The Design Process & The Role of CAD

7/27/2019 The Design Process & The Role of CAD

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CHAPTER 3 (a)

The Design Process &

The Role of CAD

MEC435

COMPUTER-AIDED DESIGN

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3.1 DESIGN PROCESS

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• Any product begins with a

need based on customers’

and markets’ demand

before being translated into

a finished product.

• Main processes involve:

– Design process.

– Manufacturing process.



Types of Design

• Original Design

– Also called innovative design.

– A truly original design involves invention.

– Successful original design rarely occur, but when they do occur they will give a

big impact to the market.

– E.g. Microprocessor.

• Adaptive Design

– Adapts a design from a known solution to fulfill a different need to produce a

novel application.

– Involves synthesis and are relatively common in design.

– E.g. Adapting the ink-jet printing concept to spray binder to hold particles in place

in a RP machine.

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• Redesign

– Mostly practiced to improve an existing design.

– Usually does not involve the change in the working principle or concept if the

original design.

– Maybe changing some of the design parameters (e.g. materials, shape, etc.) →

variant design.

• Selection Design

– Most design uses standards components supplied by vendors.

– Implemented by selecting certain components base on the needed performance,

quality and cost from catalogs of potential vendors.

• Industrial Design

– Deals with improving the appeal of a product to the human senses especially its

visual appeal (aesthetic).

– More artistic than engineering but still an important aspect of kinds of design.

– Consideration on how the human user can best interface with the product.

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Closed-loop Product Cycle

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Product Cycle in Conventional Manufacturing Environment



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Product Cycle in Computerized Manufacturing Environment

Morphology of Design

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Phase 1: Conceptual Design

Phase 2: Embodiment Design

Phase 3: Detail Design

Phase 4: Planning for Manufacture

Phase 5: Planning for Distribution

Phase 6: Planning for Use

Phase 7: Planning for Retirement of product



Engineering Design Process 1st Three Phases

Define problemProblem

statement

Benchmarking

QFD

PDS

Project planning

Gatherinformation

Internet

Patent

Technical articles

Trade journal

Consultants

Concept

generationCreativity

methods

Brainstorming

Functional models

Decomposition

Systematic design

methods

Evaluate & selectconcept

Decision making

Selection criteria

Pugh chart

Decision matrix

AHP

Product

architecture

Arrangement of

physical elements

Modularity

Configuration

design

Preliminary

selection of

materials andmanufacturingprocess

Modeling

Sizing of parts

Parametric design

Robust design

Set tolerance

DFM,DFA,DFETolerances

Detail design

Engineering

drawingsFinalize PDS

Phase 1- conceptual design

Phase 2- embodiment design9

Phase 3- detail design

PRINCIPLES OF DFMA

• Minimize total number of parts

• Use modular design

• Minimize part variations

• Use a multifunctional design

• Design parts for multiuse

• Design to simplify fabrication

• Use of fastener

• Minimize assembly direction

• Maximize compliance• Minimize handling

• Eliminate or simplify adjustment

• Avoid flexible component

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Design For Manufacture (DFM)

• Design for ease of manufacture of the collection of parts

or product

• More as a philosophy

• It is a way of thinking that can be applied to component

or product

• DFM 3 key element:

1. Process selection

2. Reducing the number of process stages

3. Designing of the process

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1. Process Selection

• Analysis of material and processing methods for

individual component based on:

- Tolerance requirement

- Production volume

- Component complexity requirement

- Critical performance criteria

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2. Reducing Process Stages

• Eliminate unnecessary process stages through:

- Component minimization

- Elimination of finishing process

- Combining processes

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3. Design of the Process

• To ensure design of component will satisfy the specific

production process

• Exploit the benefits and limitation of the process

- Design for machining

- Design for casting

- Design for injection moulding

- Design for Powder Metallurgy

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Design for Assembly (DFA)

• Simplicity – minimize part number, part variety, simplifyassembly sequences and component handling andinsertion

• Standardize – on material usage

• Use the widest possible tolerance

• Choose material that suit function and productionprocess

• Minimize non value added operations

• Team work

• Reduce number of parts• Ensure that the remaining parts are easy to assemble

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Design for Assembly Outcomes

• Shorten product design time

• Reduce assembly time

• Simplify assembly process

• Reduce total material cost

• Improves quality and reduce defects

• Reduce labour content

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OTHER DESIGN

CONSIDERATIONS

1. Product Use

2. Design Life

3. Human Factor Consideration

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1. Product Use• “Customer is always right”

• U.S. consumer products are developed under a philosophy that the

customer will buy the cheapest product available.

• But it is hopefully not as true for engineering design products where

the customer is more sophisticated and will normally demand

performance, reliability, serviceability, reasonable cost, safe

operation, and good human engineering (ergonomics).

• Customer expectations are compared with the various product

design characteristics to identify those that are not addressed and

to develop an optimized product plan incorporating design

modifications accommodating the dominant expectations.

• Product liability in the United States is a design consideration that

is growing in importance.

• Users of products are increasingly aware of their opportunities to

sue manufacturers, and court sentiment often leans toward the

consumer even when product misuse is involved. 18



2. Design Life

• Many engineering design products are designed for a specific

installation or assembly, and it is normally assumed that they will

remain in this application for their useful life.

• Design life is in terms of cycles or hours of operation, and it is a

fairly straightforward task to design and test the product to meet

these requirements.

• Some thought needs to be given to retirement of the product after

completion of its design life.

• If the environment is to be treated as surroundings (in a

thermodynamic context), the product must be capable of being

refurbished and reused or the materials of construction must be

recyclable or biodegradable.

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3. Human Factor Consideration• All designers should consider the operator of the device,

component, or system under development and strive to produce

user-friendly products.

• The term operator must include the person(s) that maintains and

repairs the product as well as the person that uses it.

• A significant amount of anthropomorphic information is available

that can be used to determine the size and location of manually

actuated devices on the product as well as the optimum location of

visual elements.

• An individual's capacity for doing work should be considered in the

design and, for repetitious tasks, a system layout should be

selected that minimizes boredom but does not overload the

individual's capacity to comprehend.

• The product must be aesthetically appealing because many

products are purchased primarily due to their look and may be the

feature that initially interests the potential buyer. 20



3.2 COMPUTER APPLICATIONS

• Three (3) major computer applications in engineering environment.

1. Design

2. Analysis

3. Manufacturing

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Computer Application in Design

• Conceptual and also geometrical modeling design stage uses a lot

of computer application.

• Both hardware and software.

• Visualizing and styling of products for concept generation → 1st idea

of product.

• Widely usage of CAD tools → graphics and 3D modeling.

• E.g. Hardware: 3D Scanner, digitizer, pointing device etc.

• E.g. Software: AutoCAD, Pro-Engineer, Solidworks, UniGraphics,

CATIA etc.

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Computer Application in Analysis

• Engineering analysis and optimization design stage uses computer

application.

• Mainly for design analysis → structure, strength, heat transfer, fluid

flow etc.

• Analysis may be used as a source of design verifications for design

calculations and predictions.

• Involves CAE tools → FEA, CFD, Ergonomics etc.

• E.g. ABAQUS, ANSYS, Mannequin-Pro, CFX etc.

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Computer Application in Manufacturing

• Mainly used for planning, monitoring, control and executing

manufacturing processes.

• Use of CAM tools → CNC machines, software etc.

• Involves wide areas from process planning to marketing.

• E.g. Software: MasterCAM

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The Design Process & The Role of CAD