Lecture 5 concept appraisal and selection

4006ME Engineering Problem Solving

Concept Appraisal and Selection

Calendar

You Are Here

Today’s Session

• Today’s session will briefly present some concept selection and appraisal techniques, which can be used in your problem solving portfolio

• We will also discuss the requirements of CSWK1 due for submission on Friday 18th November 2011

Books for Reference

• Total Design – Integrated methods for successful product engineering

Stuart Pugh• Engineering Design

Rudolph J Eggert• Engineering Design Methods – Strategies

for product design

Nigel Cross

Books for Reference

• Strategies for Creative Problem Solving

H Scott Fogler, Steven E. LeBlanc

THE SCREENING PROCESSPart 1:

The Screening Process

• Before appraising possible concept solutions Eggert suggest the following screening questions should be asked to avoid wasting time:

Engineering Design – Rudolph J Eggert

Original Ideas

Screening Questions

Remaining Ideas


1. Will the concept be likely to function?

2. Will the concept likely meet the customers minimum performance requirements? (the ‘musts’ not the ‘should’)



3. Will the concept be likely to survive the operating environment?

4. Will the concept be likely to satisfy other critically important customer requirements?



5. Will you be able to manufacture the concept?

6. Will the concept satisfy financial and/or marketing requirements?


The Screening Process – Your Ideas


SORTING OUT IDEASPart 2:

Sorting Out Ideas

• Once the concept have been screened and any unsuitable concepts removed Pugh recommends the following steps.

Original Ideas

Screening Process

Remaining Ideas

Appraisal of Ideas

Sorting Out Ideas

1. It is essential that all ideas/solutions are related to the project design specification or statement.

2. Sketch each solution by hand to the same level of detail.

Total Design – Stuart Pugh

Sorting Out Ideas

3. Apply a concept selection and evaluation matrix.

4. It is essential that the matrix incorporates ‘visuals’ or sketches.


Sorting Out Ideas

5. Ensure that the comparison is valid – all concepts of same basis and to the same generic level of development.

6. Choose your evaluation criteria – these should be unambiguous, understood and accepted by all team members.


Sorting Out Ideas

7. Apply chosen evaluation matrix technique.

8. Assess individual scores of all the concepts. Certain concepts will have exceptional strengths, others will have exceptional weaknesses.


Sorting Out Ideas

9. Look at negatives in the strong concepts. What can be altered in the design to make it a positive?

10.Look at the weak concepts, attack the negatives to see if they can be improved upon.


Sorting Out Ideas

11. Having carried out steps 9 and 10 anything truly weak can now be eliminated.

12. If concepts do not converge its is usually an indication of the following:


Sorting Out Ideas

• Criteria are ambiguous and capable of interpretation by group members. Examination of criteria will reveal that it already incorporates one or more of the other criteria – decompose into a single one.

• Persistence of uniformity of strengths between concepts usually means that one or more concepts are subsets of others (they are the same)


Sorting Out Ideas

13. When one strong concept persists, re-run the matrix using this concept as the datum. Does the pattern persist? If it does this confirms the first run. If not repeat steps 9 and 10.


CONCEPT SELECTION METHOD – GO-CART TRANSMISSION EXAMPLE

Part 3:

Go-cart transmission example

CRITERIA CONCEPT ALTERNATIVES

GEARS V-BELT CHAIN

Σ +

Σ -

Σ S

DECIDE CRITERIA AND ENTER IN LEFT COLUMN



GEARS V-BELT CHAIN

HIGH EFFICIENCY

HIGH RELIABILITY

LOW MAINTENANCE

LOW COST

LIGHT WEIGHT

Σ +

Σ -

Σ SSELECT ONE CONCEPT AS DATUM DESIGN



GEARS V-BELT CHAIN

HIGH EFFICIENCY D

HIGH RELIABILITY A

LOW MAINTENANCE T

LOW COST U

LIGHT WEIGHT M

Σ + N/A

Σ - N/A

Σ S N/A

COMPARE EACH CONCEPT AGAINST THE DATUM USING ‘+’ ‘-’ OR ‘S’



GEARS V-BELT CHAIN

HIGH EFFICIENCY + D +

HIGH RELIABILITY + A +

LOW MAINTENANCE + T S

LOW COST - U -

LIGHT WEIGHT - M -

Σ + 3 N/A 2

Σ - 2 N/A 2

Σ S 0 N/A 1

Sum all the ‘+’

Sum all the ‘-’

Sum all the ‘S’



GEARS V-BELT CHAIN

HIGH EFFICIENCY + D +

HIGH RELIABILITY + A +

LOW MAINTENANCE + T S

LOW COST - U -

LIGHT WEIGHT - M -

Σ + 3 N/A 2

Σ - 2 N/A 2

Σ S 0 N/A 1

Can ‘-’ be turned into ‘+’??


• Results tallied, more +’s = strong design.• Can –’s be improved on.

• Major weakness – it gives all concepts an equal weighting.

Go-cart transmission example - modified


Importance (%)

GEARS V-BELT CHAIN

HIGH EFFICIENCY 30 + D +

HIGH RELIABILITY 25 + A +

LOW MAINTENANCE 20 + T S

LOW COST 15 - U -

LIGHT WEIGHT 10 - M -

100%

Σ + 75 N/A 55

Σ - 25 N/A 25

Σ S 0 N/A 20

Σ + = (1x30)+(1x25)+(1x20)

WEIGHTED RATING METHODPart 4

Weighted rating method

• Similar to modified concept selection method.

• Also called the weighted sum method or the Pahl and Beitz method.


1. Team selects evaluation criteria.

2. A matrix is prepared listing the evaluation criteria in the first column.

3. Importance weights given for criteria usually as percentage points, adding to 100.

Weighted rating method – Go-cart transmission

Concept Alternatives

Gears V-belt Chain

Criteria Importance Weight (%)

Rating Weighted rating



High Efficiency

30

High Reliability

25

Low Maintenance

20

Low Cost 15

Light Weight 10

Totals 100


4. Concepts identified in columns.

5. Team rates each concept as:

Unsatisfactory 0

Just tolerable 1

Adequate 2

Good 3

Very Good 4



Gears V-belt Chain





High Efficiency

30 4 2 3

High Reliability

25 4 3 3

Low Maintenance

20 4 3 2

Low Cost 15 2 4 3

Light Weight 10 2 4 3

Totals 100


6. Each concept rating is multiplied by its respective weight and summed to produce an overall rating for the concept.

7. Strong concepts are achieve higher scores.



Gears V-belt Chain





High Efficiency

30 4 1.20 2 0.60 3 0.90

High Reliability

25 4 1.00 3 0.75 3 0.75

Low Maintenance

20 4 0.80 3 0.60 2 0.40

Low Cost 15 2 0.30 4 0.60 3 0.45

Light Weight 10 2 0.20 4 0.40 3 0.30

Totals 100 3.50 2.95 2.80


• Problems – the method is subjective, fuzzy and abstract.

• Positives – designs for further development will be identified and it allows teams to reach a consensus.

PROBLEM SOLVING PORTFOLIO

Part 5:

Problem Solving portfolio

• 18 Nov 2011 - Your coursework should be submitted in two ways:

• A physical copy should be handed in via the campus centre.

• An electronic version should be created using your group Wiki tool on blackboard. It is very important that each person enters their individual work to allow for the assessment of individual contribution to the portfolio.

Problem Solving portfolio

• Feedback will be given when your coursework is returned to you within three weeks of submission.

FINALLY

Lecture 5 concept appraisal and selection

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