chapter 1 introduction to mechanical design process

7/26/2019 Chapter 1 Introduction to Mechanical Design Process

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MECHANICAL ENGINEERING DESIGN 1

MEC 531

PART A

MECHANICAL DESIGN PROCESS

By:

NURZAKI IKHSAN


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Chapter Outline

1. The Phases of Design

2. Problem identification and definition3. Product design specifications

4. Concept development, evaluation and selection

CHAPTER 1INTRODUCTION TO MECHANICAL

DESIGN PROCESS


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The Phase Of Design

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

process.

What is Design?

To survive!

As an engineer as technical provider, we provide solutions to particular problems

However -if clients are not completely satisfied with provider then they will dismiss

They will go somewhere else and tell everyone about the unsatisfactory

Why do we design ?


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The Phase Of Design

7 Phases Design Process

Phase I.

Conceptual

Design

Phase II.

Embodiment

Design

Phase III.Detail Design

Phase IV.

Planning for

Manufacture

Phase VII.

Planning for

Retirement

Phase VI.

Planning for

Use

Phase V.

Planning for

Distribution

Define

Problem

Parametric

Design

Configuration

Design

Product

Architecture

Evaluation of

Concepts

Concept

Generation

Gather

Information


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The Phase Of Design


Phase I.

Conceptual

Design

Define

Problem

Evaluation of

Concepts

Concept

Generation

Gather

Information

Feasibility Study.

Requires greatest creativity, involves the most

uncertainty and requires coordination among many

functions in the business organization.

Discrete activities to be considered:

Identification of customer needs

Problem definition

Gathering information

Conceptualization

Concept selection

Design review


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The Phase Of Design


Phase I.

Conceptual

Design

Define

Problem

Evaluation of

Concepts

Concept

Generation

Gather

Information

Most important steps in the engineering design

process is identifying customer needs.

The customer needs can be gained from:

Interviewing customers

Focus groupCustomer survey

Customer complaints

Tools to achieve this:

Benchmarking

QFD

PDS


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The Phase Of Design


Phase I.

Conceptual

Design

Define

Problem

Evaluation of

Concepts

Concept

Generation

Gather

Information

Information from Internet

Engineering URLs

Patent Literature

Intellectual Property

Patents

Handbook


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The Phase Of Design


Phase I.

Conceptual

Design

Define

Problem

Evaluation of

Concepts

Concept

Generation

Gather

Information

Brainstorming

Functional decomposition

Morphological chart


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The Phase Of Design


Phase I.

Conceptual

Design

Define

Problem

Evaluation of

Concepts

Concept

Generation

Gather

Information

Comparison Based on Absolute Criteria

Pughs Concept Selection Method

Weighted Decision Matrix


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The Phase Of Design


Phase II.

Embodiment

Design

Parametric

Design

Configuration

Design

Product

Architecture

Preliminary Design.

Decisions are made in this design phase: strength,

material selection, size, shape, and spatial compatibility.

Any major changes beyond this design phase become

very expensive.


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The Phase Of Design


Phase II.

Embodiment

Design

Parametric

Design

Configuration

Design

Product

Architecture

Arrangement of the physical elements to carry out its

required function.

i.e. defining the building blocks of the product in terms of

what they do and their interfaces

Design for Human Factor

Creating user-friendly Design


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The Phase Of Design


Phase II.

Embodiment

Design

Parametric

Design

Configuration

Design

Product

Architecture

Establishing the shape and general dimensions of the

components.

Components include special purpose parts, standard

parts, standard assemblies or modules.

Develop from function.

Configuration depending on:

1. Available materials and production methods

2. Spatial constraints3. Product architecture


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The Phase Of Design


Phase II.

Embodiment

Design

Parametric

Design

Configuration

Design

Product

Architecture

Set the dimensions and tolerances in order to maximize

quality and performance and minimize cost.

Objective : to set values for the design variables that

will produce the best possible design considering bothperformance and manufacturability.

A few established method in designing to maximise

performance and quality :

FMEADesign for reliability

Robust design

Design for Assembly (DFA)

Design for Manufacture (DFM)


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The Phase Of Design


Phase III.Detail Design

Final Phase- Detail design

Waiting for final decision to be manufacture

The design is brought to the stage of a

complete engineering description of a tested

and producible product.

Any missing or incomplete information are added

arrangement, form, dimensions, tolerances,

surface properties, materials and manufacturing of

each part

Activities to be completed in the detail design

phase (documentation):

Detail engineering drawing.

Verification testing of prototype.

Assembly drawings and instruction, BOM.A detailed product specification.

Decisions either to fabricate each part or to buy it

A detailed cost estimation.

A design review as a conclusion of the detail

design phase before beingpassed to manufacturing.


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The Phase Of Design


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A document that contains all of the facts related to the outcome of

the product development (document listing the problem in detail).

It should avoid forcing the design direction toward a particular

concept and predicting the outcome.

Should be understood that the PDS is evolutionary and will change

as the design process proceeds.

It is important to work with the customer and analyse the

marketplace to produce a list of requirements necessary to

produce a successful product. The designer should constantly refer back to this document to

ensure designs are appropriate.

Product Design Specifications (PDS)


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Example: PDS

1. What is the product going to be?

2. What are the dimensions of the product?

3. What materials does the product require?

4. What is the estimate cost of the materials?

5. What tools/technology will be used to work on the project?

6. Are the tools/technology accessible, or will special arrangements need to be made?

7. What is the time estimate for completing the project?

8. Where will the product be worked on primarily?

9. Will an outside company be used to complete the project?

10. Will materials need to be ordered? If so, how much time should be allotted for

shipping, ordering, etc?

11. Will an expert in the field need to assist with the creation of the product? If so,

when will this person be contacted to set up a mutually convenient time to meet?

12. Who will benefit from the benefit from the creation of the product?

13. Why is it necessary to create this product?

14. How will the product demonstrate technical knowledge?



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PRODUCT DESIGN SPECIFICATION

Product: Lightweight wheel for Formula Student car.

Weight :Maximum 3kg

Size :13 diameter;

15-25mm centre thicknessTimescale :18 weeks from initial phase to manufacture.

Cost :Maximum RM300 per wheel

Quantity :4 on initial design run

Safety :-Design for fatigue life of 250000 cycles at approximately

1.4g loading-Interface between centre and rims must be airtight

-Smooth surface finish

-Secure fittings



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Competition :There are few competitors in niche market, butvarious racing wheel manufacturers.

Maintenance :Seals and bolts must be checked occasionally.

Customer :Lightweight motorsport / weekend racer.

Manufacturing Facilities :Dependent upon material

CNC and Casting in-house.Other manufacturing must be out-sourced.

Installation :4 inch PCD 4 stud formation.

Materials :Range of materials to be modelled:

Aluminium 2024 T6

Steel

Plastics



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Generating Design Concepts

Brainstorming

Most common method used by design teams for generating ideas for design

concepts in conceptual design.

Think of all the possible limitations or shortcomings of the product.

Functional decomposition (breakdown)

A logical approach for describing the transformation between the initial and final

states of a system or device.

Physical decomposition separating the product or subassembly directly into its

subsidiary subassemblies and components (output = physical decomposition block

diagram).

Functional decomposition a general description of a device is refined into more

specific arrangements of functions and subfunctions.

Concept Development, Evaluation and Selection


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Urban Car

Suspensionsystem

Steeringsystem

ChassisBrakingsystem

Power train

Power train

Variable valvetiming

The controller are use tovaries the operational of the

open-closed valve

Direct injection

The gasoline is highly pressurized, andinjected via a common rail fuel line

directly into the combustion chamber

3.5 cc

The engine consist of 6pistons

Physical decomposition

Functional decomposition


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Morphological chart

Representing and exploring all the relationships in multidimensional problems

regarding shape and form



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Concept Evaluation & Selection

Evaluation methods:

1. Pugh concept selection method.

2. Weighted decision matrix.



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Pugh Concept Selection Method

This method compares each concept relative to a reference or datum concept.

Each criterion determines whether the concept is better than, poorer than or about

the same as the reference concept.

Steps in this Pugh concept selection method:

1. Choose the criteria by which the concepts will be evaluated

- Can refer to QFD (House of Quality).

2. Formulate the decision matrix

- Concepts on the row headings and criteria on the column headings.3. Clarify the design concepts

- Make sure every team member understand every concept developed.



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4. Choose the datum concept

- Reference concept with which all other concepts are compared.

5. Run the matrix

- Use a three-level scale, better (+), worse (-) or same (S).

6. Evaluate the ratings

- Sum up the +, - and S ratings.

7. Establish a new datum and rerun the matrix

- To gain added insight regarding the highest rated concept.

8. Examine the selected concept for improvement opportunities

- Is there any improvement that can be done considering the worse ratings gained forthe selected concept.



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Weighted Decision Matrix

Evaluating competing concepts by ranking the design criteria with weighting factors

and scoring the degree to which each design concept meets the criterion.

Weighting factors:

- A 5-point scale (0-4) knowledge of the criteria is not very detailed.

- An 11-point scale (0-10) the information is more detail.

The evaluation steps are quite similar to Pugh concept selection method but without

any datum.



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chapter 1 introduction to mechanical design process

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