Cost Reduction Study of Automotive Part Using Dfa Method: Car Seat
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 vii
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.
viii
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.
ix
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
x
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 4.3.5 Redesign 2 Analysis 71 4.3.6 Redesign 2 Calculations 74 4.3.7 Redesign 3 Analysis 75 4.3.8 Redesign 3 Calculations 78
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 4.4.3 Redesign 1 Analysis 85 4.4.4 Redesign 1 Calculations 90 xi
4.4.5 Redesign 2 Analysis 91 4.4.6 Redesign 2 Calculations 95 4.4.7 Redesign 3 Analysis 96 4.4.8 Redesign 3 Calculations 100
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
xii
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 40 DFA method 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 4.5 Boothroyd DFA worksheet for redesign 2 analysis 73 4.6 Boothroyd DFA worksheet for redesign 3 analysis 77 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 4.11 Assembly process and operation of the redesign 2 car seat 92 4.12 Hitachi AEM worksheet for redesign 2 analysis 94 4.13 Assembly process and operation of the redesign 3 car seat 97 4.14 Hitachi AEM worksheet for redesign 3 analysis 99 4.15 Results of Boothroyd DFA method 101 4.16 Results of Hitachi AEM DFA Method 101
xiii
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 11 holes 2.5 Design for ease of insertion: assembly of long stepped bushing 12 into counter-bored hole 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 14 alignment 2.10 Design to aid insertion 14 2.11 Common fastening methods 15 2.12 Insertion from opposite directions requires repositioning of 15 assembly 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 xiv
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 68
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
xv
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
xvi
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
1 4 4 4 4
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
2 4 4 4 4 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.
3 4 4 4 4 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.
4 4 4 4 4 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.
5 4 4 4 4 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.
6 4 4 4 4
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.
7 4 4 4 4 (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).
8 4 4 4 4 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
Source: Boothroyd et al. (2002)
9 4 4 4 4
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).
10 4 4 4 4 (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).
11 4 4 4 4
Figure 2.3: Incorrect geometry can allow part to jam during insertion
Source: Boothroyd et al. (2002)
Figure 2.4: Provision of air-relief passages to improve insertion into blind holes
Source: Boothroyd et al. (2002)
12 4 4 4 4
Figure 2.5: Design for ease of insertion: assembly of long stepped bushing into counter-bored hole
Source: Boothroyd et al. (2002)
Figure 2.6: Provision of chamfers to allow easy insertion
Source: Boothroyd et al. (2002)
13 4 4 4 4
Figure 2.7: Standardize parts
Source: Boothroyd et al. (2002)
Figure 2.8: Single-axis pyramid assembly
Source: Boothroyd et al. (2002)