8 Chapter I Introduction Table 1. I Comparison of cost, power, and weight of vacuum cleaners Cleaner and Power eight Approximate Hand powered, Wood. canvas 10 240-$380 leather Mild steel ￡96$|50 Molded abs and f60$95 polypropylene Dyson, 1995 Polypropylene, 1200 ￡190$300 Costs have been adjusted to 1998 values, allowing for inflation. All this has happened within one lifetime. Competitive design requires the innovative use of new materials and the clever exploitation of their special properties, both engineering and aesthetic. Many manufacturers of vacuum cleaners failed to innovate and exploit; now they are extinct. That sombre thought prepares us for the chapters that follow in which we consider what they forgot: the optimum use of materials in design 1.5 Summary and conclusions The number of engineering materials is large: tens of thousands, at conservative estimate. The designer must select, from this vast menu, the f.a est suited to his task. This, without guidance, can be a difficult and haphazard business, so there is a temptation to choose the material that is "traditional"for the application: glass for bottles; steel cans. That choice may be safely con- servative, but it rejects the opportunity for innovation. Engineering material are evolving faster, and the choice is wider than ever before. Examples of products in which a new material has captured a market are as common as well-as plastic bottles. Or aluminium cans. Or polycarbonate eyeglass lenses. Or carbon-fiber golf club shafts. It is important in the early stage of design, or of re-design, to examine the full materials menu, not rejecting options merely because they are unfamiliar. That is what this book is about 1. 6 Further reading The history and evolution of materials A History of Technology(21 volumes), edited by Singer, C, Holmyard, E J, Hall, A.R. Williams, T L, and Hollister-Short, G. Oxford University Press (1954-2001)
All this has happened within one lifetime. Competitive design requires the innovative use of new materials and the clever exploitation of their special properties, both engineering and aesthetic. Many manufacturers of vacuum cleaners failed to innovate and exploit; now they are extinct. That sombre thought prepares us for the chapters that follow in which we consider what they forgot: the optimum use of materials in design. 1.5 Summary and conclusions The number of engineering materials is large: tens of thousands, at a conservative estimate. The designer must select, from this vast menu, the few best suited to his task. This, without guidance, can be a difficult and haphazard business, so there is a temptation to choose the material that is ‘‘traditional’’ for the application: glass for bottles; steel cans. That choice may be safely conservative, but it rejects the opportunity for innovation. Engineering materials are evolving faster, and the choice is wider than ever before. Examples of products in which a new material has captured a market are as common as — well — as plastic bottles. Or aluminium cans. Or polycarbonate eyeglass lenses. Or carbon-fiber golf club shafts. It is important in the early stage of design, or of re-design, to examine the full materials menu, not rejecting options merely because they are unfamiliar. That is what this book is about. 1.6 Further reading The history and evolution of materials A History of Technology (21 volumes), edited by Singer, C., Holmyard, E.J., Hall, A.R., Williams, T.I., and Hollister-Short, G. Oxford University Press (1954–2001) Table 1.1 Comparison of cost, power, and weight of vacuum cleaners Cleaner and date Dominant materials Power (W) Weight (kg) Approximate cost* Hand powered, 1900 Wood, canvas, leather 50 10 £240–$380 Cylinder, 1950 Mild steel 300 6 £96–$150 Cylinder, 1985 Molded ABS and polypropylene 800 4 £60–$95 Dyson, 1995 Polypropylene, polycarbonate, ABS 1200 6.3 £190–$300 *Costs have been adjusted to 1998 values, allowing for inflation. 8 Chapter 1 Introduction
1.6 Further reading 9 Oxford, UK. ISSN 0307-5451(A compilation of essays on aspects of technology including materials.) Delmonte, J (1985) Origins of Materials and Processes, Technomic Publishing Com- pany, Pennsylvania, USA. ISBN 87762-420-8. (A compendium of information on when materials were first used, any by whom.) Dowson, D.(1998)History of Tribology, Professional Engineering Publishing Ltd, London, UK. ISBN 1-86058-070-X(A monumental work detailing the history of devices limited by friction and wear, and the development of an understanding of these phenomena. Emsley, J (1998), Molecules at an Exhibition, Oxford University Press, Oxford, UK. ISBN 0-19-286206-5.(Popular science writing at its best: intelligible, accurate, simple and clear. The book is exceptional for its range. The message is that molecules, often meaning materials, influence our health, our lives, the things we make and the Michaelis, R. R (1992)editor"Gold: art, science and technology", and"Focus on gold Interdisciplinary Science Reviews, volume 17 numbers 3 and 4. ISSN 0308-0188 (A comprehensive survey of the history, mystique, associations and uses of gold. The Encyclopaedia Britannica, 11th edition (1910). The Encyclopaedia Britannica <Ompany, New York, USA (Connoisseurs will tell you that in its 11th edition the cyclopaedia Britannica reached a peak of excellence which has not since bee equalled, though subsequent editions are still usable. Tylecoate, R F (1992)A History of Metallurgy, 2nd edition, The Institute of Materials, London, UK. ISBN 0-904357-066(A total-immersion course in the history of the extraction and use of metals from 6000BC to 1976, told by an author with forensic and love of detail. And on vacuum cleaners Forty, A (1986)Objects of Desire-design in society since 1750, Thames and Hudson, London, UK, p 174 et seq. ISBN 0-500-27412-6. (A refreshing survey of the design istory of printed fabrics, domestic products, office equipment and transport system The book is mercifully free of eulogies about designers, and focuses on what industrial design does, rather than who did it. The black and white illustrations are disappointing. mostly drawn from the late 19th or early 20th centuries, with few examples of con- emporary design
Oxford, UK. ISSN 0307–5451. (A compilation of essays on aspects of technology, including materials.) Delmonte, J. (1985) Origins of Materials and Processes, Technomic Publishing Company, Pennsylvania, USA. ISBN 87762-420-8. (A compendium of information on when materials were first used, any by whom.) Dowson, D. (1998) History of Tribology, Professional Engineering Publishing Ltd., London, UK. ISBN 1-86058-070-X. (A monumental work detailing the history of devices limited by friction and wear, and the development of an understanding of these phenomena.) Emsley, J. (1998), Molecules at an Exhibition, Oxford University Press, Oxford, UK. ISBN 0-19-286206-5. (Popular science writing at its best: intelligible, accurate, simple and clear. The book is exceptional for its range. The message is that molecules, often meaning materials, influence our health, our lives, the things we make and the things we use.) Michaelis, R.R. (1992) editor ‘‘Gold: art, science and technology’’, and ‘‘Focus on gold’’, Interdisciplinary Science Reviews, volume 17 numbers 3 and 4. ISSN 0308–0188. (A comprehensive survey of the history, mystique, associations and uses of gold.) The Encyclopaedia Britannica, 11th edition (1910). The Encyclopaedia Britannica Company, New York, USA. (Connoisseurs will tell you that in its 11th edition the Encyclopaedia Britannica reached a peak of excellence which has not since been equalled, though subsequent editions are still usable.) Tylecoate, R.F. (1992) A History of Metallurgy, 2nd edition, The Institute of Materials, London, UK. ISBN 0-904357-066. (A total-immersion course in the history of the extraction and use of metals from 6000BC to 1976, told by an author with forensic talent and love of detail.) And on vacuum cleaners Forty, A. (1986) Objects of Desire — design in society since 1750, Thames and Hudson, London, UK, p. 174 et seq. ISBN 0-500-27412-6. (A refreshing survey of the design history of printed fabrics, domestic products, office equipment and transport system. The book is mercifully free of eulogies about designers, and focuses on what industrial design does, rather than who did it. The black and white illustrations are disappointing, mostly drawn from the late 19th or early 20th centuries, with few examples of contemporary design.) 1.6 Further reading 9
Chapter 2 The design process Market need design requirements Design tools Material data eeds Data for ALL material Concept Viability studies and det Geometric modelling Data for a suBSEt of Simulations methods Embodiment precision and detail Cost modellin Componenet modelling Data for ONE material Detail DFM. DFA Product specification Chapter contents 2.1 Introduction and synopsis 12 2.3 Types of design 2.4 Design tools and materials data 17 2.5 Function, material, shape, and process 2.6 Case study: devices to open corked bottles 20 2.7 Summary and conclusions 2.8 Further reading 25
Data for ALL materials, low precision and detail Data for a SUBSET of materials, higher precision and detail Data for ONE material, highest precision and detail Function modelling Viabiliey studies Approximate analysis Geometric modelling Simulations methods Cost modelling Componenet modelling Finite-element modelling (FEM) DFM, DFA Market need: design requirements Product specification Embodiment Detail Concept Material data needs Design tools Chapter contents 2.1 Introduction and synopsis 12 2.2 The design process 12 2.3 Types of design 16 2.4 Design tools and materials data 17 2.5 Function, material, shape, and process 19 2.6 Case study: devices to open corked bottles 20 2.7 Summary and conclusions 24 2.8 Further reading 25 Chapter 2 The design process
12 Chapter 2 The design process 2.1 Introduction and synopsis It is mechanical design with which we are primarily concerned here; it deals ith the physical principles, the proper functioning and the production of mechanical systems. This does not mean that we ignore industrial design, which speaks of pattern, color, texture, and (above all) consumer appeal-but that comes later. The starting point is good mechanical design, and the ways in which the selection of materials and processes contribute to it. Our aim is to develop a methodology for selecting materials and processes that is design-led; that is, the selection uses, as inputs, the functional require ments of the design. To do so we must first look briefly at design itself. Like most technical fields it is encrusted with its own special jargon, some of it bordering on the incomprehensible. We need very little, but it cannot all be avoided. This chapter introduces some of the words and phrases -the vocabulary -of design, the stages in its implementation, and the ways in which materials selection links with these 2.2 The design process The starting point is a market need or a new idea; the end point is the full product specification of a product that fills the need or embodies the idea. a need must be identified before it can be met. it is essential to define the need precisely, that is, to formulate a need statement, often in the form: "a device is required to perform task X", expressed as a set of design requirements. Writers n design emphasize that the statement and its elaboration in the design requirements should be solution-neutral (i.e. they should not imply how the task will be done), to avoid narrow thinking limited by pre-conceptions. Between the need statement and the product specification he the Conceptions. set of stages shown in Figure 2.1: the stages of conceptual, embodiment and detailed designs, explained in a moment. The product itself is called a technical system. A technical system consists of sub-assemblies and components, put together in a way that performs the required task, as in the breakdown of Figure 2. 2. It is like describing a cat (the system)as made up of one head, one body, one tail, four legs, etc. (the sub- assemblies), each composed of components-femurs, quadriceps, claws, fur This decomposition is a useful way to analyze an existing design, but it is not of much help in the design process itself, that is, in the synthesis of new designs Better, for this purpose, is one based on the ideas of systems analysis. It thinks of the inputs, flows and outputs of information, energy, and materials, as in Figure 2.3. The design converts the inputs into the outputs. An electric motor converts electrical into mechanical energy; a forging press takes and reshapes material; a burglar alarm collects information and converts it to noise. In this approach, the system is broken down into connected sub-systems each of
2.1 Introduction and synopsis It is mechanical design with which we are primarily concerned here; it deals with the physical principles, the proper functioning and the production of mechanical systems. This does not mean that we ignore industrial design, which speaks of pattern, color, texture, and (above all) consumer appeal — but that comes later. The starting point is good mechanical design, and the ways in which the selection of materials and processes contribute to it. Our aim is to develop a methodology for selecting materials and processes that is design-led; that is, the selection uses, as inputs, the functional requirements of the design. To do so we must first look briefly at design itself. Like most technical fields it is encrusted with its own special jargon, some of it bordering on the incomprehensible. We need very little, but it cannot all be avoided. This chapter introduces some of the words and phrases — the vocabulary — of design, the stages in its implementation, and the ways in which materials selection links with these. 2.2 The design process The starting point is a market need or a new idea; the end point is the full product specification of a product that fills the need or embodies the idea. A need must be identified before it can be met. It is essential to define the need precisely, that is, to formulate a need statement, often in the form: ‘‘a device is required to perform task X’’, expressed as a set of design requirements. Writers on design emphasize that the statement and its elaboration in the design requirements should be solution-neutral (i.e. they should not imply how the task will be done), to avoid narrow thinking limited by pre-conceptions. Between the need statement and the product specification lie the set of stages shown in Figure 2.1: the stages of conceptual, embodiment and detailed designs, explained in a moment. The product itself is called a technical system. A technical system consists of sub-assemblies and components, put together in a way that performs the required task, as in the breakdown of Figure 2.2. It is like describing a cat (the system) as made up of one head, one body, one tail, four legs, etc. (the subassemblies), each composed of components — femurs, quadriceps, claws, fur. This decomposition is a useful way to analyze an existing design, but it is not of much help in the design process itself, that is, in the synthesis of new designs. Better, for this purpose, is one based on the ideas of systems analysis. It thinks of the inputs, flows and outputs of information, energy, and materials, as in Figure 2.3. The design converts the inputs into the outputs. An electric motor converts electrical into mechanical energy; a forging press takes and reshapes material; a burglar alarm collects information and converts it to noise. In this approach, the system is broken down into connected sub-systems each of 12 Chapter 2 The design process
2.2 The design process 3 Market need design requirements Define specification Concept Evaluate and select concepts les ze the functions Embodiment and select layouts Final choice of material and process ce and cost Detail Prepare detailed drawings Product Figure 2.1 The design flow chart The design proceeds from the identification of a market need, clarified as a set of design requirements, through concept, embodiment and detailed analysis to a which performs a specific function, as in Figure 2.3; the resulting arrangement is called the function-structure or function decomposition of the system. It is like describing a cat as an appropriate linkage of a respiratory system, a cardio- vascular system, a nervous system, a digestive system and so on. Alternative designs link the unit functions in alternative ways, combine functions, or split them. The function-structure gives a systematic way of assessing design The design proceeds by developing concepts to perform th e functions in function structure, each based on a working principle. At this, the conceptual design stage, all options are open: the designer considers alternative concepts and the ways in which these might be separated or combined. The next stage, embodiment, takes the promising concepts and seeks to analyze their operation at an approximate level. This involves sizing the components, and selecting materials that will perform properly in the ranges of stress, temperature, and environment suggested by the design requirements, examining the implications for performance and cost. The embodiment stage ends with a feasible layout, which is then passed to the detailed design stage. Here specifications for each
which performs a specific function, as in Figure 2.3; the resulting arrangement is called the function-structure or function decomposition of the system. It is like describing a cat as an appropriate linkage of a respiratory system, a cardiovascular system, a nervous system, a digestive system and so on. Alternative designs link the unit functions in alternative ways, combine functions, or split them. The function-structure gives a systematic way of assessing design options. The design proceeds by developing concepts to perform the functions in the function structure, each based on a working principle. At this, the conceptual design stage, all options are open: the designer considers alternative concepts and the ways in which these might be separated or combined. The next stage, embodiment, takes the promising concepts and seeks to analyze their operation at an approximate level. This involves sizing the components, and selecting materials that will perform properly in the ranges of stress, temperature, and environment suggested by the design requirements, examining the implications for performance and cost. The embodiment stage ends with a feasible layout, which is then passed to the detailed design stage. Here specifications for each Develop layout, scale, form Model and analyze assemblies Optimize the functions Evaluate and select layouts Analyze components in detail Final choice of material and process Opimize performance and cost Prepare detailed drawings Market need: design requirements Product specification Iterate Define specification Determine function structure Seek working principles Evaluate and select concepts Embodiment Detail Concept Figure 2.1 The design flow chart. The design proceeds from the identification of a market need, clarified as a set of design requirements, through concept, embodiment and detailed analysis to a product specification. 2.2 The design process 13