Pahl and Beitz method

A systematic design approach to concept evaluation developed in Germany after World War II.
It is a method of evolution based on use-value analysis.
The overall design of the product is broken down into designs for separate functional modules.
Each modules can then be considered independently with the interactions between them being kept to a minimum.
The major advantage of this approach is the simplification of the subsequent design process for the individual modules.
The major disadvantage of this method is that by reducing the scope for functional sharing, an increase in overall complexity of the product often follows. This can result in manufacturing problems, such as a higher parts count.

The following is a brief overview of the methodology:

1. List the Evaluation Criteria. Essentially, list the factors that the design is being judged upon. The design specifications are one source for the information to create this list. This list should be concise but encompass as many concerns as possible. The criteria should be expressed in way that it is possible to assign numerical values to it from 0 to 1, with 0 being Very Poor and a value near 1 is Excellent.

2. Assign weighting factors to the Evaluation Criteria. The weighting factors are numerical from 0 to 1. They express the relative importance of the criterion to the overall evaluation. Their sum must be equal to 1. Constructing a hierarchical objective tree may be useful during this step. Weights in each level of each objective should sum to 1.

3. Assign Operational Measures to Each Evaluation Criteria. Parameters are assigned to each criterion. These are expressions of what is measured. For example if the subject was light bulbs and the criterion was long life, the operational measure would be life: hours. Parametric values are either measured or estimated for each parameter. In some cases, rough estimates or order of magnitude estimates may be used when it is too early in the design process to have precise numbers.

4. Assign Numerical Evaluation Values to the Individual Criteria. Numerical representations of the "goodness" of a feature is correlated to its description in this step. Typically a 5 or 10 category rating system is used.

Categories	Numerical Values
Unsatisfactory	0
Just Tolerable	1
Adequate	2
Good	3
Very Good or Ideal	4

Categories	Numerical Values
Completely Useless Solution	0
Very Inadequate Solution	1
Weak Solution	2
Tolerable Solution	3
Adequate Solution	4
Satisfactory Solution	5
Good Solution with some drawbacks	6
Good Solution	7
Very Good Solution	8
Solution Better Than Requirements	9
Ideal Solution	10

5. Obtain an Overall Evaluation. With the weights assigned in step 4 and the numerical values from Step 2, an overall evaluation of the concept or design can be obtained by summing the products of the weights and values.

6. Compare and Contrast Alternatives The larger the Overall Weighted Value, the better the proposed alternative is. There are also several supplemental forms of rating.

7. Consider Uncertainties Errors are possible in the above system. examine the final outcomes for consistency.

For additional Information:

Pahl, G., Beitz, W.: Engineering Design: A systematic approach, Springer, 1988

Malmqvist, J., Axelsson, R. and Johansson, M. (1996a) "A Comparative Analysis of the Theory of Inventive Problem-Solving and the Systematic Approach of Pahl and Beitz." In Proceedings of DTM'96, Irvine, CA, USA