Product Design and Development
6. 1/ FUNCTIONAL DECOMPOSITION AND SYNTHESIS
The overall function may be defined but for complex design
problems no single concept can provide the solution.
Need to decompose problem into smaller parts that are easy to manage.
MSE-415: B. Hawrylo
5
Rev: 02/08/2007
6.1FUNCTIONAL DECOMPOSITION AND SYNTHESIS
Finding the Overall Function: The One-Handed Bar Clamp:
transform the grip force of one hand to a controllable force capable of clamping common objects together
Finding the Overall Function: The X-Ray CT Scanner: the top-level function is “convert electrical energy into an image of the organs of a patient.”
MSE-415: B. Hawrylo
19 Rev: 02/08/2007
6.1 FUNCTIONAL DECOMPOSITION AND SYNTHESIS
Functional decomposition for the one-handed bar clamp
MSE-415: B. Hawrylo
20 Rev: 02/08/2007
6.2 CREATIVE METHODS FOR DESIGN 6.2.1 Generating Design Concepts
Generative design is a design strategy that creates many feasible alternatives to a given product design specification (PDS).
6.2 CREATIVE METHODS FOR DESIGN 6.2.1 Generating Design Concepts
6.2 CREATIVE METHODS FOR DESIGN
The primary purpose of the refinement and evaluation step in concept generation is the identification of creative, feasible, yet still practical ideas. (Convergent thinking dominates this process.)
6.2 CREATIVE METHODS FOR DESIGN 6.2.3 Systematic Methods for Designing
Systematic design methods help the design team consider the broadest possible set of feasible conceptual designs for a given task
6.5 CREATIVE METHODS FOR DESIGN Patents as a Source of Ideas
6.2 CREATIVE METHODS FOR DESIGN
Example: The One-Handed Bar Clamp Step 1: Decompose the Function
6.2 CREATIVE METHODS FOR DESIGN
6.2 CREATIVE METHODS FOR DESIGN
Example: The One-Handed Bar Clamp
6.2 CREATIVE METHODS FOR DESIGN
Example: The One-Handed Bar Clamp
6.5 CREATIVE METHODS FOR DESIGN
Product Design and Development
7.1/ INTRODUCTION
How can a rough conceptual idea evaluated?
Information is often incomplete, uncertain and evolving Evaluation involves: Comparison AND Decision
making
To make a valid comparison concepts must have the same
level of abstraction.
EXAMPLE: Function: To move some object Concepts
To use fluid pressure Linear electric motor.
=> Change “to use fluid pressure” to “hydraulic piston” to levelize the abstraction.
Absolute comparison: Concept is compared to a set of requirements.
Relative comparison: Concepts are compared with each other.
7.2/ Comparison Based on Absolute Criteria
Evaluation based on judgment of feasibility of the design. Categorize concepts into three groups.
1. Not feasible (Ask “Why is it not feasible?” )
2. Conditional - might work (if something else happens)
3. Looks as if it will work
Evaluation based on assessment of technology readiness.
(a) Can the technology be manufactured with known processes? (b) Are the critical parameters that control the function identified?
(c) Are the safe operating latitude and sensitivity of the parameters known? (d) Have the failure modes been identified?
(e) Does hardware exist that demonstrates positive answers to the above four questions?
Evaluation based on go-no-go screening of the customer requirements.
Each customer requirement should be translated into questions that can be addressed by each concept.
Answers: Yes (go)
Maybe (go) (work on weak areas) No (no-go)
7.3/ Pugh Concept Selection Method
Compare each concept to a reference concept.
Determine the criterion to base the comparison.
For each criterion, determine if the concept in question is
better than,
poorer than,
or about the same as the reference concept.
STEP 1: Choose the criteria by which the concepts will be evaluated.
STEP 2: Formulate the decision matrix.
STEP 3: Clarify the design concepts.
STEP 4: Choose the datum concept.
STEP 5: Run the matrix.
STEP 6: Evaluate the ratings.
STEP 7: Establish a new datum and rerun the matrix.
7.3/ Pugh Concept Selection Method
E XAMPLE 7.9
Four concepts for improving the design of an on/off switch in a right-angle drill are: -Concept A is a modest change to the existing switch, and will be the DATUM.
-Concept B adds three buttons for on/off/ and reverse. - Concept C is a track and slider design,
7.3/ Pugh Concept Selection Method
7.3/ Pugh Concept Selection Method
7.4/ Weighted Decision Matrix
Determining weighting factors
Direct Assignment: The team decides how to assign 100 points between the different criteria according to their importance. Dividing each criterion’s score by 100 normalizes the weights. This method is followed by design teams
where there are many years of experience designing the same product line.
Objective Tree: Weighting factors can be determined by using a Hierarchical
objective. Better decisions regarding preferences will be made when the comparisons are made at the same level in the hierarchy.
Analytic Hierarchy Process (AHP): AHP is the least arbitrary and
7.4/ Weighted Decision Matrix
EXAMPLE 7.10
A heavy steel crane hook, for use in supporting ladles filled with
molten steel as they are
transported through the steel mill, is being designed. Two crane
hooks are needed for each steel ladle. These large, heavy
components are usually made to order in the steel mill machine shop when one is damaged and needs to be replaced. Three concepts
(1) built up from flame-cut steel plates, welded together; (2) built up from flame-cut steel
plates, riveted together;
7.5/ Analytic Hierarchy Process (AHP)
A more structured way of constructing a Weighted Decision Matrix.
Well-suited for problems when design objectives have an
hierarchical structure.
Helps with deciding on weights of each criteria.
Uses pair-wise comparison when finding weighting factors for
evaluation criteria.
Uses pair-wise comparison when finding ratings of concepts against
the design criteria.
AHP Process for Determining Criteria Weights
- Complete criteria comparison matrix [C] using 1–9 ratings described in Table 7.6. - Normalize the matrix [C] to give [NormC].
- Average row values. This is the weight vector {W}.
7.5/ Analytic Hierarchy Process (AHP)
As the number of criteria increases, it is difficult to assure consistency.
=> consistency check on [C].
If CR < 0.1 the {W} is considered to be valid; otherwise adjust [C] entries and repeat.
7.5/ Analytic Hierarchy Process (AHP)
Chapter 7-
Concept Evaluation and Selection
(Average row values)
7.5/ Analytic Hierarchy Process (AHP)
Determine Best of Design Alternatives
The process is repeated for each of the five other criteria until all the {P i } of design alternative ratings are complete for each criterion, Table 7.11.