What is design? 이대길 KAIST 기계공학과 교수 한국과학기술한림원 정회원 한국복합재료학회 부회장

Mechanical Design Lab. with Advanced MaterialsMechanical Design Lab. with Advanced Materials

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What is design?

이대길

KAIST 기계공학과 교수

한국과학기술한림원 정회원

한국복합재료학회 부회장


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1. Normal design processes

2. Motorola’s 6 Program

3. Axiomatic design process

Contents:


3

1. Normal design processes

Ref. J. E. Shigley, C. R. Mischke and R. G. Budynas, Mechanical Engineering Design, 7th Edition, McGraw Hill, 2003


4What is engineering?What is engineering?

Engineering= Design + Manufacturing


5

Design is an interplay between

what we want to achieve and

how we want to achieve it.

What is design?What is design?


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The designers (mechanical engineer, electrical engineer, mayor, CEO, etc) must do the following.

1. Know or understand their customers’ needs.

2. Define the problem they must solve to satisfy the needs.

3. Conceptualize the solution through synthesis.

4. Perform analysis to optimize the proposed solution (Adequacy assessment).

5. Check the resulting design solution to see if it meets the original customer needs.

What is design?What is design?


7What is design?What is design?


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Design product should be

1.Functional: satisfy the intended need and customer expectation.

2. Safe: not hazardous to the user, bystanders, or surrounding property with appropriate directions or warnings provided.

3. Reliable: perform its intended function satisfactorily or without failure at a given age.

4. Competitive: product survival.

Adequacy of DesignAdequacy of Design


9Adequacy of Design-continuedAdequacy of Design-continued

Design product should be

5. Usable: user friendly product.

6. Manufacturable: suited to mass production with a minimum number of parts (or information).

7. Marketable: purchasable with repair available.


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1. Functionality 2. Strength/stress 3. Distortion/deflection/stiffness.

4. Wear 5. Corrosion 6. Safety

7. Reliability 8. Manufacturability 9. Utility (electricity, gas. etc)

10. Cost 11. Friction 12. Weight

13. Life 14. Noise 15. Styling

16. Shape 17. Size 18. Control

19. Thermal Properties 20. Surface 21. Lubrication

22. Marketability 23. Maintenance 24. Volume

25. Liability 26. Remanufacturing/resource recovery

Interaction between Design Process Interaction between Design Process ElementsElements


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Computational Tools CAD (Computer-aided design) software:

Aries, AutoCAD, CadKey, I-deas/Unigraphics, ProEngineer, etc.

CAE (Computer-aided engineering):

Finite element analysis/method (FEA or FEM):

Algor, ANSYS, MSC/NASTRAN, ABAQUS, etc.

Computational fluid dynamics:

CFD++, FIDAP, Fluent, etc.

Dynamic force and motion in mechanics:

ADAMS, DADS, Working Model, etc.

Acquiring Technical Information Libraries, Government sources, Professional societies, commercial vendors, internet and TRIZ.

Design Tools and ResourcesDesign Tools and Resources


12Design Engineer’s Professional Responsibilities• Satisfy the needs of customers (management, clients, consumers, etc.).

• Communicate your ideas clearly and concisely, or your technical proficiency may be compromised.

• The design engineer’s professional obligations include conducting activities in an ethical manner. (There’s no engineers in the hell).

Engineer’s Creed from the National Society of Professional Engineers (NSPE).


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Standard: a set of specifications for parts, materials, or processes intended to achieve uniformity, efficiency, and a specified quality.

Code: a set of specifications for the analysis, design, manufacture, and construction of something.

All of the organizations and societies have established specifications for standards and safety or design codes.

AA, AGMA, AISC, AISI, ANSI, ASM, ASME, ASTM, AWS, ABMA, BSI, IFI,

I. Mech. E., BIPM, ISO , NIST, SAE, JIS, DIN

Codes andCodes andStandardsStandards


14Economics

• Standard sizes

• Large tolerances

• Breakeven points

• Cost estimates (cost per weight, number of parts, area, volume, horsepower, torque, capacity, speed and various performance ratios).


15Safety and Product Liability

• The strict liability concept of product liability generally prevails in the United States.

• The manufacturer of an article is liable for any damage or harm that results because of a defect. It does not matter whether the manufacturer knew about the defect, or even could have known about it.


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The reliability method of design is one in which we obtain the distributions of stresses and the distribution of strengths and then relate these two in order to achieve an acceptable success rate.

Reliability


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Should an automotive engineer increase the cost per car by 10,000 Won in order to avoid 100 failures in a production run of a million cars, where the failure would not involve safety, but would entail a 100,000 Won repair?

Reliability


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Should 10 billion Won be spent to save 10 million Won plus some customer inconvenience?

6=1/109

Reliability


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The 6 quality is a phrase made famous by Motorola once it decided to refocus on quality in the late 1970s and early 1980s.

It is a quality assurance program that has the goal of reducing the defective parts in a bath to as low as 3.4 parts per million (106).

A rigorous interpretation of 6 is really 2 defects per billion parts (109) made.

If we consider each side of center, then 6.8 components per million will lie in the tails with 3.4 on each side.

5.4


21Motorola’s 6 s Program


22Motorola’s 6 ProgramWhen the center of the normal distribution curve drifts by 1.5 to the right, and is viewed still window, there will be virtually no defects in the left-side tail but a rather large number in the right-side tail (1350 parts per million).

If we view with the window of , the right tail contains 3.4 parts per million, with negligible number of parts in the left signal.

There is an infinite combination of “m offset plus n viewing window” for quality performance of 3.4 parts per million.

The number of 3.4 parts per million is used as the bench mark rather than the rigorous definition of 6.

0.6

5.4


23Calculations and Significant Figures• Usually three or four significant figures are

necessary for engineering accuracy.

• Make all calculations to the greatest accuracy possible and reports the results within the accuracy of the given input.


24Calculations and Significant Figures

• To display 706 to four significant figures: 706.0, 7.060 10ⅹ 2, 0.7060 10ⅹ 3

• To display 91600 to four significant figures: 91.60 10ⅹ 3

• When d=0.40 in d=3.1(0.40)=1.24in=1.2 in d=3.141592(0.40)=1.256in=1.3 in


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3. Axiomatic design process


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References:

1. Dai Gil Lee and Nam P. Suh, Axiomatic Design and Fabrication of Composite Structures, Oxford University Press, August, 2005.

2. Nam P. Suh, Axiomatic Design, Oxford University Press, 2000.

3. Nam P. Suh, The Principles of Design, Oxford University Press, 1990.

Introduction to Axiomatic Design


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▪ There are several key concepts that are fundamental to axiomatic design.

▪ They are the existence of domains, mapping, axioms, and decomposition by zigzagging between the domains, theorems, and corollaries.



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Customer domain

Functional domain

Physical domain

Process domain

{CAs} {FRs} {DPs} {PVs}

mapping mapping mapping



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▪ The customer domain is characterized by the needs (or attributes) that the customer is looking for in a product or process or system or material. ▪ In the functional domain, the customer needs are specified in terms of functional requirements (FRs) and constraints (Cs). ▪ In order to satisfy the specified FRs, we conceive design parameters (DPs) in the physical domain.▪ Finally, to produce the product specified in terms of DPs, we develop a process that is characterized by process variables (PVs) in the process domain.

Key Concepts of Axiomatic Design Theory


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Once we identify and define the perceived customer needs, these needs must be translated to FRs.

This must be done within a "solution-neutral environment." without ever thinking about existing products or what has been already designed or what the design solution should be (Japanese method).

Often designers and engineers identify solutions first by looking at existing materials or products before they define FRs, which leads to a description of what exists rather what is needed.



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Axiom 1: The Independence Axiom Maintain the independence of the functional requir

ements (FRs).

Axiom 2: The Information Axiom Minimize the information content of the design.

TWO AXIOMSTWO AXIOMS


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Independence Axiom:

FRs are defined as the minimum set of independent requirements that characterize the design goals.

▪ Information Axiom:

The design that has the smallest information content is the best design.

1.3 Key Concepts of Axiomatic Design Theory


33Knob Design for a Shaft

FR1=Grasp the end of the shaft tightly with axial force of 30 N

FR2=Turn the shaft by applying 15 N-m of torque

DP1=Interference fit between the shaft and the inside diameter of the knob

DP2=The flat surface

2

1

2

1

DP

DP

Xx

XX

FR

FR


34Knob Design for a ShaftFR1=Grasp the end of the shaft tightly with axial force of 30 N

FR2=Turn the shaft by applying 15 N-m of torque

DP1=Interference fit between the shaft and the inside diameter of the knob

DP2=The flat surface

2

1

2

1

0

0

DP

DP

X

X

FR

FR


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Bias

Probability density

System pdf

Area within common range (Acr)

Variation from the peak value

Target

Design range

PlogP

logI ii

i 221


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Information content Ii for a given FRi is defined

in terms of the probability Pi of satisfying FRi.

PP

I i

i

i 22 log1

log

(1.6)


The probability is determined by the overlap between the design range and the system range.


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▪ The design that has the highest probability of success is the best design.

▪ In an ideal design, the information content should be zero to satisfy the FR every time and all the time.

▪ The design goals are often subject to constraints (Cs). Constraints provide bounds on the acceptable design solutions and differ from the FRs in that they do not have to be independent.



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FRs and DPs (as well as PVs) must be decomposed to the leaf-level until we create a hierarchy.

From an FR in the functional domain, we go to the physical domain to conceptualize a design and determine its corresponding DP.

Then, we come back to the functional domain to create FR1 and FR2 at the next level that collectively satisfies the highest-level FR.



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FR1 and FR2 are the FRs for the highest level DP.

Then we go to the physical domain to find DP1 and DP2 by conceptualizing a design at this level, which satisfies FR1 and FR2, respectively.


FR

FR1

FR11

FR121

FR12

FR122FR123

FR1231 FR1232

FR2

Functional domain

DP

DP1

DP11

DP121

DP12

DP122DP123

DP1231 DP1232

DP2

Physical domain


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FR

FR1

FR11

FR121

FR12

FR122FR123

FR1231 FR1232

FR2

Functional domain

DP

DP1

DP11

DP121

DP12

DP122DP123

DP1231 DP1232

DP2

Physical domain


This process of decomposition is continued until the FR can be satisfied without further decomposition when all of the branches reach the final state. The final state is indicated by thick boxes, which is called a “leaf” or “leaves”.


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DPs:DP1 = Vertically hung door

DP2 = Thermal insulation material

2

1

2

1

DP

DP0

FR

FR

XX

X

FRs: FR1= provide access to the food in the refrigerator .FR2= minimize energy consumption



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Bend a titanium tube to prescribed curvatures maintaining the circular cross section of the bent tube.

Titanium has a hexagonal close packed (hcp) structure so that its mechanical properties anisotropic, and it cannot be bent repeatedly because it will fracture.

Design Example

FR1 = Bend a titanium tube to prescribed curvatures.FR2 = Maintain the circular cross section of the bent tube.


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Fixed set of counter-rotatinggrooved feed rollers

Flexible set of counter-rotating grooved rollersfor bending

Pivotaxis

1 = 2

1 > 2

1

2

1

2

Tube betweenthe two bending rollers

DP1 = Differential rotation of the bending rollers to bend the tube DP2 = The profile of the grooves on the periphery of the bending

rollers


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Design rangepdf

Target

System pdf

90 110 100 c m FR (Length, cm)

To cut Rod A to 1 10-6 m and Rod B to 1 0.1m. Which has a higher probability of success?

Cutting a Rod


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FR1 = Commuting time must be in the range of 15 to 30

minutes.

FR2 = The quality of the high school must be good, i.e., more

than 65 % of the high school graduates must go to reputable colleges.

FR3 = The quality of air must be good over 340 days a year.

FR4 = The price of the house must be reasonable, i.e., a four

bedroom house with 3000 square feet of heated space must be less than $ 650,000.

Buying a houseBuying a house


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FR1 = Commuting time must be in the range of 15 to 30 minutes.

FR2 = The quality of the high school must be good, i.e., more than 65 % of

the high school graduates must go to reputable colleges.FR3 = The quality of air must be good over 340 days a year.

FR4 = The price of the house must be reasonable, i.e., a four bedroom

house with 3000 square feet of heated space must be less than $ 650,000.

FR1 =

Commute

FR2 = Quality FR3 = Quality FR4 = Price

Town Time [min] of schools [%] of air [days] [1000 $]

A 20 to 40 50 to 70 300 to 320 450 to 550

B 20 to 30 50 to 75 340 to 350 450 to 650

C 20 to 45 50 to 80 350 and up 600 to 800

Town I1 (bits) I2 (bits) I3 (bits) I4 (bits) I (bits)

A 1.0 2.0 Infinite 0 Infinite

B 0 1.32 0 0 1.32

C 2.0 1.0 0 2.0 5.0

Buying a houseBuying a house


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K=stiffness

1FR

FR

DPDP

DP

Estimating the height of Washington Monument

Students were asked to estimate the height of the George Washington Monument.

They were given tape measures that can measure the length of the shadow of the monument accurately.

Then they were asked to eyeball the angle from the end of the shadow to the top of the monument.

Which will give the closer height when it was measured at 1 P.M. and 5 P.M.?


48Hot and Cold Water Faucet

2

1

XX

XX

T

Q


49Hot and Cold Water Faucet

2

1

0

X

xX

T

Q


50Van Seat Assembly


51Design Failure Examples-Challenger Space Shuttle

The solid rocket booster segments are joined by a tang-and-clevis arrangement, with two O-rings to seal the joint and 177 steel pins around the circumference to hold the joint together. The zinc chromate putty acts as an insulation that under pressure would behave plastically and move toward the O-rings.


52Design Failure Examples -Cubicle Failure

A large open area with a high ceiling was to be heated and cooled with three cubical units, each suspended from the ceiling by long steel rods (S.F.=17) at four corners.

The cubicles were being fitted with heat exchangers, blowers, and filters by workers inside and on top of the enclosures.

The flexibility of the long support rods permitted the cubicles to swing back and forth, and the workers sometimes enjoyed getting their cubicles swinging with considerable amplitude, Fatigue failure of a support rod caused the death of one worker.


53Design Failure Examples-Press Accident

A worker lost a hand in a 400-ton punch press

despite wearing safety cuffs that were cam-actuated

to pull the hands.

The cause was a loosened setscrew, which delayed

the hand retraction until after the ram came down.


54Design Failure Examples- Engine Cover FailureWhen the joint is not separated

P=Pb+Pm

=Pb/kb=Pm/km=P/(kb+km)

Pb=CP

C=kb/(kb+km)

The resultant bolt force is

Fb=Pb+Fi=CP+Fi

Fm= -kmP/(kb+km)+Fi=-(1-C)P+Fi

Documents

What is design? 이대길 KAIST 기계공학과 교수 한국과학기술한림원 정회원 한국복합재료학회 부회장