2.5 Function, material, shape, and process 9 views of enthusiasts, and try out candidate-bikes yourself. And if you do not like them you go back one or more steps. Only when a match between your need and an available product is found do you make a final selection. The materials input does not end with the establishment of production. Products fail in service, and failures contain information. It is an imprudent manufacture er who does not collect and analyze data on failures. Often this points to the misuse of a material, one that redesign or re-selection can eliminate 2.5 Function, material, shape, and process The selection of a material and process cannot be separated from the choice of shape. We use the word"shape"to include the external, macro-shape, and when necessary-the internal, or micro-shape, as in a honeycomb or cellular structure. To make the shape, the material is subjected to processes that, col lectively, we shall call manufacture: they include primary forming processes (like casting and forging), material removal processes (machining, drilling) finishing processes(such as polishing) and joining processes(e.g. welding) Function, material, shape and process interact(Figure 2.6). Function dictates he choice of both material and shape Process is influenced by the material: by its formability, machinability, weldability, heat-treatability, and so on. Process obviously interacts with shape -the e process determines the shape, the size, the precision and, of course, the cost. The interactions are two-way: specifi cation of shape restricts the choice of material and process; but equally the Function Material Shape Process Figure 2.6 The central problem of materials selection in mechanical design: the interaction between function, material, shape and process
views of enthusiasts, and try out candidate-bikes yourself. And if you do not like them you go back one or more steps. Only when a match between your need and an available product is found do you make a final selection. The materials input does not end with the establishment of production. Products fail in service, and failures contain information. It is an imprudent manufacturer who does not collect and analyze data on failures. Often this points to the misuse of a material, one that redesign or re-selection can eliminate. 2.5 Function, material, shape, and process The selection of a material and process cannot be separated from the choice of shape. We use the word ‘‘shape’’ to include the external, macro-shape, and — when necessary — the internal, or micro-shape, as in a honeycomb or cellular structure. To make the shape, the material is subjected to processes that, collectively, we shall call manufacture: they include primary forming processes (like casting and forging), material removal processes (machining, drilling), finishing processes (such as polishing) and joining processes (e.g. welding). Function, material, shape and process interact (Figure 2.6). Function dictates the choice of both material and shape. Process is influenced by the material: by its formability, machinability, weldability, heat-treatability, and so on. Process obviously interacts with shape — the process determines the shape, the size, the precision and, of course, the cost. The interactions are two-way: specifi- cation of shape restricts the choice of material and process; but equally the Function Material Process Shape Figure 2.6 The central problem of materials selection in mechanical design: the interaction between function, material, shape and process. 2.5 Function, material, shape, and process 19
20 Chapter 2 The design process specification of process limits the materials you can use and the shapes they can take. The more sophisticated the design, the tighter the specifications and the greater the interactions. It is like making wine: to make cooking wine, almost any grape and fermentation process will do; to make champagne, both grape and process must be tightly constrained The interaction between function, material, shape, and process lies at the heart of the material selection process. But first, a case study to illustrate the design process 2.6 Case study: devices to open corked bottles Wine, like cheese, is one of man's improvements on nature. And ever since man has cared about wine, he has cared about cork to keep it safely sealed in flasks and bottles. "Corticum.. demovebit amphorae “ Uncork the ng Horace(27 BC)to celebrate the anniversary of his miraculous escape from death by a falling tree. But how did he do it? A corked bottle creates a market need: it is the need to gain access to the inside. We might state it thus: "a device is required to pull corks from wine bottles. But hold on. The need must be expressed in solution-neutral form, and this is not. The aim is to gain access to the wine; our statement implies that this will be done by removing the cork, and that it will be removed by pulling There could be other ways. So we will try again: "A device is required to allow access to wine in a corked bottle"(Figure 2.7)and one might add, "with convenience, at modest cost, and without contaminating the wine. igure 2.7 The market need: a device is sought to allow access to wine contained in a corked bottle Horace, Q. 27 BC, Odes, Book Ill, Ode 8, line 10
specification of process limits the materials you can use and the shapes they can take. The more sophisticated the design, the tighter the specifications and the greater the interactions. It is like making wine: to make cooking wine, almost any grape and fermentation process will do; to make champagne, both grape and process must be tightly constrained. The interaction between function, material, shape, and process lies at the heart of the material selection process. But first, a case study to illustrate the design process. 2.6 Case study: devices to open corked bottles Wine, like cheese, is one of man’s improvements on nature. And ever since man has cared about wine, he has cared about cork to keep it safely sealed in flasks and bottles. ‘‘Corticum ... demovebit amphorae ... ’’ — ‘‘Uncork the amphora ... ’’ sang Horace2 (27 BC) to celebrate the anniversary of his miraculous escape from death by a falling tree. But how did he do it? A corked bottle creates a market need: it is the need to gain access to the wine inside. We might state it thus: ‘‘A device is required to pull corks from wine bottles.’’ But hold on. The need must be expressed in solution-neutral form, and this is not. The aim is to gain access to the wine; our statement implies that this will be done by removing the cork, and that it will be removed by pulling. There could be other ways. So we will try again: ‘‘A device is required to allow access to wine in a corked bottle’’ (Figure 2.7) and one might add, ‘‘with convenience, at modest cost, and without contaminating the wine.’’ ? Figure 2.7 The market need: a device is sought to allow access to wine contained in a corked bottle. 2 Horace, Q. 27 BC, Odes, Book III, Ode 8, line 10. 20 Chapter 2 The design process
2.6 Case study: devices to open corked bottles 且夏 igure 2.8 Five possible concepts, illustrating physical principles, to fill the need expressed by Figure 2.9 Working principles for implementing the first three schemes of Figure 2.8 Five co for doing this are shown in 2.8. In order. the remove the cork by axial traction(= pulling); to remove it by shear tractions; to push it out from below; to pulverizing it; and to by-pass it altogether-by knocking the neck off the bottle'perhal A Victorian invention for opening old port, the cork of which may become brittle with age and alcohol- absorption, involved ring-shaped tongs. The tongs were heated red on an open fire, then clamped onto the cold neck of the bottle. The thermal shock removed the neck cleanly and neatly
Five concepts for doing this are shown in Figure 2.8. In order, they are to remove the cork by axial traction ( ¼ pulling); to remove it by shear tractions; to push it out from below; to pulverizing it; and to by-pass it altogether — by knocking the neck off the bottle3 perhaps. (a) (b) (d) (e) (c) Figure 2.8 Five possible concepts, illustrating physical principles, to fill the need expressed by Figure 2.7. (a) (b) (c) Figure 2.9 Working principles for implementing the first three schemes of Figure 2.8. 3 A Victorian invention for opening old port, the cork of which may become brittle with age and alcoholabsorption, involved ring-shaped tongs. The tongs were heated red on an open fire, then clamped onto the cold neck of the bottle. The thermal shock removed the neck cleanly and neatly. 2.6 Case study: devices to open corked bottles 21
22 Chapter 2 The design process igure 2.10 Cork removers that employ the working principles of Figure 2.9: (a) direct pull;(b)gear lever, driven into the cork;(d)shear blade systems;(e)pressure-induced removal systemswis ew-assisted pull;(c)spring-assisted pull (a spring in the body is compressed as the screv Numerous devices exist to achieve the first three of these. The others are used too, though generally only in moments of desperation. We shall eliminate these on the grounds that they might contaminate the wine, and examine the others more closely, exploring working principles. Figure 2.9 shows one for each of
Numerous devices exist to achieve the first three of these. The others are used too, though generally only in moments of desperation. We shall eliminate these on the grounds that they might contaminate the wine, and examine the others more closely, exploring working principles. Figure 2.9 shows one for each of (a) (b) (c) (d) (e) Figure 2.10 Cork removers that employ the working principles of Figure 2.9: (a) direct pull; (b) gear lever, screw-assisted pull; (c) spring-assisted pull (a spring in the body is compressed as the screw is driven into the cork; (d) shear blade systems; (e) pressure-induced removal systems. 22 Chapter 2 The design process
2.6 Case study: devices to open corked bottles 23 force Shaft Shear blades Geared pull Direct push Levered pu Figure 2.1 The function structure and working principles of cork re gure 2.12 Embodiment sketches for four concepts: direct pull, levered pull, geared pull and sprits me assisted pull. Each system is made up of components that perform a sub-function equirements of these sub-functions are the inputs to the materials selection method
(a) (b) (c) (d) Figure 2.12 Embodiment sketches for four concepts: direct pull, levered pull, geared pull and springassisted pull. Each system is made up of components that perform a sub-function. The requirements of these sub-functions are the inputs to the materials selection method. Direct pull Levered pull Geared pull Direct push Levered push Shaft Linkage Gas injection Screw Shear blades Gas pressure Generate force Transmit force Apply force to cork Figure 2.11 The function structure and working principles of cork removers. 2.6 Case study: devices to open corked bottles 23