chapter 1 introduction to mechanical design process
TRANSCRIPT
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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
7 Phases Design Process
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
7 Phases Design Process
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
7 Phases Design Process
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
7 Phases Design Process
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
7 Phases Design Process
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
7 Phases Design Process
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
7 Phases Design Process
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
7 Phases Design Process
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
7 Phases Design Process
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
7 Phases Design Process
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?
Product Design Specifications (PDS)
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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
Product Design Specifications (PDS)
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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
Product Design Specifications (PDS)
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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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Concept Development, Evaluation and Selection
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
Concept Development, Evaluation and Selection
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Concept Evaluation & Selection
Evaluation methods:
1. Pugh concept selection method.
2. Weighted decision matrix.
Concept Development, Evaluation and Selection
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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.
Concept Development, Evaluation and Selection
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Concept Development, Evaluation and Selection
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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.
Concept Development, Evaluation and Selection
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Concept Development, Evaluation and Selection