MME445: Lecture 02 The design process. A. K. M. B. Rashid Professor, Department of MME BUET, Dhaka. Learning Objectives. Resources

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1 MME445: Lecture 02 The design process A. K. M. B. Rashid Professor, Department of MME BUET, Dhaka Learning Objectives Knowledge & Understanding Understanding of the functional structure of a design process and the types of design tools and materials data required for design Skills & Abilities Ability to determine the elements of a design flow chart and identify the design tools and materials data required for design Values & Attitudes Appreciation of the design process and the need for design tools and materials data in design Resources M F Ashby, Materials Selection in Mechanical Design, 4 th Ed., Ch. 02 1

2 Outline of this lecture. Introduction The design process Types of design Design tools and materials data Function, material, shape, and process Case study Introduction We are primarily concerned here with mechanical design: the physical principles, the proper functioning, and the production of mechanical system. this does not ignore industrial design pattern, colour, texture, and (above all) consumer appeal The optimum starting point in product development 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 process that is design-led. that means it uses, as inputs, the functional requirements of the design. 2

The design process The starting point of a design is a market need or a new idea; the end point is the full specification of a product that fills the need or embodies the idea.

3 The design process The starting point of a design is a market need or a new idea; the end point is the full 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 this form: A device is required to perform task X expressed as a set of design requirements. solution is neutral to avoid narrow thinking constrained by preconceptions Market Need: design requirement Concept Embodiment Detail iterate Product Specification 3

Products are technical systems composed of sub-assemblies and components It is like describing a cat (the system) as made up of one head, one body, one tail, four legs, and so on (the

4 Products are technical systems composed of sub-assemblies and components It is like describing a cat (the system) as made up of one head, one body, one tail, four legs, and so on (the sub-assemblies), each composed of components: femurs, quadriceps, claws, fur. useful way to analyze an existing design not of much help in the design process itself, that is, in devising new designs This design converts inputs into outputs. e.g., an electric motor converts electrical energy into mechanical energy The system is broken down into interconnected sub-systems, each of which performs a specific function. The type of arrangement is called the function structure or function decomposition of the system, which gives a systematic assessment of design options. 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. 4

Market Need: design requirement Determine function structure Seek working principles Evaluate and select concepts Concept Develop layout, scale, form Model and analyse assemblies Evaluate and select

degree of functionality (market need), proper materials selection, aesthetics and price. Product Specification FIGURE 1 The design flow chart All that sounds well and good. If only it were so simple.

5 Market Need: design requirement Determine function structure Seek working principles Evaluate and select concepts Concept Develop layout, scale, form Model and analyse assemblies Evaluate and select layout Analyse components in detail Optimise performance and cost Final choice of material and process Embodiment Detail iterate Example of good design cell phones ipod These design employ a high degree of functionality (market need), proper materials selection, aesthetics and price. Product Specification FIGURE 1 The design flow chart All that sounds well and good. If only it were so simple. The linear process suggested in Fig. 1 obscures the strong coupling between the three stages. The consequences of choices made at the concept or the embodiment stages may not become apparent until the detail is examined. Iteration, looping back to explore alternatives, is an essential part of the design process. The process is complete when a compatible path from need to specification can be identified. Thus a key part of design, and of selecting materials for it, is flexibility, the ability to explore alternatives quickly. FIGURE 2 The convoluted path of design. Here the C-blobs represent concepts; the E-blobs, embodiments of the Cs; and the D-blobs, detailed realizations of the Es. 5

6 Types of design Original design New idea or working principle e.g., the ballpoint pen or the CD New materials can offer new, unique combinations of properties that enable original design. high-purity silicon enabled the transistor high-purity glass for the optical fiber high coercive-force magnets for the miniature earphone solid-state lasers for the compact disc The new material often suggests the new product. Sometimes, instead, the new product demands the development of a new material. nuclear technology drove the development of a series of new zirconium alloys and low-carbon stainless steels space technology stimulated the development of light weight composites gas turbine technology today drives development of high-temperature alloys and ceramic coatings. Original design sounds exciting, and it is. But most design is not like that. 6

7 Adaptive or developmental design Almost all designs are adaptive or developmental e.g., beverage cans, automobiles, Takes existing concept (product or product range) and, through a refinement in working principle, seeks to enhance performance reduce cost adapt it to changing market conditions. This type of design, too, is often made possible by developments in materials. polymers replacing metals in household appliances carbon fiber replacing wood in sports equipment Variant design Change of scale or dimension or detailing without change of function or method of achieving it desktop to laptop computer Scaling up of boilers or turbines Change of scale or circumstances of use may require change of material. small boats are made of fiberglass, large ships are made of steel small boilers are made of copper, large ones of steel subsonic planes are made of one alloy, supersonic of another Question: Microsoft Windows 10 What type of design is this? 7

8 So far we learned and be able to indentify... The design flow chart Functional structure of a technical system Types of design Design tools and materials data 8

Function, material, shape and process To make a shape, the material is subjected to the manufacturing processes. Primary forming processes (e.g., casting and forging) Material removal processes (machining, drilling) Joining processes (e.

Function influences material choice. Material choice influences processes. Process determines shape, size, precision, and, of course, cost.

9 Function, material, shape and process To make a shape, the material is subjected to the manufacturing processes. Primary forming processes (e.g., casting and forging) Material removal processes (machining, drilling) Joining processes (e.g., welding), and Finishing processes (e.g., painting or electroplating) The interaction between function, material, shape, and process lies at the heart of the material selection process. Function influences material choice. Material choice influences processes. Process determines shape, size, precision, and, of course, cost. The more sophisticated the design, the tighter the specifications and the greater the interactions. FIGURE 3 The central problem of materials selection in mechanical design: the interaction between function, material, process, and shape. Case study A simple design problem We need a design solution for a device that will allow us to gain access to the wine contained in a corked bottle. We need to express the above functional requirement of the design in a solution neutral fashion in a reasonably detailed need statement. A device is required to pull corks from wine bottles Is there anything wrong about this need statement? A device is required to allow access to wine in a corked bottle with convenience, at modest cost, and without contaminating the wine 9

axial traction or pulling shear traction high internal pressure Solutions (d) and (e) are feasible, but

How can we define the requirements for solutions (a) through (c) into a device?

concepts Axial traction a screw or similar device is threaded into the cork and axial traction is

Shear traction thin blades of an elastic material slide between the cork and bottle and the cork removed

10 A few ideas / concepts.. Solutions (a) through (c) are feasible and are implemented in devices available on the market. axial traction or pulling shear traction high internal pressure Solutions (d) and (e) are feasible, but can be eliminated on the ground that they have the potential of (dangerously) contaminating the wine. How can we define the requirements for solutions (a) through (c) into a device? pulverized cork break bottle neck (bypass coke) Working principles for implementing the first three concepts Axial traction a screw or similar device is threaded into the cork and axial traction is applied. Shear traction thin blades of an elastic material slide between the cork and bottle and the cork removed by traction when twisted and pulled axial traction or pulling shear traction high internal pressure High internal pressure the cork is pierced and gas (air) pumped into the bottle such that the cork is pushed out All solutions seek to apply a force and transmit this force to the cork such that it is removed from the bottle 10

Embodiment of the 1st concept Each of the solutions embodies the use of a screw with various means of applying the axial traction (a) direct, (b) via a lever, (c) via gears attached to beams, and (d)

11 Embodiment of the 1st concept Each of the solutions embodies the use of a screw with various means of applying the axial traction (a) direct, (b) via a lever, (c) via gears attached to beams, and (d) spring-assisted traction The embodiments identify the functional requirements of each component of the device, which might be expressed in statements such as A cheap screw to transmit a prescribed load to the cork A light lever (that is, a beam) to carry a prescribed bending moment A slender elastic blade that will not buckle when driven between the cork and the bottle neck (for concept 2) A thin, hollow needle, stiff and strong enough to penetrate a cork (for concept 3) The functional requirements of each one of the components are inputs to the materials selection through their respective design equations or requirements. 11

12 The function structure Detailed Design Detailed design of the lever of embodiment with material choice

13 Summary and conclusions Design is an iterative process. The starting point is a market need captured in a set of design requirements. Concepts for a product that meet the need are devised. If initial estimates and exploration of alternatives suggest that the concept is viable, the design proceeds to the embodiment stage: working principles are selected, size and layout are decided, and initial estimates of performance and cost are made. If the outcome is successful, designer proceeds to the detailed design stage: optimization of performance, full analysis of critical components, preparation of detailed production drawings (usually as CAD files), and specifications of tolerance, precision, assembly, and finishing methods. Materials selection enters at each stage, but at different levels of breadth and precision. Data exist that meet the needs of all these levels. Each level requires its own data management scheme. The management system must be design-led, yet must recognize the richness of choice and embrace the complex interaction between the material, its shape, the process by which it is given that shape, and the function it is required to perform. And it must allow rapid iteration back-looping when a particular path proves to be unprofitable. Tools now exist to help with all of this. 13

14 But given this complexity, why not opt for the safe bet : Stick to what you used before? Many have chosen that option. Off them, few are still in business. Next Class MME445: Lecture 03 Engineering materials and their properties 14

The design process. 2.2 The design process. 2.1 Introduction and synopsis

The design process. 2.2 The design process. 2.1 Introduction and synopsis The design process 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