A Framework for Modular Product Design based on
Design for ‘X’ Methodology
A thesis submitted to the
Graduate School
of the University of Cincinnati
in partial fulfillment of the
requirements for the degree of
Master of Science
in the School of Dynamic Systems
of the College of Engineering and Applied Science
2013
by Anoop Sreekumar
Bachelor of Technology (B.Tech.)
Amrita Viswa Vidyapeetham, Kerala, India, May 2010
Committee Chair: Dr. Anil Mital ABSTRACT
New products are routinely introduced in the expanding consumer market. In spite of incorporating many advanced technical features, only a few of these are financially successful. While competition, economic, and cultural, experience, and reputation factors are major influences in the success, or failure, of a product, a well-researched and efficient design distinguishes successful products from others. Product design and development, is a vastly researched topic and Design for
‘X’ (DFX) methodology is the basis for majority of product design procedures presently. Yet, there exist no framework for product design and development that can guide a designer through each design criterion, or ‘X’, in this methodology. Such a framework, if existed, would list out the design attributes and design factors for each of the design criterion.
This purpose of this work is to establish such a framework for designing products. It is intended for this framework to be interactive while guiding the designer through each factor that may be critical in design. The framework described here considers 8 different criteria, each broken into design factors and sub-factors. Each design criterion is discussed as a separate design module. The design factors in each module and their influences on product design have been discussed in separate sections. The inter-dependence of the design modules, design attributes, and design factors has been identified, establishing the need for a framework which can serve as the basis for a comprehensive database for all the ‘X’s’ in the DFX methodology.
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ACKNOWLEDGMENTS
Firstly, I would like to thank the University of Cincinnati for accepting me for my graduate degree and for the financial assistance provided during the course of my academic stay.
I would like to express my sincere gratitude towards Dr. Anil Mital, my academic advisor, for his invaluable advice, assistance, and encouragement to me during the course of my graduate degree.
He has always been available with his vast knowledge and experience, whenever I found obstacles in the advancement of my research. Without his guidance, I would not have been able to complete my work in a professional and timely manner.
I would also like to thank Dr. David Thompson and Dr. Kumar Vemaganti for taking time out of their busy schedules to serve as members of my defense committee.
I would also like to thank my colleague Vignesh Ravindran, who has been a source of great assistance to me with his suggestions during the course of this research.
Last, but not the least, I would like to thank my family and all my friends for their unwavering support and faith in me.
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TABLE OF CONTENTS
Abstract…………………………………………………………………………………………….i
Acknowledgment…………………………………………………………………….……………iii
Table of Contents…………………………………………………………………………………iv
List of Figures…………………………………………………………………….…...... ix
List of Tables………………………………………………….…………………….………….…xi
1. Introduction……...………………………………………………………………..……….1
1.1 New Product Design and Development……………………………………...……1
1.2 Importance of Product Design and Development…………………………………1
1.3 Design for ‘X’ and its incorporation…………………………………………….…3
1.4 Framework Description..………………………………………………………..…3
2. Literature Review………………………………………………………..…………...……5
2.1 Products: Classifications and Examples…………………………………..….……5
2.2 Stages of New Product Design and Development………………………...………7
2.3 Modularity in Product Design……………………………………………..………9
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2.4 Design for Manufacturing (DFM) and Design for X (DFX)….…………………..9
2.4.1 Design for Functionality...... 12
2.4.2 Design for Materials………………………………………....…………....13
2.4.3 Design for Assembly and Disassembly……………....…….….……….…14
2.4.4 Design for Maintenance…………………...……………………………...15
2.4.5 Design for Usability………………………………………………………16
2.4.6 Design for Reliability………………..….…..……………….…...…….…17
2.4.7 Design for Cost…………………………………………………………...17
2.4.8 Design for Environment…………………………………………………..18
2.4.9 Design for Quality……………………………………………....…….…..19
2.5 Limitations of the current research………………………………………….…….20
3. Objective and Methodology………………………...………………………….………...21
3.1 Objective of the research...... …………………………………………………...21
3.2 The Product Design Flower Diagram……………………………………………..21
3.3 Methodology: Design factor identification, classification and inter-dependence...23
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3.3.1 Methodology………………………………...…………...…………...…..23
3.3.2 Inter-module interdependence……………………………………………24
3.4 Relevancy of the research ………………………………………………………..24
4. Modules of the Framework…………………………………………...……...……...……26
4.1 Function-Information Module……………………………………………………26
4.2 Materials Module……………………………………………………...………….29
4.3 Assembly - Disassembly Module…………………………………………………31
4.3.1 Grasping Attribute…………………………………………………..……33
4.3.2 Motion Attribute……………………………………………………….…35
4.3.3 Orientation Attribute...... ……………………………………………35
4.3.4 Connection Attribute……………………………………………………..36
4.4 Maintenance Module……………………………………………………………..37
4.5 Usability Module……………………………………………………………....…41
4.5.1 User Aggregation Level…………………………………………..………43
4.5.2 Functionality Aggregation Level…………………………………………43
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4.5.3 Reliability Aggregation Level……………………………….…………....43
4.5.4 Maintainability Aggregation Level…………………………….…………43
4.5.5 Safety Aggregation Level…………………………...……………………44
4.6 Reliability Module………………………………………………………………..45
4.6.1 Mechanical Aggregation Level…………………………………………...46
4.6.2 Human Aggregation Level………………………………………………..47
4.6.3 Environmental Aggregation Level………………………………………..47
4.6.4 Maintainability Aggregation Level……………………………………….48
4.6.5 Contributory Aggregation Level………………………………………….48
4.7 Cost and Environment Module…………………………………………………...49
4.7.1 Design for Cost/Economy (Cost/Economy Module)...…………………...49
4.7.2 Assembly Costs…………………………………………………………..50
4.7.3 Disassembly Costs………………………………………………………..50
4.7.4 Maintenance Costs………………………………………………………..51
4.7.5 Form Cost Aggregation Level……………………………………………51
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4.7.6 Material Cost and Process Costs…………………………………….……51
4.7.7 Design for Environment: Environment Module……..……….…...…...…52
4.8 Design for Quality (Quality Module)..…………………………………………...56
4.8.1 Functionality Requirements for Quality………………………………….56
4.8.2 Usability Requirements for Quality………………………………………57
4.8.3 Reliability Requirements for Quality……………………………………..57
4.8.4 Maintainability Requirements for Quality………………………………..57
4.8.5 Material Requirements for Quality……………………………………….57
5. Conclusion…………...……………….…..………………………………………..…...... 58
6. Future Work...…………………………...………………………………………………..61
6.1 Development of an interactive designer aid system………………………………61
6.2 Role of framework in the interactive system……………………………………...61
6.3 Capturing functional knowledge: deriving information from the framework…....61
6.4 Interaction between modules in the system………………………...…………….69
6.5 Final Remarks………………………………………………………………….....70
7. References………………………………………………………………………...... 72
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LIST OF FIGURES
Figure 2.1 Product Categories and Examples…………………………………………6
Figure 3.1 The Product Design Flower Diagram…………………………………….22
Figure 3.2 Methodology for establishment of the framework and the interaction
between criteria, modules and design factors…………………………….25
Figure 4.1 Design factor breakdown of grasping attributes………………………….34
Figure 4.2 Design factors breakdown for the maintenance module…………………39
Figure 4.3 Aggregation levels and design factor classification in the Usability
Module……………………………………………………………………42
Figure 4.4 Aggregation levels and design factors in the Reliability Module………..46
Figure 4.5 Aggregation levels and design factor breakdown for the Cost/Economy
Module…………………………………………………………….……...50
Figure 4.6 Environmental concerns in design for environment……………………...54
Figure 5.1 (A) Product Design Framework with aggregation levels……………………..59
Figure 5.1 (B) Progression of the framework: Modules, Aggregation Levels, Design
Factors, Design Parameters and Interactive Questionnaire………………60
Figure 6.1 Captured functional knowledge of a standard component………...... …..62
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Figure 6.2 Sample product: Disassembly of a ball point pen…….………………...63
Figure 6.3 Extraction of shape attributes for the custom component………...……65
Figure 6.4 Extraction of performance attributes for the custom component.….…..66
Figure 6.5 Extraction of force-motion attributes for the custom component….…..67
Figure 6.6 Captured functional knowledge of standard and custom components....68
Figure 6.7 Menu driven questionnaire in the intreactive system……………….….69
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LIST OF TABLES
Table 2.1 Functions specific to three stages of product design and development……..7
Table 4.1 Design attributes and design factors in the Function-Information Module...28
Table 4.2 Design Factors affecting Material Selection………………………………..29
Table 4.3 Determinants in assembly/disassembly……………………………………..32
Table 4.4 Attributes and design factors in assembly/disassembly…………………….33
Table 4.5 Tool Factors………………………………………………………………...34
Table 4.6 Human Factors……………………………………………………………...34
Table 4.7 Design factor breakdown of motion attribute……………………………...35
Table 4.8 Classification of detachable connection features…………………………..36
Table 4.9 Elemental subtasks in maintenance………………………………………...38
Table 4.10 Design attributes to ensure efficient pre-maintenance stage……………….39
Table 4.11 Maintenance procedure and methods employed during in-maintenance…..40
Table 4.12 Design attributes and design factors in mechanical reliability……………..47
Table 4.13 Form Cost breakdown…………………………………………………… 51
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Table 4.14 EOL strategies and design considerations in design for environment……..52
Table 4.15 Determinants and aggregation levels in Quality Module…………………..55
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Chapter 1: Introduction
1.1 New Product Design and Development
New Product Design and Development is the process by which new products are designed and developed. A systematic approach of product design starts with conceptualization of an idea by designers and its evaluation in terms of risks of failure, economic impact (profitability), and social impact (acceptance). Design refers to the activities that deal with the physical entities such as color, style, appearance, material, function, and feel of a product, whereas development includes market research, identification of an opportunity to introduce a new product that appeals to the market, testing, evaluation, modification after the initial design process, and finally marketing of the product during and after the design process and the final launch [1]. It may be undertaken by an individual, an enterprise or a business. Although the broad prospect of design and development is the same for all products, these methods and their implementation vary greatly from one product to another.
1.2 Importance of New Product Design and Development
New product design and development is a complex process involving careful planning in bringing about coherence in different aspects in engineering, marketing, financing, and human involvement. A product is a tangible (perceived by sense), or intangible (service, experience, motivation, etc.) entity that is offered in exchange for financial benefits or for other tangible or intangible entities [2] . The intention of designing and developing a new product can either be profit, service, or both.
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"When the change outside is greater than the change inside, the end is near" - Peter Drucker
In the present world, there is a high level of competition between companies and individuals in every profitable, and sometimes, even non-profitable areas. Although new products bring about new economic and business opportunities for companies, they carry an inherent risk of failure.
Studies of new product failure rate have stated that out of 3000 raw ideas, 100 exploratory projects are undertaken. Of these, 10 well-developed projects materialize and 2 fully fledged products are launched; only one attains commercial success. These statistics have not changed substantially over the past 40 years [3]. The first comparative study of product success and failure, conducted in the United Kingdom by The Scientific Activity Predictor from Patterns of
Heuristic Origins (SAPPHO) in the 1970’s, concluded that product success was attributed to satisfaction of the user needs, efficient and effective marketing and publicity, efficiency of the design and development process, and expertise of the designer [4, 5]. The Conference Board study of new American products examined the failure of 114 products from 66 industrial firms, and concluded that the principal causes of product failure were poor market research, ineffective product marketing, poor understanding of competition, and inaccurate pricing [6, 7]. Studies on
Hungarian electronic products [8], West German products [9] and Finnish products [10] had similar conclusions. These studies also noted that products that could attract the market tend to be more successful than those counterparts that were technologically advanced. Further, constant monitoring and evaluation of product development process was essential for ensuring minimal resource allocation to project failures. All these findings exhibit the importance of product design and development research.
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1.3 Design for ‘X’ and its incorporation
The present day design engineering process is focused on the Design for Excellence or Design for ‘X’ (DFX) methodology. In this methodology, ‘X’ stands for a number of design goals such as ‘Functionality’, ‘Assembly and Disassembly’, ‘Usability’, ‘Reliability’, ‘Materials’, ‘Quality’, etc. The intended objective of this methodology is the incorporation of elements from all these design considerations concurrently, such that their inter-dependence is well defined and within the acceptable limit that will not hinder the overall success of the product [11-16]. It is desirable to integrate multiple design criteria in order to eliminate any conflict, and for the realization of better products and services. The implementation of DFX methodology requires substantial levels of effort during early design stage, but results in a more predictable product that conforms to the user or customer specifications and needs, with a well-defined coherence between the design goals and methods for manufacturing.
1.4 Framework Description
A conceptual framework is implemented in research to represent the possible courses of action an idea would develop and progress through. It attempts to interlink all aspects of a theory, and brings about coherence between the different paths of its progression. There are different kinds of conceptual frameworks, such as working hypothesis, descriptive categories, practical ideal types, operations research model, formal hypothesis, etc. [17, 18]. A framework may represent an exploratory or descriptive research, decision making, explanation, or prediction. It functions through a mode of inquiry: by defining a problem, identifying the need for a solution, a historical review of the problem, the development of a methodology, a collection of data, and an analysis
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to filter out relevant information from the obtained data. Every research idea being unique, the outline and course of progression of each framework will differ.
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Chapter 2: Literature Review
2.1 Products: Classification and Examples
The description of products by ISO 8402 [2] is given below:
“A product can be tangible (e.g., assemblies or processed materials) or intangible (e.g., knowledge or concepts), or a combination thereof. A product can be either intended (e.g., offering to customers) or unintended (e.g., pollutant or unwanted effects).”
A broader classification of the different types of products is given by Hubka and Eder [19] and is listed below:
1. Artistic Works
2. Consumer Durables
3. Bulk or continuous engineered products
4. Industry products
5. Industrial products
6. Industrial Equipment products
7. Special purpose equipment
8. Industrial plant
In the abovementioned list, the importance of appearance decreases and importance of design increases from top to bottom. This work is more based for consumer durables and engineered
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products, rather than products that are artistic, information or industry based. Figure 2.1 gives graphic illustrations of products that belong to each of the above categories.
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2.2 Stages of New Product Design and Development
New product design and development can be divided into three phases: Pre-Development,
Design and Testing and Post-Development [20]. Table 2.1 lists the functions specific to each stage.
Table 2.1. Functions specific to three stages of product design and development [20]
Product Design and Development
Conceptualization, Market and Technical Research, Pre - Development Business and Financial Analysis, etc.
Product Development, In-House and Consumer Testing, Design and Testing Test Market/ Sell and Trial Production, etc.
Pre - Commercialization Business Analysis, Post - Development Production Startup, Market Launch, Advertising, Follow Up Analysis, Extension of Support, etc.
Conceptualization or idea generation is the first step in the new product development process.
There are different methods for idea generation, such as brainstorming, focus groups, etc. Idea generation is more of a qualitative nature than a quantitative one. The ideas are screened for different aspects based on the consumer market and technical aspects, to test their feasibility. The ideas that are deemed to be unrealistic are dropped, and those which are attractive in a business and financial analysis are forwarded to the next stage in the process: design and testing.
The second stage and esp. the product development section of Table 2.1 is of major interest to designers, as this section decides the fate of the product. Majority of the modern day new product
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development process derives from an approach termed as modular product design, which concurrently integrates and optimizes multiple design goals that facilitate the necessary functioning of a product, and its success. This stage involves the realization of the products by the most feasible manufacturing processes. These processes are selected based on a number of factors: the functionality, usability and reliability requirements, manufacturability and materials, cost, environmental factors, quality requirements, etc. The newly developed products are tested for defects and quality requirements by the manufacturers, and sometimes, even by a section of the consumer market pre-selected for testing. If the product is within acceptable limits for its many desirable features, such as functionality, quality, usability, etc., it is forwarded to the post- development stage.
The post-development stage of new product design and development involves analyzing the design and testing stage to commence commercial production of the product. It is succeeded by launching it in the market, advertising to generate and sustain interest in the product, analyzing the product performance and consumer reviews, improving upon troublesome aspects, preparing historical data bases for future modifications, and providing repair or replacement services for the product and its parts.
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2.3 Modularity in Product Design
Modularity creates functional independence in products, and hence has been termed as the goal of design [21]. Life cycle modularity can be described as a relative property of a product based on the number of components and subassemblies [22]. A product may contain many numbers of modules, comprising many number of components related to each other in certain manners.
These modules interact with each other and bring about the basic functionality of the product.
While this definition of modularity applies to how a product could be broken up into simpler levels, there exist certain other design criteria that play a crucial role in its success. These characteristics can be described as other goals of design. A satisfactory design solution for these criteria is achieved in modular product design through a methodology termed as Design for ‘X’
(DFX).
2.4 Design for Manufacturing (DFM) and Design for ‘X’ (DFX)
Value Engineering and Productability Engineering are two concepts from which modern product design is derived. Value Engineering is concerned with the product function and the associated costs, and Productability Engineering links the products selling price with its specifications, manufacturing methods, tooling, work force, etc., and ensures that all these factors stay in equilibrium. The optimization of the principles derived from these two concepts bring about certain issues in design, such as compromising the manufacturability of a product, thus leading to high manufacturing costs and a decline in potential profit. Modifications to a faulty design after manufacturing can be very expensive. Hence it is important to integrate design with manufacturing considerations during the early design phase [23].
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Design for Manufacturability (DFM) is the process of designing a product or component with the ease of manufacturing as the final goal. The productability and fabrication of the component is a major factor in DFM. Materials, tolerances, shapes, features, etc. are some of the important factors in DFM. Bralla [12] developed many guidelines for the design for manufacturability of parts and components. These guidelines have been used extensively by the manufacturing industry to attain a better coherence between the design of products and their manufacturability.
Design for Excellence or Design for ‘X’ (DFX) is a much broader concept in which ‘design’ represents product design, and ‘X’ is a variable term which defines the design goal of any particular module in the DFX paradigm. Bralla [12] defines ‘X’ to be made of two parts: x
(design goal), and ability (performance measure). The incorporation of the performance measure is critical; the integration of multiple design criteria into a single product would produce conflicting decisions while attempting to perfect the product in each design criterion. Hence a balanced and acceptable equilibrium must exist between the design criteria, and this can be achieved by the introduction of the performance measure.
The nine dimensions of quality by Garvin [24] can be adapted as a good reference to derive the goals of product design. These dimensions are:
i. Performance
Performance reflects the primary characteristics of the product that would bring about its
functionality. Hence this dimension corresponds to the functionality of a product.
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ii. Features
Features are the characteristics of the product that contribute to its usability or handling.
Usability of a product as a design goal can be derived from this dimension.
iii. Reliability
Reliability of a product refers to the consistency in its performance, to the expected
norms and for an expected period of time. Hence it is an important design goal.
iv. Conformance
Conformance is the measure as to how well the product meets the specified and expected
standards. This dimension reaffirms the importance of reliability in design.
v. Durability
Durability is endurance of the product that yields utility from its performance during the
expected life cycle. Hence durability can be considered as the contributing factor for
maintainability and reliability as design goals.
vi. Service
Service, or maintainability feature, refer to the operations that have to be conducted to
ensure, maintain, and/or enhance the sustenance of the functionality, usability, reliability,
and quality features of the product throughout its life cycle.
vii. Response
Response is a usability and functionality feature, which invokes a reaction to/from the
customer/user. This can be considered as a usability design goal. viii. Aesthetics
Aesthetics refer to the aesthetic features of the product.
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ix. Perceived Quality (Reputation)
Reputation or perceived quality is the customer’s opinion on a company or its product’s
ability to fulfill his/her expectation. This forms the basis for quality as a design goal.
All in all, these 9 dimensions of quality form the base for all the conceptual modules of design in
DFX. These conceptual modules can be identified as Design for Functionality, Design for
Materials, Design for Assembly and Disassembly, Design for Maintenance, Design for Usability,
Design for Reliability, and Design for Quality. The importance of financial success, coupled with the increasing awareness towards environmental impacts of a product lead to another conceptual module, Design for Cost and Environment. There exist many other variations derived from these preliminary modules, such as Design against Corrosion, Design for Minimum Risk, Design for
Short Time to Market, Design for Standards, etc. These variations are specific to specialized designs.
2.4.1 Design for Functionality
The main objective of any product is to perform some function. This can be expanded by stating,
‘All product designs exist to satisfy certain intended function.’ Products that do not provide the intended function are set to be a certain failure. Even though functionality is a well-researched area in the field of product design, there exists no clear or uniformly accepted definition for it.
Function has been interpreted in a variety of methods; the traditional method of functionality representation in design has been the verb-noun method, where the function of a product would be explained in the form of a verb, and a noun {e.g.: Function of a shaft: transmit (verb) torque
(noun)}. Pahl et al. [25] presented a design methodology to determine the entire function of a
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product by analyzing its specifications. The function is recursively divided into sub functions.
For each sub function, a standard catalog is referred to identify the most appropriate functional element, component, or a set of components that could perform the intended sub function.
Finally, to perform the whole function, the designer has to choose from a set of solutions. The efficiency of this method depends upon how accurately and precisely the sub functions can be formulated. There also exist a variety of other functionality techniques, such as Value
Engineering System [26], Function Analysis System Technique (FAST) [27], Rodenacker’s
Methodology For Functional Representation [28], Sturges’s Extended Function Logic [29],
Concept Generation Algorithm [30], and Function Failure Design Method [31]. These extensive research works reaffirms the importance of functionality in design.
2.4.2 Design for Materials
Material selection in product design can be a very challenging task as it requires a profound understanding of the material properties that may or may not qualify a specific material for a specific component of a product. The level of difficulty ascends when the number of components increases with the product complexity. Compatibility of matching parts or components in a product has a direct relation to the compatibility of the materials used for their manufacture. The identification of materials at the early design stage is important for situations where the functionality is specific and directly related to the material, for designs which rely on material strength and properties, and where material solution is more important than a structural solution
[32]. There exists a variety of methods that can be employed to map the required function to a specific material: direct function–structure/material mapping, behavior-assisted function–
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structure/material mapping and behavioral process-assisted function–structure/material mapping, knowledge based material selection in design, and material selection using graph theory and matrix model [33-35]. These techniques attempt to simplify the task of the designer in the design for material based on other requirements of the product, such as functionality and usability.
2.4.3 Design for Assembly and Disassembly (DFA, DFDA)
Design for Assembly (DFA) is the design approach of analyzing the overall product structure to establish whether components can be added, deleted, or combined. It is used to improve the overall performance of the product during the long run, by bringing maintenance and reliability into consideration. DFA can save costs in the manufacturing phase by reducing the number of parts, thus saving significant portions of labor, material, overhead and testing costs. It is also expected of products with lower number of parts to have better quality [12]. DFA also ensures that products are put together in the correct sequence by using proper sets of jigs and fixtures, and by the proper usage of correct tools and manpower. The common DFA techniques that are used in modular product design include Boothroyd Dewhurst Method [36], Assembly Evaluation
Method [37], and an expert system to estimate the cost of part handling and assembly equipment for a two dimensional part design [38].
A very popular definition of disassembly is “the process of systematic removal of desirable constitute parts from an assembly while ensuring that there is no impairment of parts during the process” [39]. Disassembly can be categorized into two types, namely destructive and non- destructive. As the names suggest, destructive disassembly is more intended for recycling or disposal than non-destructive disassembly, which may be useful for maintenance or reuse.
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Design for Disassembly (DFDA) is important for the above said end-of life conditions (reuse, recycle) and maintenance operations, as it helps to establish a sequence of operations into the product design by which an assembled product can be broken down into its components or parts.
Two prominent techniques for DFDA include the disassembly sequence determination approach
[40] and a graph based heuristic approach for automatic disassembly sequence generation [41].
DFDA play an important role in modern day products unlike in the past, when products were designed just with assembly as a design goal and disposal was the primary end-of-life action.
This rise in the prominence of DFDA can be attributed to expected longevity in the functioning of a product which is brought about by maintenance operations, for which ease of disassembly is a crucial factor.
2.4.4 Design for Maintainability
Maintainability can be defined as “the degree of facility with which an equipment or system is capable of being retained in, or restored to serviceable operation. It is a function of parts accessibility, interval configuration, use and repair environment, and the time, tools and training required to effect maintenance” [42]. Design for Maintainability focuses on the maintenance of a product during its lifecycle to retain its functionality, usability, reliability and quality.
Maintenance operations can be of two types: preventive maintenance and corrective maintenance. Preventive maintenance can be described as the routine maintenance operations that are carried out to reduce the probability of failure of a product or component, while corrective maintenances are reactive in nature, and undertaken only when a specified component or a product fails and has to be restored to its previous working condition to recover its lost
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ability. Some well-known techniques to ensure the ease of maintainability in a product include the SAE maintainability method, the Bretby Index, the RCM Methodology and the Federal
Electric Method. [43]. Even with all the advantages these techniques offer, the fact is that they are reactive in nature and do not contribute directly to the design phase, but rather to the operating phase. Design for Maintainability in the modular product design corresponds to the allowances for maintenance which are included in the design phases. These allowances are incorporated into the assembly and disassembly features of a product.
2.4.5 Design for Usability
There is a high degree of importance for user-friendliness in modern day products, and this may be attributed to the development of electronics. Visual and sound controls and alerts are vital features of products in the 21st century due to the high level of interaction they facilitate between the user and the product, thus reducing the complexity of usage, and hence increasing usability.
This can be determined as the major reason as to why design for usability is important. Usability of a product can be described as the characteristics through which it meets certain expectations of the user during its life cycle. It can be also described as the response of the product to the needs of the user. Nielsen [44] named the five main usability characteristics as: learnability (the efficiency to retain the information that has been learned), familiarity (ability to repeat tasks that has been undertaken before without having to be trained again), forgiveness(allowances for mistakes by the user) and self-correction (for user errors) and finally the satisfaction of the user[44]. The main targets to be achieved by design for usability are: simplification of the product structure to ease the user difficulty, the easy and effective achievement of functionality,
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the provision to provide feedback for performance index and future use and to prevent, or correct user errors.
2.4.6 Design for Reliability (DFR)
Reliability can be described as the probability that a product will satisfactorily perform its intended function, under certain operation conditions and for specified operating conditions.
Product reliability is an important phase of design, as poor reliability result in frequent product failure, greater repairing and warranty costs, customer dissatisfaction, decline in sales, and overall business failure. Design for Reliability focuses on improving the overall reliability of a product concurrently with the improvement in design, manufacturing, material selection and quality [45]. Many standards are used measure the reliability of a product, such as Mean Time to
Failure (MTTF), Failures per billion operating hours (FITS) etc. Another methodology termed
Reliability Growth Test can be used as a testing method for product reliability assurance [46].
With the advent of computers modern day reliability testing, quantification and validation during product development and growth phase is done by knowledge based decision support system
(DSS) [47]. Reliability can make or break the long term future of a product; hence Design for
Reliability is an important goal of product design during its early phase.
2.4.7 Design for Cost
Past research has stated that the major portion of cost committed for a product is at its early design stage, estimated at 70% [48]. This underlines the importance of designing for cost during the design stage of any product that expects a financial return (i.e. profit). Cost estimation is also important as it helps a designer to plan ahead for all the costs that may incur during a set of
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activities, and in turn to select those set of activities that are feasible, both process-wise and economically. Many cost prediction and modeling systems have been developed with the importance of cost estimation in mind. Shehab and Abdalla [49] developed a prototype that not only predicted the material and processing costs at the early design stage, but also took into account the non-productive costs and set-up costs. Wei and Egbelu [50] developed a framework which estimated the cost for manufacturing from the geometric design of the part. An AND/OR tree was developed in this framework, and this tree helped in the decisions which yielded the lowest manufacturing cost for thorough the development of alternate processes. Gayretli and
Abdalla [51] developed a system using mathematical models and constraint programming techniques, which allowed the designer to optimize the processes that were feasible in the manufacturing of a product. Cost models has also been developed for specific products, such as gear drives [52], and for processes, such as injection molding [53] in mind. These models understand and assert the importance of incorporating cost management and control into an early design phase, making design for cost an important goal in product design.
2.4.8 Design for Environment (DFE)
The preservation of environment has become a major issue in the 21st century. Pollution level, air and water alike, has caused dramatic changes in climate, ecological life, and human population.
The increasing concern towards future generations, the depletion of natural resources have resulted in an increase in the awareness towards the need of preservation of the environment, and the reduction in contamination levels. This has led to the green movement, aimed at the inclusion of environmental friendliness in our day-to-day lives. This trend has caught on in product design,
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with the advocacy of green design or Design for Environment [12, 54], an approach in which a designer opts for design guidelines and manufacturing methods that are environment friendly.
These guidelines have been covered extensively by Bralla [12] and Ashley [54], with importance given to the waste disposal, recycle-reuse-remanufacture methods, substitutional eco-friendly materials, avoidance of emissive gasses, etc. The end-of-life factors in disassembly are also related to design for environment, with recycling and remanufacturing gaining precedence over disposal. The avoidance of toxic materials, such as Chloro - Fluro Carbons, Benzamine, etc. are a result of the increased awareness towards green manufacturing and design for environment.
2.4.9 Design for Quality (DFQ)
The quality expectations of a product are very high in the consumer market. Quality is an important measuring tool which provides a company a competitive advantage in the market.
Radford [55] describes quality in engineering and industry to be a single or group of characteristics that distinguish the services or products of one manufacturer from that of its competitors. Garvin [24] described the nine dimension of quality that a product should possess for its success. He also asserted the importance of cross functional product development teams in total quality management of products. Perceived quality or reputation is very important to a product’s success. Quality is dependent on a number of other design goals, such as functionality, reliability, safety, usability, etc. Inspection and maintenance plays an important role in ensuring the continued quality levels of a product. The incorporation of quality measures, such as six sigma, corrective and preventive action, first article inspection, etc. is widely done in the
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manufacturing industry, with a lot of emphasis on reducing the number of defective products or parts.
2.5 Limitations of the current research
Although a significant amount of research has been conducted in the many goals of modular product design, these have been in the study and development of various techniques that may be implemented in a certain design criteria. There is no single methodology that breaks down the requirements for each of these criteria into design attributes and design factors that need to be considered in the actual product design.
This work aims to develop a framework for product design by establishing inter-functional dependence of the design elements for each criterion of product design for engineered products.
It should be noted that the incorporation of multiple design criteria does not mean the highest level of optimization of all element with respect to any one criterion, but selection of the best possible compromise for all the design factors that is within the acceptable limits so that the effectiveness of other design goals does not suffer when design for a particular X is done.
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Chapter 3: Objective and Methodology
3.1 Objective of the research
The overall objective of this work was to create a framework for an interactive modular system to assist designers improve product design. This framework is intended to guide a designer through different criteria of product design based on the DFX methodology. The interactive modular system is expected to operate as a part of existing CAD packages and help improve the conceptual design of the designer based on the DFX principles. The subsequent sections will explain the framework in detail.
3.2 The Product Design Flower Diagram
The Product Design Flower Diagram (Figure 3.1) forms the base of the framework. The diagram consists of different modules of the product design framework, each module corresponding to a specific design criterion of product design. As one progress through the framework, design attributes and design factors for all these modules will be identified and integrated on to the diagram. Certain design attributes and design factors are inter-dependent, and may appear in multiple modules. An extended diagram will be depicted in the end, with all the design attributes pertaining to each module incorporated into the diagram. A mapping chart diagram of all the design attributes to design factors will be formed. This mapping chart is expected to show how the framework will be converted to the interactive system for product design in the future.
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3.3 Methodology: Design factor identification, classification and interdependence
3.3.1 Methodology
In the DFX paradigm, ‘X’ stands for different design criteria or goals, such as functionality, quality, reliability, etc. The proposed framework is divided into 8 separate modules, each corresponding to a particular ‘X’ in the DFX methodology. These modules are further broken down into a list of design attributes, design factors and their specifications are identified. These design factors will be used in the future to collect design specific information from both designer interaction and the actual CAD model. The list of design factors is not exhaustive, and each module has provisions to expand this list and add more design factors based on specific requirements. Design factors corresponding to design attributes are explained in detail in each corresponding module. Each design module will draw information from a base module termed the Function-Information module, and also from one another, depending on the response of the designer to an interactive questionnaire. An example is shown towards the end to demonstrate how the information is captured, and how the modules draw information from each other. Due to the complexity of this method, only the base module has been developed to the interactive system. The material module will be considered to show how the information is passed and the choices will be made based on the input by the designer.
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3.3.2 Inter-module interdependence
A designer improving his design solely on the basis of a particular design criterion is most likely to fail. Hence it is important to understand the relationship between different modules, and establish to how they interact with each other in the system to guide the designer efficiently.
Since the modules are not exclusive, some of the design factors will appear in different modules, indicating a link between these modules. Figure 3.2 depicts the structure of the framework and the inter-relationship between different modules.
When the later modules in the framework are considered, it is observed that the inter-dependence of the design attributes and the design factors increases.
3.4 Relevancy of the research
This research is expected to be the first step towards an intelligent and interactive system that can be attached to an existing CAD package. This system would guide a designer towards creating or modifying a product model by providing design solutions for the different design goals, eliminating conflicts among the different design criteria, and offering the best possible balance between all these criteria, according to the designer specification. Although there exists modules in certain CAD packages that can extract features from parts, and display the part-feature compatibility, all these modules function to attain better manufacturability. The proposed system will be more from a design perspective, by considering the design goals which affects a product as a whole.
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Chapter 4: Modules of the framework
4.1 Function-Information Module
Function is an abstract concept that depends on a number of varied and complex factors. The
Function-Information module in the framework identifies the designer as the link between the design and its intended function, in that it differs from other functional representation techniques.
The Function-Information module seeks specific inputs from the designer regarding his CAD design, and stores this information as a source for interpreting the function of the design. Though this information database is not comprehensive by any means, and does not define the product function in its entirety, it still acts as an effective checklist or constraint as specified by the designer to preserve the functional intent of the design. As the designer is guided through the other modules, this input information is to be used as a basis of the recommendations to be provided based on the checklist, and the designer will be flagged in case of potential conflicts.
As an example, it is assumed that the designer inputs high material density as a necessary functional requirement. As the system guides the designer through the cost module, if the designer chooses a low density material in order to minimize cost, the Function-Information module, which has the previously stored designer input regarding the material density, will immediately flag the functional conflict bringing it to the designer’s notice.
Each module in the framework will operate either at product level, or at intermediary assembly level, or at component level based on its relative relevance. Function-Information module, for
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example, will operate predominantly at the component level. Components are classified into two groups: standard or custom.
For standard components such as shafts, gears, chains, belts, etc., the Function-Information module understands their function, and will contain provisions to obtain efficient component specific information from the designer and the CAD. For custom components, the functional conformance of products is extracted, based on three primary attributes: shape, performance and force-motion attributes.
Shape attributes include the geometry, features, and finishing of the component. Performance attributes are the functionality features that affect the performance of the component.
Performance attributes can be further classified into material properties, usability features, quality features, reliability features, safety features, aesthetics, etc. The force-motion attributes deal with individual component movement, component–component interactions and the various loads and forces the components are subject to in a product.
The Function-Information module also has provisions to include other necessary miscellaneous attributes that cannot be classified under any of the primary attributes but contribute significantly to component functionality. Table 4.1 is a generic list of the three design attributes in the
Function-Information module. These attributes have been broken down into design factors.
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Table 4.1. Design attributes and design factors in the Function-Information Module
Design Criteria: Functionality
Design Attributes Design Factors
Shape Geometry, Features, Finishing, etc.
Acoustic, Chemical, Environmental, Magnetic, Manufacturing, Material Mechanical, Optical, Radiological, Thermal, etc.
Reliability Redundancy, Safety Factor, Material strength, Wear out, Testability
Performance Response Time, Customer Interface, Error rate, Simplicity, Usability Acclimatization time, etc.
Safety guards, Interlocks, Rounding, Surface finish, Material, Safety Safety factor, etc.
Surface finish, Material, Manufacturing process, Quality Testability, etc.
Forces: Fundamental (Linear, Rotational), Force and Motion Non Fundamental Motion: Rotational, Linear, Rolling, Harmonic, Oscillating, etc.
How the function-information module captures information from the designer based on an interactive questionnaire and the information is passed onto other modules is explained in
Chapter 6.
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4.2 Material Module
Material selection plays a major role in realizing the functional aspects of a product. A good material must provide optimum properties required by the product economically. Costs associated with material selection include not just the cost of material, but the cost of its availability, manufacturability, maintainability, serviceability, usability, disposability and environment compatibility. The concept of ‘Design for Material’ aims at improving the design to take complete advantage of all the features of material discussed above. The ‘Material Module’ in our system is the second module and is aimed at addressing the ‘Design for Material’ aspect in the DFX methodology. The Material module works in conjunction with all other modules including Function Information module and Cost module. Table 4.2 is a generic list of design attributes and factors that affect material selection. Material module operates predominantly at the component level.
Table 4.2 Design Factors affecting Material Selection
Material Selection
Design Attributes Design Factors
Physical Size, Shape, Weight etc.
Mechanical Stress, Impact Strength, Material properties etc.
Castability, Weldability, Hardenability, Formability, Production Process and Fabrication Rate etc.
Life of component Oxidation, Corrosion, Wear resistance, Creep etc.
Cost and Availability Production Quantity, Availability, Standardization etc.
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The primary objective of the material module is to ensure that the designer makes the right choice of material that fits the functional profile of the product. In order to achieve this, the material module will closely interact with various input attributes obtained from the designer and stored in the function information module discussed before. Based on this information, it will then eliminate a long list of materials and material families that do not match the functional requirements of the component and present the designer with a list of materials which fulfill the functional requirements. Material module will also consider inputs, such as geographic location of the manufacturing plant, in-house manufacturing process availability, and dynamic material vendor information, to present an economically feasible list of materials for the designer to choose from.
Once a material choice is made, the material module will then suggest to the designer to modify specific aspects of the design to accommodate the material-process choice made by the designer.
The material module will make use of an extensive database which includes details of all materials, material properties and make design recommendations based on material and process specific design rules.
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4.3 Assembly-Disassembly Module
Most products today are made of multiple components or parts. For example, a standard bike is made up of more than 200 parts, an automobile of nearly 30,000, and a Boeing 747 aircraft in excess of 6 million. If individual components are not designed for the ease of assembly, manufacturing and assembly become an expensive and time consuming process. The same factors apply to disassembly and maintenance when disposal, recycling, and repairs are taken into account. Hence design for assembly (DFA), design for disassembly (DFDA), and design for maintainability (DFM) are important aspects of product design.
Design for Assembly is a process in which products, or components, are designed with ease of assembly in mind. Any product that is equipped with fewer parts, and these parts in turn equipped with features that make them easier to grasp, move, orient or connect/insert with each other would take less time to assemble and thus, reduce the assembly costs. There are three basic types of assembly processes. Assembly process which involves manual operations with or without the aid of simple tools is known as manual assembly. Automatic assembly involves the use of machines and is generally implemented with a single product in mind. Robotic assembly, or soft automation, is a type of assembly process that incorporates the use of robotic assembly systems (single or multi-station robotic assembly cells). There are a variety of reasons for disassembling products. They could be disassembled completely for disposal, or partially and selectively for maintenance operations or replacement of parts. A product and its components are better suited for re-use or recycling at the end of life if design for disassembly is taken into
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consideration during the development stage. This eliminates the need for new products and in turn brings about a better return on the investment by the user.
Assembly and disassembly being reverse operations in nature; the design factors for both operations have been identified and classified into the same category to ensure uniformity of information in the design process.
The determinants in an assembly/disassembly procedure can be divided into three sections: ends, means, and processes. The description of these determinants and the broad categories that design factors fall into in each of these determinants are listed in Table 4.3.
Table 4.3 Determinants in assembly/disassembly
Determinants Design Attributes
Ends Material, Parts, Subassemblies
Means Tools, Fixtures, Others
Processes Motion of parts, Sequence, Operating Conditions, Operator Efficiency
The design factors for assembly and disassembly are categorized into four attributes: grasping, motion, orientation, and connection, as shown in table 4.4. These are introduced to categorize design factors in the assembly/disassembly module under each specific and progressive stage of product development from the initial physical factors that influence the basic features of the product, such as strength and reliability, to the finished product that has to be assembled or disassembled.
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Table 4.4 Attributes and design factors in assembly/disassembly
Design Attribute Design Factors
Grasping Forces (Combination or Separation), Tool Factors, Human Factors
Motion Contact Condition, Interference, Spatial Arrangements
Orientation Weight, Geometry, Forces
Connection Fastening, Material, Joining Points
4.3.1 Grasping Attributes
The grasping attributes include features from the end determinant and the means determinant.
These attributes contain the forces necessary to join (assembly force) or separate (disassembly force) components of a product, the tool factors, and human factors that are necessary to facilitate the connection of components. A breakdown of the grasping attributes is given in figure
4.1.
It should be noted that the human factors are taken into account with manual assembly/disassembly in mind. Although many design factors belonging to these attributes may be applicable to automatic or robotic assembly or disassembly processes, the complexity involving these processes limits the scope of the assembly/disassembly module for manual operations. Tables 4.5 and 4.6 expand the design attributes of the tool and human factors, respectively.
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Table 4.5. Tool Factors
Design Attribute Design Factors
Tool Handling Level of accuracy, Access, Symmetry of the part, Human factors
Grip Power grip (tool, machine), Non – power grip (human)
Table 4.6. Human Factors
Design Attribute Design Factors
Access Visibility, Direction, Location of parts / joining point
Posture Gripping, Level of effort / exertion Hazard Protection None, Safety Accessories
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4.3.2 Motion Attributes
Motion attributes are derived from the process determinant, and are related to the motion of parts within the product structure, interference to such motions, and the spatial arrangement within the structure. Motions, restricted or unrestricted, play a key part in the ease of assembly, disassembly, and maintainability of a product. The spatial arrangements of the parts and the clearances that restrict or enable these motions also are essential for the same. These are listed in table 4.7.
Table 4.7. Design factor breakdown of motion attribute
Design Attribute Design Factors
Contact Condition Forces, Center of gravity, fastening methods, weight, geometry
Interference Spatial arrangement, clearances, geometry, weight
Usability requirements (product specific), Spatial arrangement, Clearances geometry, weight
4.3.3 Orientation Attribute
The orientation attribute is related to how the components are put together in a product, i.e., the sequence of assembly or disassembly that requires the least amount of time for these operations.
These are required to facilitate ease of disassembly and maintenance. Geometry, weight, and forces or assembly/disassembly play a major role in this attribute. Being product specific, it is difficult to generalize the functionality and usability features of this attribute.
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4.3.4 Connection Attribute
How parts are connected within a product structure is an important aspect of any assembly or disassembly operation. These attributes are the ones which define the assembly or disassembly process as they are pivotal in joining components together to complete the product structure.
Connections can be termed as fixed or detachable. Fixed connections are connections where two mating parts are permanently connected, such as in welding or soldering. These are suitable when a product has low cost and a short life time, and the end of life objective is disposal.
Detachable connections are the connections which can separate parts within a product structure at will for maintenance or replacement purposes. These are suitable for products that are expected to have a long life and reuse or replacements of parts are viable options. These connections generally are termed as fasteners. Detachable connections require proper interlocking methods, and fasteners that support the materials and geometry of the components and the product. A classification of the detachable connection features is given in table 4.8
Table 4.8. Classification of detachable connection features
Design Attribute Selection Criteria
Separate or integral fasteners – must support material, Fasteners force of assembly (shear, tension or compression), weight
Material Product Specific – depends on functionality, usability, etc.
Interlocking Method Force of assembly, material support, fastener support
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4.4 Maintenance Module
A system is said to be maintainable when a failure to perform as required by it can be corrected by a suitable methodology, be it repair or replacement [56]. A standard definition would be that given by the US Department of Defense which defines maintainability to be “a characteristic of design and installation which is expressed as the probability that an item will conform to specified conditions within a given period of time when maintenance action is performed in accordance with prescribed procedures and resources” [57]. Individual components of a product assembly will eventually damage and break down due to fatigue, wear and improper handling, and usage. A commercial product that cannot be maintained or returned to usable condition within reasonable time duration and cost limit will not survive in a competitive market and hence design for maintenance is an important aspect in product design.
As mentioned in section 2.4.4, maintenance tasks can be divided into two categories: preventive/predictive maintenance and corrective maintenance. Due to the nature of preventive or predictive maintenance where routine maintenance activities are conducted with the whole equipment failure in mind rather than a localized issue, the design factors listed in this module are more applicable to corrective maintenance.
The three determinants to classify the design factors affecting maintenance operations have been derived from the Federal Electric Method [57]. These determinants are termed as pre- maintenance, in-maintenance, and post-maintenance operations. The classification of design factors that are applicable to all the determinants has been derived from functionality and
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assembly/disassembly sections. These, along with the factors specific to maintenance operations have been listed in have been listed in table 4.9 and figure 4.2.
Table 4.9 Elemental subtasks in maintenance [57]
Determinants Maintenance Tasks
Localization and Isolation, Pre-inspection, Disassembly, Pre-Maintenance Preparation and cleaning
In- Maintenance Maintenance Operations
Post-Maintenance Reassembly, Post-inspection
The specific processes during the pre-maintenance and in-maintenance stage vary on a product- to-product basis. However, there exist certain common processes that are part of every maintenance operation. These processes have been adapted from Desai and Mital [43] and the design factors that are relevant during the employment of these processes are listed in tables 4.10 and 4.11. The post-maintenance operations include assembly, post inspection, and disposal and/or recycling of the waste. Post-inspection is a much easier process than pre-inspection due to the faulty component being isolated during the pre-inspection process.
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Table 4.10. Design attributes to ensure efficient pre-maintenance stage
Design Attribute Design Functions Design factors
Mechanical Cleaning Preparation/Cleansing Machine Cleaning Material Property, Hazards Liquid Cleaning
Disassembly Design factors from disassembly module
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Table 4.11. Maintenance procedure and methods employed during in-maintenance
Process Factors
Cleaning Material Properties, Human Factors
Lubrication Friction, Surface Roughness, Interference, Motion
Machining Surface Roughness, Weight, Material Properties, Geometry
Replacement Tool Factors, Human Factors
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4.5 Usability Module
The ISO 9241-11 Guidance on Usability [58] defines usability as “the extent to which a product can be used by specified users to achieve specified goals with effectiveness, efficiency, and satisfaction in a specified context of use”. In every successful product, there is a high degree of user interaction which may be physical, cognitive or both. It is important to have a simple yet appealing usability interface between the consumer and the product. Different products that are conceptualized with the same functionality in mind will not be equally successful and this can be attributed to the usability, reliability, and cost features of the products. Also, a technologically sophisticated product with complex usability features may not appeal to the masses as its counterpart which may be less advanced technically and yet more user-friendly. Hence, usability of a product is an important criterion in product design. The design factors to ensure usability of a product can be categorized into five determinants: user, functionality, reliability, safety, and maintainability. The design factors breakdown in these determinants and their derivation are represented in figure 4.3.
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4.5.1 User Aggregation Level
The user aggregation level comprises of design factors that make a product more attractive from users’ point of view. These can be further divided into safety features, human factors, aesthetic features, reliability features, and maintainability features. Aesthetic features can be further divided into product specific features, shape features, and surface features.
4.5.2 Functionality Aggregation Level
The functionality aggregation level classifies the functionality design factors that affect the usability of the product. These factors include the shape, performance, and force-motion factors mentioned in the Function-Information module.
4.5.3 Reliability Aggregation Levels
The reliability aggregation level refers to the design features and factors of a product that ensure its usability and functionality. The design factors in this level can be derived from the material properties (Material Module), functionality requirements (Function-Information Module), and the human factors (Table 4.6, Assembly–Disassembly Module).
4.5.4 Maintainability Aggregation Level
The level of maintainability of a product affects its usability, functionality, and reliability. The usability and functionality of a product declines over time and it is essential from the stand point of product success that a high level of maintainability exist to restore the usability of the product or the component.
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4.5.5 Safety Aggregation Level
The absence of undesirable events during the life cycle and operation of a product is termed as safety. This is an important criterion in product design as the demand for a product that has been deemed unsafe will decline and product recall is a very expensive and time consuming process.
Further, it damages the reputation of the manufacturer. The major areas that affect product safety include material properties (Material Module), human factors (Assembly-Disassembly module), forces on the products, motion of the components (Function-Information Module), etc.
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4.6 Reliability Module
Reliability can be described as the probability that a product will satisfactorily perform its intended function under certain operation conditions for specified operating conditions. Product reliability is an important phase of design as poor reliability results in frequent product failure, greater repairing and warranty costs, customer dissatisfaction, sales, and overall business failure.
The factors that facilitate the need for product reliability are product complexity, user specified clauses, market competition, designer or company reputation, cost effectiveness, and history of system failures. These factors in turn lead to the different stages of design for reliability, such as definition of the failure criterion, identification of the acceptable limits, analyzing the past system failures, quantification and improvement of the reliability factor within the acceptable limits, validation of the reliability factor of the product and monitoring, and control of this factor.
The reliability module in the framework consists of design factors categorized into 5 aggregation levels: mechanical aggregation level, human aggregation level, maintainability aggregation level, environmental aggregation level, and contributory aggregation level. The breakdown of these aggregation levels is given in figure 4.4.
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4.6.1 Mechanical Aggregation Level
Any tangible product consists of mechanical components and systems (electrical, hydraulic, etc.). These mechanical components may be fixed or movable according to their intended function. With these mechanical components come many mechanical factors that affect their functioning. These mechanical factors that affect the reliability of the product are categorized
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under mechanical aggregation level. Table 4.12 lists the breakdown and classification of these factors.
Table 4.12. Design attributes and design factors in mechanical reliability
Mechanical Reliability
Design Attributes Design Factors
Material Material properties – listed in functionality module
Surface Interference, Clearances
Force - Load External and internal forces, handling
Geometry Shape, size, weight, tolerances
4.6.2 Human Aggregation Level
The human aggregation level consists of the human factors that have been listed in the earlier modules. These can be categorized into operating errors, maintenance errors and inspection errors. These depend on the operator skill level.
4.6.3 Environmental Aggregation Level
The environmental aggregation level consists of the environmental factors that affect the reliability of a product. The major effects that an environment could exert on a product that could alter its reliability would be pressure and temperature changes, humidity and toxicity, vibration and interference, radiation, and magnetism. The type of environment which a product is to be functioning under is important in design. The environmental aggregation level contributes to the
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material module, where a selection or elimination of material will be made based on factors such as reactivity, corrosivity, toxicity, etc.
4.6.4 Maintainability Aggregation Level
As in usability, maintainability plays an important role in restoring the reliability of a product. A product has a certain life time during which the reliability decreases. The maintenance operations performed can restore the reliability of a product to a satisfactory level. The Maintenance
Module (section 4.4) covers the maintenance operations and the associated design factors.
4.6.5 Contributory Aggregation Level
Contributory aggregation levels include the product specific and other uncategorized attributes that a product must possess for it to be reliable. These factors contribute to the information part in the Function-Information Module.
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4.7 Cost/Economy Module and Environment Module
In the design for cost and environment module, the aggregation levels associated with the developmental costs and environmental impacts on product design are discussed in two separate sections.
4.7.1 Design for Cost/Economy (Cost/Economy Module)
Product Design has a large influence on manufacturing cost. To keep the selling price competitive, it is necessary to reduce the manufacturing cost to the lowest possible level. Studies have indicated that early stage of design can account for 70 % of the total cost associated with a product, while the actual design process accounts for only 6 % [48]. Hence the cost related decisions during the design have a much significant impact than the actual manufacturing cost of the product. This showcases the importance of designing for cost effectiveness in the product design framework. The cost/economy module in the framework categorizes the generic costs inquired during a design phase. The aggregation levels for the cost/economy module can be broadly termed into six categories: assembly costs, disassembly costs, maintenance costs, form costs, material costs and process costs. A representation of the cost/economy module and the aggregation levels is given in figure 4.5.
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4.7.2 Assembly Costs
Assembly costs include the connection costs, labor cost, and tool cost. The selection of fasteners and tools are dependent on the form and material of the product and its components. The operator costs depend on the human factors and the assembly module described earlier in the framework.
4.7.3 Disassembly Costs
Disassembly costs include the tool cost and labor cost. These costs are incurred when a product is disassembled into its components.
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4.7.4 Maintenance Costs
Maintenance costs include the cost incurred during maintenance activities. These include the cost for maintenance procedures, labor costs for maintenance, and parts of assembly costs and disassembly costs.
4.7.5 Form Cost Aggregation Level
Form cost aggregation level is associated with the costs that are required for the products or components to attain the form features such as shape, size, other geometrical features, accuracy, and surface features. The form cost is a precedent in determining the material cost and the process cost as it can suggest the viable options in these two aggregation levels. A classification of the form cost factors breakdown into determinants and design attributes is given in table 4.13.
Table 4.13. Form Cost breakdown
Design Attributes Design Factors Feature Shape, Size, Location, Accuracy, Finish Surface Surface Roughness, Location, Inclination Aesthetics Product Specific
4.7.6 Material Costs and Process Costs
Material selection is a complicated process that has to be made early in the design process. The many constraints to material selection would be the forms and features, functionality, process capability, and the associated costs. Once the material selection is done, these constrains again apply to the processes that can be applied in their realization. The factors that affect material and
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process costs are form and function of the product, material properties, and the associated costs with the process that is required to attain the forms and functions, of the product.
4.7.7 Design for Environment: Environment Module
End–of–life (EOL) concerns exist in every product design and development process. Consumer demands, competition, and legislations are major factors that incorporate the need for design for environment. Design for Environment includes different product development activities, such as appropriate material selection, usability analysis for environmental friendliness, designing for energy efficiency, adoption of environmental friendly manufacturing methods, designing for end-of-life, improvement in packaging, and removal of toxic materials during manufacturing purposes. The design for environment module in the framework categorizes the end–of–life objectives of a product into 6 different categories and lists the factors that affect the design process with environmental considerations in mind. Table 4.14 lists the end-of-life strategies and the design considerations for design for environment process. The design considerations for the
EOL strategies can be derived from the individual modules from where the design factors have been derived.
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Table 4.14. EOL strategies and design considerations in design for environment
EOL Strategy Modular Incorporation
Reuse Maintainability, Assembly / Disassembly
Maintainability , Assembly/ Disassembly, Functionality, Service Usability
Remanufacture Disassembly, Materials
Recycling with Disassembly Disassembly, Materials
Recycling without Disassembly Materials
Disposal Materials
Reuse is the EOL strategy in which a part or component is dissembled from a product structure to be used on a need to need basis. This involves little to no up-gradation or down-gradation of technology or any design modification.
Service refer to the processes by which the life and durability of a product is increased by repair or maintenance activities, or by replacing the dysfunctional parts of a product.
Remanufacturing is the EOL strategy in which a component or part is disassembled from a product structure, subject to certain design modifications which involve certain technological up- gradation or down-gradation.
In recycling, the only concern is for the material that is used in the manufacturing of the specific part or product. In some cases, the product is disassembled and certain parts are recycled
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according to the material which they are made from (e.g.: heavy machinery). The disassembly process eases the separation of valuable materials from contaminants and other toxic materials.
In recycling without disassembly, the product is recycled as a whole (e.g.: a notebook made of paper). For products that are made of multiple materials, several methods, such as filtering, magnetic separation, etc. are employed in order to separate materials from one another.
The three aggregation levels for design factors in the environmental module are: Human Factors,
Material Factors and Pollution Factors.
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Figure 4.6 categorizes the environmental concerns into aggregation levels and their classifications.
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4.8 Design for Quality (Quality Module)
Quality is an important product design criterion and directly relates to pricing, customer response, loyalty, profitability, and, in turn, their overall success. Radford [55] describes quality in engineering and industry to be a single or group of characteristics that distinguish the services or products of one manufacturer from that of its competitors. The determinants for the quality module have been derived and modified from the nine dimensions of quality by Garvin [24] and are listed in table 4.15. The design factors for each determinant can be adapted from the earlier modules.
Table 4.15 Determinants and aggregation levels in Quality Module
Determinants Aggregation Levels Dependent Module
Functionality Performance Function-Information
Usability Response, Features Usability
Reliability Conformance, Durability Reliability
Maintainability Service Maintenance
Aesthetics, Usability, Functionality, Material Material Maintainability, Reliability
4.8.1 Functionality requirements for product quality
The design factors listed in the functionality module can be used to determine whether the product adheres to its primary purpose, thus ensuring the quality of performance.
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4.8.2 Usability requirements for product quality
The usability requirements for quality include the response of the product to the user and the features that make these responses receive a favorable reaction from the user.
4.8.3 Reliability requirements for product quality
The reliability requirements for quality in a product relate to the conformance of the product to its specs and the durability of the product during its expected life cycle.
4.8.4 Maintainability requirements for product quality
The maintainability requirements, and the means to achieve them, form an important part of the product quality structure as this restores the depleted functionality and usability levels as the product life cycle progress.
4.8.5 Material requirements for product quality
The material determinant directly contributes to all other determinants required for the product quality. The choice of material is important for customer satisfaction, aesthetic features as well as other determinants. The design factors for this section can be derived from the material module.
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Chapter 5: Conclusion
The framework for product design establishes the design modules, design factors and their inter- connection for 9 different design goals: Functionality, Materials, Assembly/Disassembly,
Maintenance, Usability, Reliability, Cost, Environment and Quality. The framework is the first of its kind in the field of product design by attempting to establish design modules, design factors and their inter-dependence. The framework is also expandable for all the design modules so that any new identifiable design factors could be incorporated into it.
This work is the first step towards developing a comprehensive interactive system to guide designers to improve their design based on the DFX methodology. The specific contribution of this framework towards this interactive system is that it forms the basis for the functioning of this system. The system will derive the design factors from the design modules and use these design factors to provide design recommendations and modifications to the designer.
Figure 5.1 (A) represents the framework with the modules and the aggregation levels while
Figure 5.1 (B) represents the modules, aggregation levels, and the design factors.
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Chapter 6: Future Work
6.1 Development of an interactive designer aid system
As represented in Figure 5.1 (B), the design factors can be further broken down into design parameters, which are the different values (both quantitative and qualitative) these factors could take, depending on the specifications of a product. The next step involves the development of an interactive system that will aid a designer by providing design recommendations and modifications by drawing out information from the framework. The proposed interactive system sits on top of an existing CAD software package. The interaction with the designer is enabled by the use of a set of menu driven questionnaire to which a response from the user is required.
6.2 Role of the framework in the interactive system
The framework is the base from which the proposed interactive system draws information from, and it is this information that will be used to provide design recommendations and modifications based on the response of the designer to an interactive questionnaire. The following section explains in detail as to how the system will draw information from the framework.
6.3 Capturing functional knowledge: deriving information from the framework
In section 4.1, it has been stated that there are two types of components in products: standard components and custom components. For a standard component such as bolt, nut or screw, the
Function-information Module in the interactive system will understand its function and capture the functional knowledge accordingly. Figure 6.1 represents the captured functional knowledge for a standard component, a screw bolt.
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Figure 6.1. Captured functional knowledge of a standard component
For a custom component, the framework categorizes the design factors into three aggregation levels: shape, performance and force-motion, as listed in table 4.1. The Function-Information module of the system uses this information in the framework to capture the functional knowledge of a custom component.
Figure 6.2 depicts an everyday ball point pen disassembled into 7 constituent parts. Part number
3 is the body of the pen, which is the custom component in consideration.
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Figure 6.2. Sample product: Disassembly of a ball point pen
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Figure 6.3 depicts how the shape attributes of the custom component are extracted by the intearactive system by drawing out information in the framework. Once the designer design the component in CAD, the Function-Information Module will assess the component, and from the shape attributes in the framework, it will identify the geometry, features and finishing to be cylindrical, slot and internal threading and smooth finishing respectively.
Figure 6.4 depicts the extraction of the material aggregation level in the performance attribute listed in the Function-Information Module of the framework. The interatcive system will use information from the user about strength and weight and use the framework to list out the list of material properties to be considered, which in this case would turn out to be compressive strength, density and volume.
Figure 6.5 depicts the extraction of force-motion attributes of the component by information from the framework. The interactive system will present the designer with choices for forces and motions, which will in turn act as constraints in the forthcoming modules.
Figures 6.3,6.4 and 6.5 represents how the framework will aid in the development of the proposed interactive system by providing information on the design factors and aggregation levels for all the modules in the system.
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Figure 6.3 Extraction of shape attributes for the custom component: The interactive system extracts the features of the custom component by using the information listed in the framework
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Figure 6.4. Extraction of performance attributes for the custom component: The interactive system derives the required information for the material aggregation level in the Function-Information Module of the framework
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Figure 6.5. Extraction of force-motion attributes for the custom component: The interactive system presents the designer with the force-motion attributes from
the framework and prompts the selection of the force and motion constraints to be applied in the forthcoming modules 67
Figure 6.6 shows the functional knowledge of standard and custom components as extracted by the Function-Information Module of the interactive system, with the aid of the framework. The functional knowledge of the custom component has been identified for shape, performance and force-motion attributes. As a next step in the future, the intreactive system would provide a menu driven questionnaire to enable the designer to modify the design, and in turn, to provide design recommendations. Figure 6.7 represents a sample of the menu driven questionnaire.
Figure 6.6. Captured functional knowledge of standard and custom components
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Figure 6.7. Menu driven questionnaire for the functioning of the intreactive system
The previous figure represents the questionnaire for the Funciton-Information Module in the interactive system. Each module will contain a set of questions to enable the functioning of the system, which is aiding the designer by providing design reccomendations and suggestions.
6.4 Interaction between modules in the system
It is intended for the different modules in the proposed system to interact with each other based on the information extracted from the design, and the response of the designer to the questionnaire. As an expample, for the materail information that the desiger entered in the
Function-Information Module, certain material families are chosen or eliminated in the Material
Module. This elimination occur on the basis of desirable material properties, which can be derived from the framework. An example is shown in figure 6.8
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Figure 6.8. Interaction between Function-Information and Material Modules
In the previous figure, once the material requirements for a product or design has been obtained from the material aggregation level in the perfromace attributes of the Function-Information
Module (low toxicity, low corrosion, high strenght to weight ratio, etc. in Figure 6.7), the conflicting material properties are flagged in the material module, which contain all the infromation of these properties from the framework.In this case, the plastic and alumium family is shortlisted and the designer selects the plastic family, then thermo plastics, polystyrene and so on. This depicts how the framework will aid in the interaction between different modules in the system.
6.5 Final Remarks
The previous sections in this chapter explained how the framework would contribute towards the establishtment of an interactive system intended to aid designers by providing design reccomendations and solutions. The framework is always expandable, meaning more information can be added to it when any other design factors are discovered. The proposed system, when
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completed, is expected to be the first of its kind and will greatly help a designer in the achievement of his intention, which is a well designed product or component.
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