ii

SUPERVISOR’S DECLARATION iii

STUDENT’S DECLARATION iv

DEDICATION v

ACKNOWLEDGEMENTS vi

ABSTRACT vii

ABSTRAK viii

TABLE OF CONTENTS ix

LIST OF TABLES xii

LIST OF FIGURES xiii

LIST OF SYMBOLS xv

LIST OF ABBREVIATIONS xvi

CHAPTER 1 INTRODUCTION

1.1 Introduction 1

1.2 Problem Statement 3

1.3 Project Objectives 3

1.4 Scopes of Study 4

1.5 Expected Outcomes 4

1.6 Report Arrangement 5

CHAPTER 2 LITERATURE REVIEW

2.1 Introduction 6

2.2 Design for Assembly (DFA) 6

2.3 General Design Guidelines for Manual Assembly 7

2.3.1 Design Guidelines for Part Handling 8

2.3.2 Design Guidelines for Insertion and Fastening 9

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2.4 Design for Assembly Method 16

2.4.1 Boothroyd-Dewhurst DFA Method 16

2.4.2 Hitachi Assemblability Evaluation Method (AEM) 24

2.4.3 Lucas-Hull DFA Method 31

2.5 Comparison of DFA Method 34

2.6 Previous Research 40

2.7 Conclusion 43

CHAPTER 3 METHODOLOGY

3.1 Introduction 44

3.2 Design of Project Study 46

3.3 Disassemble and Measuring the Product 47

3.4 Drawing of the Product 48

3.5 Example of Manual Calculations of Boothroyd DFA Method 50

3.6 Example of Manual Calculations of Hitachi AEM DFA Method 52

3.7 Conclusion 53

CHAPTER 4 PRELIMINARY RESULT AND DISCUSSION

4.1 Introduction 54

4.2 Product Information 54

4.3 Product Design Analysis using Boothroyd-Dewhurst DFA 58

4.3.1 Original Design Analysis 63

4.3.2 Original Design Calculations 66

4.3.3 Redesign 1 Analysis 67

4.3.4 Redesign 1 Calculations 70





4.4 Product Design Analysis for Hitachi AEM DFA Method 79

4.4.1 Original Design Analysis 79

4.4.2 Original Design Calculations 84



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4.5 Summary 101

4.5.1 Results of Boothroyd DFA method 101

4.5.2 Results of Hitachi AEM DFA method 101

4.6 Conclusion 102

CHAPTER 5 CONCLUSIONS AND RECOMMENDATIONS

5.1 Introduction 103

5.2 Conclusion 103

5.3 Recommendations for Future Works 104

REFERENCES 105

APPENDICES

A1 Manual Handling 106

A2 Manual Insertion 107

B1 Gantt Chart FYP 1 108

B2 Gantt Chart FYP 2 109

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LIST OF TABLES

Table No. Title Page

2.1 Manual assembly worksheet for the original design 22

2.2 Manual assembly worksheet for redesign 1 23

2.3 Manual assembly worksheet for redesign 2 24

2.4 Hitachi AEM DFA method worksheet 28

2.5 Assemble of a pneumatic pump 30

2.6 DFA methods comparison table 34

2.7 Previous Research of Boothroyd DFA Method and Hitachi AEM

DFA method

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3.1 Table for computation of design efficiency 51

4.1 Reference specification of dimension and weight of Proton Wira 55

4.2 The main components of the car seat 58

4.3 Boothroyd DFA worksheet for original design analysis 65

4.4 Boothroyd DFA worksheet for redesign 1 analysis 69



4.7 Assembly process and operation of the original car seat 74

4.8 Hitachi AEM worksheet for original design analysis 83

4.9 Assembly process and operation of the redesign 1 car seat 86

4.10 Hitachi AEM worksheet for redesign 1 analysis 89





4.15 Results of Boothroyd DFA method 101

4.16 Results of Hitachi AEM DFA Method

101

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LIST OF FIGURES

Figure No. Title Page

2.1 Geometrical features affecting part handling 8

2.2 Geometrical features affecting part handling 8

2.3 Incorrect geometry can allow part to jam during insertion 11

2.4 Provision of air-relief passages to improve insertion into blind

holes

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2.5 Design for ease of insertion: assembly of long stepped bushing

into counter-bored hole

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2.6 Provision of chamfers to allow easy insertion 12

2.7 Standardize parts 13

2.8 Single-axis pyramid assembly 13

2.9 Provision of self-locating features to avoid holding down and

alignment

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2.10 Design to aid insertion 14

2.11 Common fastening methods 15

2.12 Insertion from opposite directions requires repositioning of

assembly

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2.13 Alpha and beta rotational symmetries for various parts 18

2.14 General rule for size and thickness 18

2.15 Selected manual insertion time standards, seconds 19

2.16 Original design 21

2.17 Redesign 1 22

2.18 Redesign 2 23

2.19 Hitachi’s AEM procedure 25

2.20 Direction of motion of a part 26

2.21 Fixture & forming requirements 27

2.22 Joining & processing requirements 27

2.23 Other symbols without penalty points 28

2.24 Assemble of a pneumatic pump 29

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2.25 Original drain pump assembly design 32

2.26 Redesign using the Lucas DFA method 33

3.1 Flow chart 45

3.2 Car seat drawing 48

3.3 Product tree of the car seat 49

3.4 Pneumatic piston sub-assembly 50

3.5 Assemble of a screw to a body 52

4.1 Location of car seat 55

4.2 Car seat Proton Wira 55

4.3 Product tree of the car seat 56

4.4 Redesign 1 67

4.5 Modification of back rest assembly

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4.6 Modification of bolts and nuts 68

4.7 Redesign 2 71

4.8 Modification of front back adjuster assembly 72

4.9 Redesign 3 76

4.10 Modification of pump assembly 76

4.11 Assembly sequences of the original car seat 80

4.12 Assembly sequences of the redesign 1 car seat 85

4.13 Assembly sequences of the redesign 2 car seat 91

4.14 Assembly Sequences of the redesign 3 Car Seat 96

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LIST OF SYMBOLS

Ema Design efficiency

Nmin Theoretical minimum number of parts

Ta Total assembly time

Tma Estimated time to complete the assembly of the product

E Assemblability evaluation score ratio

K Assembly cost ratio

α Rotational symmetry of a part about an axis perpendicular to its axis of

insertion

β Rotational symmetry of a part about its axis of insertion

T Time

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LIST OF ABBREVIATIONS

NM Theoretical Minimum Number of Parts

TM Total Assembly Time

DFA Design for Assembly

DFM Design for Manufacture

DFMA Design for Manufacture and Assembly

AEM Assemblability Evaluation Method

AOPDO Assembly-Oriented Product Design and Optimization

IDEFO Integration Definition for Function Modelling

CA Component Accessibility

PA Product Assemblability

SAS Spreadsheet Analysis

DFAA Design for Automatic Assemblies

ADE Assemblability Design Efficiency

FYP 1 Final Year Project 1

FYP2 Final Year Project 2

ASF Assembly Flow Flowchart

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CHAPTER 1

INTRODUCTION

1.1 INTRODUCTION

Seat comfort or discomfort evaluation is a key aspect in seat design.

Functionality of the seat can easily be evaluated through available state-of-the-art

technology solutions but comfort or discomfort and aesthetic factors are still very much

relying on human‟s perception. Although there are efforts on developing intelligent

systems, it still needs to be fed with information from human‟s subjective evaluations.

Human perception changes with time, hence updated information from new subjective

evaluations are always needed. Seat design procedure depends largely on the basic

mechanical aspect such as geometric parameters of seat, choice of suspension system

and cushion material used. However, the mechanical parameters can show certain data

in terms of seat design but how it affects the user is still unknown.

The comfortable, safety, legal and assembly of car seat is required by the

automotive industry which designer or engineer are needs to obtain an overall

understanding and know-how knowledge of vehicle requirement. The driving posture,

reachability, and vision are the area analysis in making the car seat. The driving

posture will evaluated for different population and evaluated the rate against a target

driving posture .The seat position was evaluated for each manikin for optimal posture.

To suit the need for comfort of driver and passenger, seat cushion with tilt adjuster can

be adopted to reduce the thigh pressure point. Steering adjustment is necessary to suit

varied occupant‟s shoulder height. Seat height adjustment will provide a suitable space

needed for varied occupant‟s leg length. The reachability is ability to reach controls

while in optimal driving posture. The reachability is in the plausible range since driver

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can move their seat forward to accommodate reach for steering and instrument panel.

Vision is the mirror where mannequin‟s field of vision can through room and the side

mirror.

The term “design for manufacture” (DFM) means the design for ease of

manufacture of the collection of parts that will form the product after assembly and

“design for assembly” (or DFA) means the design of the product for ease assembly.

Thus, the “design for manufacture and assembly” (DFMA) is a combination of DFA

and DFM. DFMA is used for three main activities. The first activity is used as the basis

for concurrent engineering studies to provide guidance to the design team in simplifying

the product structure, to reduce manufacturing and assembly costs, and to quantify the

improvements. The second activity, DFMA is used as a benchmarking tool to study

competitor‟s products and quantify manufacturing and assembly difficulties. Last but

not least of the third activity DFMA is used as a should-cost tool to help negotiate

supplier‟s contracts. (Boothroyd et al., 2002)

The automotive industry strongly encourages research in the field of cost

reduction of the car seat. Cost reduction is one of the most important issues to be

considered in automotive design. Therefore, study of DFA is used on the seat car in

order to reduce the cost and time of assembly by simplifying the product and process.

This project describes the cost reduction of car seat study by using DFA method. Focus

method of DFA on Boothroyd-Dewhurst (USA), Hitachi AEM (Japan) and Lucas (UK).

Current research and development efforts are described as well as areas for future

development and the projected impact on better performance of these seats in cost

reduction whereby focus on assembly efficiency, improved assembly operations and

benefits of the redesigned product.

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1.2 PROBLEM STATEMENT

Car seats are one of the most important components of vehicles and they are the

place where professional driver spend most of their time. Seating comfort is a major

concern for drivers and other members of the work force who are exposed to extended

periods of sitting and its associated side effects. In car seat manufactures, the product

car seat process has been assembled with the part component and fastener. There are

many problems part car seat to assemble, many parts to combine into one component,

some adjustment need to do in stabilize the car seat, there are also need to selected the

fastener for ease assembly, the long time in manufacture car seat and the manual

operation assemble is important to guide the car seat in the making. The costing of the

assembly is increasing by the problems stated.

This project is solving through the three method of DFA. The project aims to

minimize the difficulties encountered during assembly of the components of the car

seat. The improvements have been made in proposed design car seat to compare with

the existing of car seat design in term of cost assembly, assembly time and assembly

efficiency. Then, we should know the proposed design is improve or otherwise.

1.3 PROJECT OBJECTIVES

There are three objectives have been defined on this study by using DFA

methods are to:

(i) To analyze a product design for assembly efficiency.

(ii) To redesign the product for improved assembly operations.

(iii) To quantify the benefits of the redesigned product.

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1.4 SCOPES OF STUDY

The following scopes of the project are determined in order to achieve the

objectives of the project:

(i) The selected product has about twenty mechanical components.

(ii) The analysis of the original design and the improvement of the design of car seat

are performed by using Boothroyd-Dewhurst DFA method and Hitachi AEM

DFA method.

(iii) The original design and the improvements of the design are performed by using

Solidworks 2010 software.

(iv) The suggestions to reduce the assembly cost of the car seat are performed.

(v) The assembly cost of the original design and the improvements of the design of

the car seat is calculated and compared with the original design.

The project scopes done are the selected product has about twenty mechanical

components. The analysis is also done for original design and redesign of the existing

product that is car seat by using Boothroyd-Dewhurst worksheet and Hitachi AEM

worksheet of DFA method. The assembly cost of the original design of the car seat also

calculated.

1.5 EXPECTED OUTCOMES

At the end of this project Final Year Project 2, the design efficiency, total

assembly cost and total assembly time is calculated. Furthermore, there should have

minimum of 3 proposed alternatives of DFA method (Boothroyd-Dewhurst and Hitachi

AEM) and each of method was evaluated.

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1.6 REPORT ARRANGEMENT

This report is divided into five chapters. The chapter one is the introduction

about the project. It is includes the brief project, problem statement, project objectives,

scopes of the study and the expected outcome of the project.

The chapter two is discussed about literature review. This chapter provided with

introduction of the project design strategies and methods. In here, the general design

guidelines for manual assembly have been discussed. Then it also includes the brief

introduction to various methods of DFA, comparison of DFA method and previous

research method.

The chapter three is discussed about methodology of the project. Firstly the

design of project study and frame work is studied. Then it moves to disassemble and

measuring the product and drawing of the product of car seat. Furthermore, the manual

calculation of Boothroyd-Dewhurst DFA method and Hitachi AEM DFA method are

also been calculated.

The chapter four is focusing on preliminary results and discussion. The design

evaluation and Solidwork2010 software modelling are applied to the existing product

assembly. All the disassemble parts of the weight scale are critiqued and measured.

Then followed by manual calculation to lead time of assembly, estimated cost and

design efficiency. The results also have been analyzed.

The chapter five is about the conclusion and recommendations are made based

on the results that have gain in the research. This chapter also mentioned about the

alternative way to reduce the cost and increase the design efficiency by using DFMA.

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CHAPTER 2

LITERATURE REVIEW

2.1 INTRODUCTION

Design for Assembly (DFA) is measured by three of the better-known

quantitative evaluation techniques: Boothroyd-Dewhurst (USA), Lucas-Hull (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.

2.2 DESIGNS FOR ASSEMBLY

Design for Assembly (DFA) is define as an approach to reduce the cost and time

of assembly by simplifying the product and process through such means as:

(i) Reducing the number of parts.

(ii) Combining two or more parts into one.

(iii) Reducing or eliminating adjustments.

(iv) Simplifying assembly operations.

(v) Designing for parts handling.

(vi) Selecting fasteners for ease of assembly.

(vii) Minimizing parts tangling.

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(viii) Design a product for easy and economical production.

(ix) Incorporate product design early in the design phase.

(x) Improve quality and reduces the costs.

(xi) Shortens time to design and manufacture.

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." (Baizura, 2007)

The DFA analysis is first conducted leading to a simplification on the product

structure. Then early cost estimates for the parts are obtained for both the original

design and the new design in order to make trade-odd decision. (Rozie Nanie, 2004)

2.3 GENERAL DESIGN GUIDELINES FOR MANUAL ASSEMBLY

As a result of experience in applying DFA it has been possible to develop design

guidelines that attempt to consolidate manufacturing knowledge and present them to the

designer in the form of simple rules to be followed when creating a design.

The process of manual assembly divided into two separate areas, handling

(acquiring, orienting and moving the parts) and insertion and fastening (mating a part to

another part of group of parts).

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2.3.1 Design Guidelines for Part Handling

Figure 2.1 and 2.2 shows the design guidelines for part handling show product

design that is for manual assembly.

Figure 2.1: Geometrical features affecting part handling

Source: Boothroyd et al. (2002)

Figure 2.2: Geometrical features affecting part handling


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Figure 2.1 and 2.2 are also used for ease part of handling, whereas a designer

should attempt to:

(i) Design parts that have “end-to-end symmetry” and “rotational symmetry” about

the axis of insertion. If this cannot be achieved, try to design parts having the

maximum possible symmetry (see Figure 2.1a).

(ii) Design parts that, in those instances where the part cannot be made symmetry,

are obviously asymmetry (see Figure 2.1b).

(iii) Provide features that will prevent jamming of parts that tend to nest or stack

when stored in bulk (see Figure 2.1c).

(iv) Avoid features that will allow tangling of parts when parts stored in bulk (see

Figure 2.1d).

(v) Avoid parts that stick together or a slippery, delicate, flexible, very small, or

very large or that are hazardous to the handler (i.e. parts that are sharp, splinter

easily, etc.)(see Figure 2.2).

2.3.2 Design Guidelines for Insertion and Fastening

Figure 2.3 until Figure 2.12 are case for ease part of insertion, whereas a

designer should attempt to:

(i) Design so that there is a little or no resistance to insertion and provide chamfers

to guide insertion of two mating parts. Generous clearance should be provided,

but care must be taken to avoid clearances that will result in a tendency for parts

to jam or hang-up during insertion (see Figure 2.3-2.6).

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(ii) Standardize by using common parts, processes, and methods across all models

and even across product lines to permit the use of higher volume processes that

normally result in lower product cost (see Figure 2.7).

(iii) Use pyramid assembly that provide for progressive assembly about one axis of

reference. In general, it is best to assemble from above (see Figure 2.8)

(iv) Avoid, where possible, the necessity for holding parts down to maintain their

orientation during manipulation of the subassembly or during the placement of

another part (see Figure 2.9). If holding down is required, then try to design so

that the part is secured as soon as possible after it has been inserted.

(v) Design so that a part is located before it is released. A potential of problems

arises from a part being placed where, due to design constraints, it must be

released before it is positively located in the assembly. Under these

circumstances, reliance is placed on the trajectory of the part being sufficiently

repeatable to locate it consistently (see Figure 2.10).

(vi) When common mechanical fasteners are used the following sequence indicates

the relative cost of different fastening processes, listed in order of increasingly

manual assembly cost (see Figure 2.11).

(vii) Avoid the need to reposition the partially completed assembly in the fixture (see

Figure 2.12).

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Figure 2.3: Incorrect geometry can allow part to jam during insertion


Figure 2.4: Provision of air-relief passages to improve insertion into blind holes


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Figure 2.5: Design for ease of insertion: assembly of long stepped bushing into

counter-bored hole


Figure 2.6: Provision of chamfers to allow easy insertion


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Figure 2.7: Standardize parts


Figure 2.8: Single-axis pyramid assembly


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