PRODUCT DESIGN

Classifications of Machine Design

The machine design may be classified as follows :

1. Adaptive design. In most cases, the designer’s work is concerned with adaptation of existing designs. This type of design needs no special knowledge or skill and can be attempted by designers of ordinary technical training. The designer only makes minor alternation or modification in the existing designs of the product.

2. Development design. This type of design needs considerable scientific training and design ability in order to modify the existing designs into a new idea by adopting a new material or different method of manufacture. In this case, though the designer starts from the existing design, but the final product may differ quite markedly from the original product.

3. New design. This type of design needs lot of research, technical ability and creative thinking. Only those designers who have personal qualities of a sufficiently high order can take up the work of a new design.

The designs, depending upon the methods used, may be classified as follows :

(a) Rational design. This type of design depends upon mathematical formulae of principle of

mechanics.

(b) Empirical design. This type of design depends upon empirical formulae based on the practice and past experience.

(c) Industrial design. This type of design depends upon the production aspects to manufacture any machine component in the industry.

(d) Optimum design. It is the best design for the given objective function under the specified constraints. It may be achieved by minimising the undesirable effects.

(e) System design. It is the design of any complex mechanical system like a motor car.

(f) Element design. It is the design of any element of the mechanical system like piston, crankshaft, connecting rod, etc.

(g) Computer aided design. This type of design depends upon the use of computer systems to assist in the creation, modification, analysis and optimisation of a design.

A TEXTBOOK OF Machine Design

(S.I. UNITS)

[A Textbook for the Students of B.E. / B.Tech.,

U.P.S.C. (Engg. Services); Section ‘B’ of A.M.I.E. (I)]

2005

EURASIA PUBLISHING HOUSE (PVT.) LTD.

RAM NAGAR, NEW DELHI-110 055

Computer-Aided Design and Manufacture of Injection Forging

The design activity is responsible not only for the performance and appearance of the product but also for the cost of the component. Design, therefore, cannot be an isolated activity but must address all available manufacturing routes, with a view to optimizing the quality and cost of the component. With reference to nett-forming, the design exercise is conducted not only to specify the component-form but also to address all manufacturing constraints—machine, material, tooling, and processing conditions.

Computer-aided “design for manufacture” is currently the main form of implementing of the “concurrent

engineering.” To enable this, CAD/CAM is popularly used as a design approach. Using CAD/CAM

approaches, simultaneous design would be effected efficiently by supporting the designer with information

on all possible resources required for the design and manufacture of components. Some CAD/CAM

systems [42] have demonstrated the potential for the development into decision-support systems for

component/tool design.

Computer-aided design and manufacture for nett-forming by injection forging is being developed as

an aspect of research associated with the development of a decision-support system [64].

Methodology

In order to develop a decision-support system for component/tool design using a CAD/CAM approach, several design/evaluation methods have been developed [58, 60, 64–68]. These are described briefly in the following texts.

Geometric Modeling

The popular strategy used for the development of the design-support systems for forging was to evolve

a 2D-CAD system for component and tool design. The system was linked to a knowledge-based system

to enable the evaluation of manufacturability. Subsequent to the evaluation of the geometry, the component

was transferred to a CAD software to enable detailed design. This approach required the design to operate in several software environments. An integrated system, supported by solid modeling, would enable design and assessment of a component more efficiently. A solid modeling-approach—principal feature modeling—was used to enable component-design for forging within a solid modeling environment [65, 66]; the approach enables integration of currently available 2D-based knowledge-based systems.

Design for manufacture requires that the component form is specified in a modular form in order to enable the evaluation of the design. The component may be defined as a combination of primitive forms as is the case in “design by features;” alternatively, the primitive forms which constitute the component may be extracted and identified automatically. Unfortunately, both these approaches are currently at a stage of refinement which only allows their applications to a limited range of component forms. Principal feature modeling [67] combines the strategies of both “design by feature” and “feature recognition” to enable efficient modeling and feature manipulation; the approach was proven to be particularly efficient for the modeling of forging/machining components [65]. Designing is attended to with reference to a prescribed set of performance requirements rather than to prescribed form features. The principal features, which represent the principal geometric profiles of a component, may be defined by the designer using arbitrary geometry—a group of curves on a plane or a curved surface. The principal features which have been generated are linked, exclusively, to a set of prescribed attributes which are catalogued in a database.

The solid model of the component may be created by geometric manipulation of a principal feature; several principal features may be defined for more complex components. Subsequent to the definition of the principal features for a particular component; local features may be added to produce the first iteration of the “performance” model of the component. The form of the additional features is generated

by the modification of the principal geometric entities; these additional features are extracted and

classified as individual manufacturing features. In circumstances where components cannot be modeled by

defining principal features, the model can be created by other approaches. This will enable the prescription

of the principal feature by the extraction of the curves on a feature plane, which is prescribed by the designer. In comparison with the “design by feature” approach, the proposed approach [67] does not require a pre-defined feature library that would constrain the flexibility of the system. Further, the difficulty and complexity of the routines for the recognition of form features are reduced since the principal features, which are recorded in the system, provide auxiliary geometric and topologic information of the component model; this simplifies the recognition of manufacturing features.

COMPUTER-AIDED DESIGN,

ENGINEERING, AND MANUFACTURING

Systems Techniques And Applications

VOLUME

V I

Editor

CORNELIUS LEONDES

Boca Raton London New York Washington, D.C.

CRC Press

MANUFACTURING

SYSTEMS PROCESSES

Design

To design is either to formulate a plan for the satisfaction of a specified need or to solve a problem. If the plan results in the creation of something having a physical reality, then the product must be functional, safe, reliable, competitive, usable, manufacturable, and marketable.

Design is an innovative and highly iterative process. It is also a decision-making

process. Decisions sometimes have to be made with too little information, occasionally with just the right amount of information, or with an excess of partially contradictory information. Decisions are sometimes made tentatively, with the right reserved to adjust as more becomes known. The point is that the engineering designer has to be personally comfortable with a decision-making, problem-solving role.

Design is a communication-intensive activity in which both words and pictures are used, and written and oral forms are employed. Engineers have to communicate effectively and work with people of many disciplines. These are important skills, and an engineer’s success depends on them.

A designer’s personal resources of creativeness, communicative ability, and problemsolving skill are intertwined with knowledge of technology and first principles.

Engineering tools (such as mathematics, statistics, computers, graphics, and languages) are combined to produce a plan that, when carried out, produces a product that is functional, safe, reliable, competitive, usable, manufacturable, and marketable, regardless of who builds it or who uses it.

Mechanical Engineering

McGraw−Hill Primis

ISBN: 0−390−76487−6

Text:

Shigley’s Mechanical Engineering Design,

Eighth Edition

Budynas−Nisbett

Shigley’s Mechanical Engineering Design,

Eighth Edition

Budynas−Nisbett

McGraw -Hill

Design Activities

People have always designed things. One of the most basic characteristics of human beings is that they make a wide range of tools and other artefacts to suit their own purposes. As those purposes change, and as people reflect on the currently-available artefacts, so refinements are made to the artefacts, and sometimes

completely new kinds of artefacts are conceived and made. The world is therefore full of tools, utensils, machines, buildings, furniture, clothes, and many other things that human beings apparently need or want in order to make their lives better. Everything around us that is not a simple untouched piece of Nature has been designed by someone.

In traditional craft-based societies the conception or 'designing' of artefacts is not really separate from making them; that is to say, there is usually no prior activity of drawing or modelling before the activity of making the artefact. For example, a potter will make a pot by working directly with the clay, and without first making

any sketches or drawings of the pot. In modern industrial societies, however, the activities of designing and of making artefacts are usually quite separate. The process of making something cannot normally start before the process of designing it is complete.

In some cases- for example, in the electronics industry- the period of designing can take many months, whereas the average period of making each individual artefact might be measured only in hours or minutes.

Perhaps a way towards understanding this modern design activity is to begin at the end; to work backwards from the point where designing is finished and making can start. If making cannot start before designing is finished, then at least it is clear what the design process has to achieve. It has to provide a description of

the artefact that is to be made. In this design description, almost nothing is left to the discretion of those involved in the process of making the artefact; it is specified down to the most detailed dimensions, to the kinds of surface finishes, to the materials, their colours, and so on.

In a sense, perhaps, it does not matter how the designer works, so long as he or she produces that final description of the proposed artefact. When a client asks a designer for 'a design', that is what they want: the description. The focus of all design activities is that end-point.

Engineering Design Methods

Strategies for Product Design

THIRD EDITION

Nigel Cross

The Open University, Mi/ton Keynes, UK

JOHN WILEY & SONS, LTD

Chichester- New York. Weinheim • Brisbane. Singapore. Toronto