Optimization and Trade-Off Analysis
Home ENSE 621 Project ENSE 621 Homework Christine's Page Lance's Page

 

Optimization and Trade-Off Analysis

 A design survey was used in order to rate the importance of the design criteria presented earlier.  The survey consisted 19 individuals from Grove Worldwide who work in Marketing, Design Engineering, and Manufacturing Engineering.  The individuals’ positions included management and engineers.  The design survey is shown below.

Design Survey

 Please take the time to rate the following design criteria for a cab frame design – cab frame consisting of the outer shell of the cab.  The criteria should be rated on a scale from 1 to 4, 1 being of highest importance.  There are no right or wrong answers.  This information will be used for an optimization analysis for a systems engineering project.  Thank you for your input.

 Rate the following Criteria:

Appearance - Does the product look aesthetically pleasing?  Does the product appear to meet the design requirements?  Does the product look modern?

Cost – Tooling, material, manufacturing, etc.

Functionality – Does this product satisfy the design requirements and standards, i.e. last the lifetime of the product, provide shelter from the elements…

Time-to-Market – Examples:  ease of making changes to the design, ease of manufacture, time required to build prototypes and pilots, time required to build production units

  The results of the survey are summarized in the following table.

Table 1

Criteria Ranking

Ranking

1

2

3

4

Evaluation Criteria

Appearance

 

II

IIII II

IIII IIII

Cost

I

IIII IIII IIII

II

I

Functionality

IIII IIII IIII II

I

 

I

Time-To-Market

I

I

IIII IIII

IIII II

The survey results were used to estimate a weighting factor for each criterion.  This is basically equivalent to a probability factor.  First, a weighted score was calculated for each criterion by taking the number of each ranking times the rank and adding all values.  (In this calculation, in order for a rank of 1 to be of highest important, rank 1 was given a value of 4, rank 2 was given a value of 3, etc.)  The weighting factor was then calculated by dividing the weighted score by the total of all weighted scores.  Shown below is a sample calculation for appearance.

 

 The calculated weighting factors are shown for each evaluation criteria in the table below.

Table 2

Weighting

Evaluation Criteria

Appearance

Cost

Functionality

Time-to-Market

Weighted Score

30

54

72

34

Weighting Factor

.16

.28

.38

.18

A decision table was used to evaluate each manufacturing method with respect to the criteria.  Cost and time-to-market was ranked according raw data received from Design Engineering.  Appearance and functionality are somewhat subjective and were ranked by an engineer involved with the project.  The decision table is shown below.

Table 3

Decision Table

Evaluation Criteria

Appearance

Cost

Functionality

Time-To-Market

Alternatives

Mechanical Fasteners

4

3

2

1

Welding

3

2

1

1

Structural Adhesive

2

1

1

1

Molded Fiberglass

1

4

1

2

 With the rank and weighting factor known, the weighted rank is calculated as shown in the table below. 

Table 4  Weighted Rank Calculation
 
Manufacturing method = Mechanical Fasteners
Evaluation Criteria

Weighting Factor

Engineering Rank

Weighted Rank

Appearance

           .16

4

             .64

Cost

           .28

2

             .56

Functionality

           .38

3

           1.14

Time-to-Market

           .18

1

             .18

Totals

         1.00

 

           2.52

 
Manufacturing method = Welding
Evaluation Criteria

Weighting Factor

Engineering Rank

Weighted Rank

Appearance

           .16

3

             .48

Cost

           .28

2

             .56

Functionality

           .38

1

             .38

Time-to-Market

           .18

1

             .18

Totals

         1.00

 

           1.60

 
Manufacturing method = Structural Adhesive
Evaluation Criteria

Weighting Factor

Engineering Rank

Weighted Rank

Appearance

           .16

2

             .32

Cost

           .28

1

             .28

Functionality

           .38

1

             .38

Time-to-Market

           .18

1

             .18

Totals

         1.00

 

           1.16

 
Manufacturing method = Molded Fiberglass
Evaluation Criteria

Weighting Factor

Engineering Rank

Weighted Rank

Appearance

           .16

1

             .16

Cost

           .28

4

          .1.12

Functionality

           .38

1

             .38

Time-to-Market

           .18

2

             .36

Totals

         1.00

 

           2.02

 

As one can see from Table 4, using structural adhesives is the optimal choice for the cab frame design.  In addition, further analysis of Table 3 shows that in the absence of weighting factors the results using the Laplace Criterion (straight average) or a regret matrix results in the same optimal design.

 

Back Home Up Next